Non Muscle-Invasive Bladder Cancer: Intravesical Treatments Beyond Bacille Calmette-Guerin

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1 Non Muscle-Invasive Bladder Cancer: Intravesical Treatments Beyond Bacille Calmette-Guerin Vignesh T. Packiam, MD; Scott C. Johnson, MD; and Gary D. Steinberg, MD An unmet need exists for patients with high-risk non muscle-invasive bladder cancer for whom bacille Calmette-Guerin (BCG) has failed and who seek further bladder-sparing approaches. This shortcoming poses difficult management dilemmas. This review explores previously investigated first-line intravesical therapies and discusses emerging second-line treatments for the heterogeneous group of patients for whom BCG has failed. The myriad of recently published and ongoing trials assessing novel salvage intravesical treatments offer promise to patients who both seek an effective cure and want to avoid radical surgery. However, these trials must carefully be contextualized by specific patient, tumor, and recurrence characteristics. As data continue to accumulate, there will potentially be a role for these agents as second-line or even first-line intravesical therapies. Cancer 2017;123: VC 2016 American Cancer Society. KEYWORDS: bacille Calmette-Guerin (BCG), bladder-sparing, chemotherapy, immunotherapy, intravesical, non muscle-invasive bladder cancer, urothelial neoplasms. INTRODUCTION Urothelial carcinoma of the bladder is prevalent, with 76,960 new diagnoses and 16,390 cancer-specific deaths estimated in the United States alone in Management algorithms are influenced by the metastatic evaluation, staging information from transurethral resection of the bladder tumor (TURBT), and results from repeat TURBT. 2 Durable options for metastatic disease are limited, although there has been recent excitement from immunotherapies. 3 The gold-standard treatment for nonmetastatic muscle-invasive bladder cancer is radical cystectomy. 4 For non muscle-invasive bladder cancer (NMIBC), guidelines by major groups, including the American Urology Association (AUA), the European Association of Urology (EAU), and the National Comprehensive Cancer Network, generally define high-risk disease as carcinoma in situ (CIS) or high-grade Ta or T1 pathology. 4-7 Intravesical bacille Calmette-Guerin (BCG) is commonly used as an adjuvant treatment after repeat TURBT for high-risk NMIBC. 4-7 However, BCG failure occurs in up to 50% of patients, and this increases the risk of cancer progression and even death Radical cystectomy is recommended in this setting, although its significant morbidity poses problems for elderly patients unfit for this major procedure or those who desire bladder-sparing options. 11 There are no clear guidelines or standard second-line intravesical therapies in this setting. 12 In fact, even though valrubicin is a Food and Drug Administration (FDA) approved agent for BCG failures, it has been shown to have a durable 2-year efficacy rate of only 8%. 13,14 The longstanding need for second-line intravesical therapies in the setting of BCG failure has led to a recent surge of potential salvage treatments. 15 This article reviews the use and effectiveness of BCG, examines the array of alternative potential intravesical agents, and highlights challenges in developing additional therapies for NMIBC. HISTORY AND EMERGENCE OF INTRAVESICAL BCG In 1908, Albert Calmette and Camille Guerin sought to use an attenuated strain of Mycobacterium bovis as a vaccine for tuberculosis. After creating 230 subcultures, they found a stable, nonvirulent strain that became known as BCG. 16 Because of an inability to preserve viable bacteria, BCG had undergone 1173 serial passages by Daughter strains were extracted at irregular times and were subsequently named after their manufacturer and site of origin (eg, Tice, Connaught, Moscow, and Tokyo). 17 A potential relation between cancer and tuberculosis was described in an autopsy study in 1929; Corresponding author: Vignesh T. Packiam, MD, Section of Urology, Department of Surgery, University of Chicago Medical Center, 5841 South Maryland Avenue, MC-6038, Chicago, IL 60637; Fax: (773) ; vignesh.packiam@uchospitals.edu Section of Urology, Department of Surgery, University of Chicago Medical Center, Chicago, Illinois. DOI: /cncr.30392, Received: April 26, 2016; Revised: August 10, 2016; Accepted: August 11, 2016, Published online November 2, 2016 in Wiley Online Library (wileyonlinelibrary.com) 390 Cancer February 1, 2017

2 NMIBC: Beyond BCG/Packiam et al Pearl 18 reported lower rates of malignancy in patients with tuberculosis. Although encouraging reports of BCG for various cancers created enormous interest in its use, BCG was ultimately abandoned in favor of more effective therapies for all but bladder cancer. 19 The bladder s unique characteristics make it an ideal organ for local therapy. Access to the bladder can be obtained via the urethra, and the bladder urothelium provides a barrier that limits systemic absorption. Bateman 20 first recognized the potential for intravesical therapy in 1955 and described intravesical thiotepa administration in 1 patient. In 1976, Morales et al 21 reported the first use of intravesical BCG in 10 patients treated with intravesical and intradermal BCG. There were no short-term recurrences in 7 patients appropriate for analysis. 21 This promising report spurred multiple subsequent trials, including a randomized study in 1980 by Lamm et al 22 comparing endoscopic management alone with endoscopic management plus BCG. Recurrences dropped from 42% to 22% with the addition of BCG. In 1990, BCG joined thiotepa as an FDA-approved intravesical agent for NMIBC. OVERVIEW OF BCG The mechanism by which BCG induces antitumor responses is not fully understood, although there has been longstanding recognition that its effects are mediated through immune activation. Successful BCG therapy relies on an intact immune system and direct contact with live BCG. 23 After BCG instillation, fibronectin facilitates urothelial attachment. 24 BCG is then internalized by urothelial and dendritic cells, which release a number of cytokines, including interleukin 6 (IL-6) and granulocytemacrophage colony-stimulating factor (GM-CSF). 25 As a result, granulocytes, macrophages, and lymphocytes are recruited. Ultimately, cell death results from direct cytotoxicity and the release of apoptotic factors, including tumor necrosis factor related apoptosis-inducing ligand (TRAIL). Intravesical BCG is administered via a urethral catheter, and patients are encouraged to retain the medication for 2 hours. Although the optimal schedule for BCG delivery remains unknown, an induction course of 6 weekly treatments, as first described by Morales et al, 21 remains the de facto standard. This schedule was partially created for convenience; Frappier BCG was originally packaged into 6 vials. In addition, Morales et al observed that side effects from BCG generally lasted less than a week. Furthermore, more than 3 weeks of treatment was necessary for some patients to develop a delayed hypersensitivity reaction, and a response by weeks 4 to 5 was not further enhanced by additional BCG. 21 Further studies confirmed that 6 weekly treatments may be most appropriate for induction. 26 Multiple trials have demonstrated that BCG should be continued beyond induction to be most effective. 8,27,28 Both AUA and EAU guidelines advocate maintenance BCG, although they do not specify the exact duration or schedule. The most commonly used dosing schedule is the 3-year regimen reported by the landmark Southwest Oncology Group (SWOG) trial in 2000: 3 weekly instillations at 3 months, 6 months, and every 6 months thereafter for 3 years after the initial induction. 29 Although recurrence-free survival and progression-free survival were improved, only 16% of patients tolerated the entire 3-year maintenance course. However, in a subsequent large randomized controlled trial of 1355 patients, the European Organization for Research and Treatment of Cancer showed that up to 35% of patients completed one-third and full-dose 3-year maintenance regimens, whereas up to 62% of patients completed 1-year maintenance regimens. 30 A more recent analysis of this trial found that only 20.3% of patients discontinued BCG because of local or systemic side effects, whereas many stopped for other reasons, including inefficacy, administrative errors, loss to follow-up, the development of additional comorbidities, and death. 31 Multiple meta-analyses support the superiority of adjuvant BCG for preventing recurrences over TURBT alone or TURBT plus intravesical chemotherapy alone. 27,28,32-34 Malmstrom et al 27 used individual data from 2820 patients and found that BCG with maintenance resulted in a 32% reduction of recurrences in comparison with mitomycin C (MMC). Similarly, reviewing 11 studies, Bohle et al 34 showed that BCG was more effective in reducing recurrences than MMC (odds ratio, 0.56), with longer than 1-year maintenance therapies showing further improvements (odds ratio, 0.43). BCG also delays or prevents tumor progression. In a landmark meta-analysis of 24 trials, the European Organization for Research and Treatment of Cancer showed a 27% reduction in progression to invasive disease. 8 Another metaanalysis showed a 23% reduction in progression for patients treated with BCG and maintenance in comparison with MMC. 34 Although many accept that BCG alters progression, a lack of a significant benefit in several studies has fueled controversy. 4,27,28 These conflicting results may be secondary to the heterogeneity of disease in patients between studies. 5 Side effects of BCG are not infrequent; most patients transiently experience flu-like or irritative voiding Cancer February 1,

3 symptoms during treatment. No treatment is generally required beyond symptomatic management with painkillers and antispasmodics. Severe systemic side effects are rare and include hepatitis, pneumonitis, and disseminated BCG infections. Given the prevalence of local side effects in early studies, some providers previously regarded BCG as intolerable and cited treatment discontinuation rates ranging from 20% to 80%. 35 Many efforts have been made to reduce BCG side effects and improve tolerability. One commonly used strategy is dose reduction. Early reports suggested that reduced-dose BCG may be equally effective but less toxic in comparison with full-dose BCG. 36,37 In 2002, Martinez-Pineiro et al 38 published a randomized trial of 500 patients showing that half-dose BCG reduced toxicity without sacrificing overall efficacy. However, their results also suggested that high-risk patients may benefit from full-dose regimens. Doses lower than one-third have been shown to yield poor outcomes. 30 Recent data show that BCG is currently better tolerated. A 2013 study surveyed 102 urologists who used BCG to treat 409 non clinical trial patients with intermediate- to high-risk NMIBC; it found that 90% of the patients tolerated a 1-year or longer course of BCG. 39 BCG FAILURE Although many patients presenting with NMIBC are successfully treated, up to 80% will suffer recurrence, and as many as 45% may progress to muscle-invasive disease within 5 years. 40 There is a general consensus among expert groups that BCG failure refers to NMIBC that recurs or progresses within 6 months of BCG therapy. 12 O Donnell and Boehle 41 defined now commonly used subclassifications for BCG failure: BCG-refractory (failure to achieve a disease-free status within the first 6 months after induction BCG with maintenance or retreatment), BCGresistant (recurrent or persistent lower stage/grade tumor at 3 months with a complete response at 6 months), BCGrelapsing (recurrence of disease after a disease-free status was achieved within 6 months), and BCG-intolerant (disease recurrence after an inadequate treatment course was applied because of serious adverse effects or symptomatic intolerance). Most recently, experts have recommended the term BCG-unresponsive. 42 A consensus publication from the International Bladder Cancer Group sought to define a more standardized high-risk population for clinical trial design. 43 The goal was to allow single-arm trials for patients who desired/required further intravesical therapy because of their eligibility for radical cystectomy but not for additional BCG. The authors deemed that this should not include BCG-resistant or BCG-intolerant patients because BCG does not truly fail for these patients and they can, therefore, be considered candidates for additional BCG. This has the effect of 1) standardizing future inclusion criteria and trial homogeneity to allow cross-trial comparisons (this is currently very limited) and 2) improving statistical power and allowing more effective accrual because of a lack of a need for control arms. The first definition of BCG-unresponsive from this consensus publication by Kamat et al 43 essentially [included] BCG refractory and BCG relapsing (within 6 months of last BCG exposure) ; this referred to patients with 1) persistent high-grade disease at 6 months despite adequate BCG (at least 5 of 6 induction instillations and at least 1 maintenance dose [2 of 3 instillations] in a 6-month period), 2) any stage or grade of progression within the first 3 months after the first BCG cycle, and 3) recurrence of high-grade disease after the achievement of a disease-free state at 6 months after adequate BCG (patients should be within 6 months of the last BCG exposure). A publication by O Donnell s group 44 additionally qualified that BCGunresponsive patients should also include patients with persistent or recurrent CIS within 12 months for whom 2 courses of BCG (or adequate BCG) have failed. Table 1 highlights the heterogeneity of inclusion criteria across salvage intravesical therapy trials. Almost no trials had high percentages of truly BCG-unresponsive patients, largely because of the failure of either an unknown number or a single course of prior BCG. The difficulty in comparing outcomes for dissimilar groups promotes the use of standardized definitions for BCG failure or unresponsiveness. Predicting those at the highest risk of BCG treatment failure is of particular interest, especially because delaying definitive radical surgery may worsen survival. 69,70 Clinical factors can be used to determine risk; one scoring system found tumor size, multiplicity, and prior recurrence to be the most important factors predicting recurrence, whereas the tumor grade, stage, and presence of CIS were most predictive of progression. 71 Other studies have recently investigated predicting BCG responsiveness by changes in serum tumor markers (IL-2) or combinations of multiple urinary cytokines (IL-2, IL-6, IL-8, IL- 18, IL-1ra, TRAIL, interferon-c [IFN-c], IL-12(p70), and tumor necrosis factor a). 72,73 Recently updated 2016 EAU guidelines still recommend radical cystectomy for patients for whom BCG has failed (persistent high-grade T1 tumor at 3 months, persistent CIS at 3 and 6 months, high-grade tumor during BCG therapy, or progression to muscle-invasive disease). 74 These guidelines further state that level 3 evidence 392 Cancer February 1, 2017

4 NMIBC: Beyond BCG/Packiam et al TABLE 1. Summary of Series Reporting on Intravesical Therapies for High-Risk Non Muscle-Invasive Bladder Cancer Source Treatment Agent (Control Agent) Trial Design a No. of Patients in Treatment Arm (Control Arm) Patients at High Risk Patients With Prior BCG Exposure BCG- Unresponsive Patients b BCG- Intolerant or Relapsing Patients Primary Follow-Up Duration/ Complete Response c Success Rate/ Primary Follow-Up Duration c Complete Response at 1 y c Steinberg / Valrubicin (NA) Single arm 90 (NA) 100% 100% 70% No 6 mo 18% 10% Dinney Nepple BCG 1 IFN (BCG) RCT 346 (324) Unknown 0% 0% No 2 y 58% 70% Puri Apaziquone (NA) Single arm 12 (NA) 0% 33% 0% Unknown 2 wk 75% NA van der Heijden Apaziquone (NA) Single arm 46 (NA) 0% 22% 0% No 2 wk 67% NA Hendricksen Apaziquone (NA) Single arm 53 (NA) 44% 40% Unknown Unknown 1 y 65% 65% Alfred Witjes MMC Synergo Single arm % 67% 33% 4% 2 y 50% NA Glashan IFN (low dose) RCT 47 (38) 100% 0% 0% 0% 3 mo 43% 22% Hudson IFN Single arm 12 50% 100% 33% 16% 3 mo 34% 8% Joudi IFN Single arm % 46% 16% 8% 2 y 45% d NA Morales MCWE (low dose) RCT 25 (30) 100% 82% 38% Unknown 26 wk 46% NA Morales MCNA Single arm % 100% 58%-75% 22% 1 y 22% e 25% Gomella Vaccinia Single arm 4 100% Unknown Unknown Unknown NA NA NA Burke CG0070 Single arm 35 49%-100% 100% Unknown Unknown 10 mo 49% NA Dinney Adenovirusmediated Single arm 17 88% 100% 88% Unknown 3 mo 43% 35% IFN Uchibayashi PDT 5-ALA Single arm % Unknown Unknown Unknown 3 mo 73% 48% Berger PDT 5-ALA Retrospective 31 >23% 32% 3%-32% Unknown 8 mo 52% NA Bader PDT 6-ALA (high dose) Kowalski Oportuzumab monatox (12 wk) Dual arm 13 (4) 88% 71% 0%-71% Unknown 53% 6 mo NA Dual arm 23 (22) 100% 100% 0%-71% 13% 40% 3 mo 16% Kaasinen MMC/BCG (BCG) RCT % Unknown Unknown Unknown 75% 3 mo 79% Skinner Gemcitabine Single arm 47 89% 100% 19% 13% 47% 3 mo 28% Breyer Gemcitabine/MMC Retrospective 10 90% 90% 60%-70% 10% 60% 3 mo 60% Cockerill Gemcitabine/MMC Retrospective 27 85% 89% 0%-63% Unknown 37% 15 mo NA Valaer Gemcitabine/ Retrospective 45 91% 91% 42% 40% 66% 3 mo 54% docetaxel Bassi Paclitaxel-HLA Single arm % 100% 100% 0% 60% 7 wk NA McKiernan (Nab-)paclitaxel Single arm % 100% NA 4% 36% 3 mo 36% Abbreviations: ALA, aminolevulinic acid; BCG, bacille Calmette-Guerin; HLA, human leukocyte antigen; IFN, interferon; MCNA, mycobacterial cell wall nucleic acid complex; MMC, mitomycin C; MCWE, mycobacterial cell wall extract; NA, Not available in publication; PDT, photodynamic therapy; RCT, randomized controlled trial. a Trials were prospective unless otherwise stated. b These patients were BCG-unresponsive according to Kamat et al s definition 43 except for the inclusion of patients with persistent/recurrent carcinoma in situ at 12 months for whom 2 courses of BCG had failed. 45 c Outcomes are provided for the entire cohort in the main treatment arm unless otherwise stated. d For BCG-failure patients only. e For BCG-refractory patients only Cancer February 1,

5 exists for bladder-preservation therapies for these patients. The updated AUA guidelines from 2016 also state that in a high-risk patient with persistent or recurrent disease within one year following treatment with two induction cycles of BCG or BCG maintenance, a clinician should offer radical cystectomy. 75 For those unwilling or unfit for cystectomy in this group, a clinician may recommend clinical trial enrollment or offer this patient intravesical chemotherapy when clinical trials are unavailable. RATIONALE FOR OTHER AGENTS? Novel intravesical agents have potential roles as both firstand second-line therapies for NMIBC. Effective secondline agents for BCG failures are the primary focus of contemporary trials. Alternative first-line agents have been considered because of concerns about BCG and recent shortages. BCG therapy fails up to 50% of patients in some series. 76 A Surveillance, Epidemiology, and End Results Medicare study assessed more than 23,000 patients from 1991 to 2003 and revealed that a mere 27% of patients with high-grade NMIBC received adjuvant BCG. 77 Finally, worldwide BCG shortages beginning in 2012 have sparked the utilization of alternative first-line treatments. 78 PREVIOUSLY INVESTIGATED ALTERNATIVE FIRST-LINE INTRAVESICAL THERAPIES No alternative first-line treatments have been shown to be as effective as BCG. 79 Thiotepa, adriamycin, and MMC were common before the widespread adoption of BCG. MMC persists as an alternative first-line treatment for BCG-naive patients primarily during BCG shortages. 79 Meta-analyses have shown mixed results for comparisons of MMC and BCG, although many believe that MMC is associated with a heightened risk of recurrence in comparison with traditional BCG regimens. 28,29,34,80 A randomized trial showed that IFN and BCG combination therapy in BCG-naive patients did not improve efficacy while increasing fever and constitutional symptoms. 45 Apaziquone (EO9) is an alkylating agent like MMC that has been used in the salvage intravesical setting. 46 It is converted to a cytotoxic agent after it undergoes enzymatic activation. The first phase 2 study for this treatment assessed 46 patients with no prior intravesical therapy, and 2-year follow-up showed 39% recurrence-free survival. 57,81 Another phase 2 study of 53 patients found 55% recurrencefree survival at 18 months. 48 Changing drug delivery to improve intravesical absorption has also been used in the first-line setting. First, simple techniques, including increasing the total drug dose, decreasing the volume of the diluent, and alkalinizing urine, have been shown to improve efficacy in a randomized phase 3 trial for MMC. 82 Thermochemotherapy is a concept that promotes the transvesical absorption of intravesical agents with hyperthermia. A 2003 study of 83 patients compared standard intravesical MMC and local microwave hyperthermia regimens. 83 Hyperthermia was applied through the Synergo device, a 915-MHz intravesical microwave applicator inserted through a special 20F catheter. The complete response rates were 83% and 43% in the hyperthermic and standard MMC arms, respectively. However, a more recent 2009 study across 15 European centers using the MMC Synergo system assessed 51 patients with only CIS; BCG had previously failed for 34 of these patients (17 were BCG-refractory, 2 were BCGintolerant, and 15 were BCG-relapsing). 49 In this highrisk cohort, the study demonstrated an initial complete response rate of 92% and a 2-year complete response rate of 50%. Another protocol for MMC instillation used electromotive transport, which involved pulsed energy to generate electro-osmotic currents. 84 However, comparisons of electromotive MMC and BCG in the BCG-naive setting have been equivocal. 84 A systematic review and meta-analysis evaluated the addition of intravesical chemotherapies to BCG but found these to be less effective than traditional BCG. 85 The most frequent alternatives to the SWOG adjuvant BCG regimen are probably reduced-dose protocols, especially one-third dose BCG. 29,30 At this time, because of its proven superiority to all other potential treatments, BCG remains the gold-standard first-line treatment. SALVAGE INTRAVESICAL THERAPIES Alternative salvage intravesical therapies after BCG failure fall into 2 broad categories: immunotherapy and chemotherapy (Fig. 1). Immunomodulators aim to augment BCG s successful activation of the immune response. Chemotherapies cause direct cytotoxic damage and shut down deregulated tumor replication pathways. Both of these classes have benefited from novel intravesical delivery systems that boost drug absorption in comparison with traditional intravesical drug instillation techniques. We review these innovations to illustrate the current landscape of future treatment options. Previously Investigated Salvage Intravesical Immunotherapies IFN is a pleiotropic immune modulator that has been studied for decades because of its immunologic antitumor and antiproliferative effects. This cytokine was first assessed in a randomized trial of 85 patients in 1990 that 394 Cancer February 1, 2017

6 NMIBC: Beyond BCG/Packiam et al Figure 1. Classes of salvage intravesical therapies. BCG indicates bacille Calmette-Guerin; PD-1, programmed death 1. a Only investigated in the first-line intravesical setting. b Only investigated in the metastatic setting. c Investigated in intravesical bladder cancer animal models. demonstrated only a 22% complete response rate in the high-dose arm after 1 year. 50 Another smaller trial in 1995 demonstrated that only 1 of 12 patients (8%) had a complete response after 2 years. 51 Because of the poor success of monotherapy, efforts were made to combine IFN with BCG in the salvage setting. However, a randomized trial by Joudi et al 52,86 assessing BCG with IFN showed that the 2-year cancer-free survival rate for the BCGrefractory patients was only 13%. Response rates were also significantly poorer for patients with short-term recurrence. 86 Another alternative therapy actually stemmed from a precursor to BCG. In 1996, Chin et al 87 demonstrated the efficacy of emulsified Mycobacterium phlei cell walls in treating bladder cancer in a murine model. A new formulation of this complex called mycobacterial cell wall nucleic acid complex (MCNA) was engineered in 1997; it is composed of both complex cell wall and DNA and theoretically facilitates both immunomodulatory and direct cytotoxic tumor-killing mechanisms. 88 Two trials subsequently evaluated the efficacy of MCNA. 53,54 The first trial was limited by a short follow-up period and the inclusion of both BCG-naive and BCG-unresponsive patients; it demonstrated a 46% 2-year complete response rate in the high-dose arm with a 33% serious adverse event rate. 53 The more recent phase 3 trial in 2015 by Morales et al 54 included 129 patients for whom BCG had failed. MCNA was given only at the higher 8-mg dose with instillations every 6 months for 2 years (after instillation and 3-month maintenance therapy). Patients with relapsing BCG had improved 1-year disease-free survival in comparison with BCG-refractory patients (39% vs 22%, respectively). Longer follow-up (median, 34 months) revealed that the 2-year complete response rate was 19%. Interestingly, those who responded at 1 year had a durable response for more than 2 more years, whereas almost onethird of the patients who had undergone cystectomy for progression were found to have T2 disease. MCNA (Urocidin) failed to gain FDA approval in Emerging Salvage Immunotherapies Oncolytic viruses are appealing choices for tumorselective cytotoxic gene delivery. In 2001, Gomella et al 55 first published a proof-of-concept study using the vaccinia virus, an active constituent of the vaccine used to cure smallpox by the World Health Organization. This trial assessed toxicity with a pathologic bladder examination after intravesical viral instillation in 4 patients with muscleinvasive bladder cancer destined for cystectomy. After 3 instillations, cystectomy revealed the recruitment of Cancer February 1,

7 lymphocytes and urothelial inflammation. Furthermore, 3 of 4 patients were alive at 4 years, and this confirmed the long-term safety after transfection with recombinant viruses. In 2012, a phase 1 study examined CG0070, a tumor-selective adenovirus designed to preferentially replicate in and destroy retinoblastoma pathway defective cells through transgene expression of GM-CSF. 56 GM- CSF is essential for immunogenic responses through antigen-presenting cell activation. Evaluating 35 patients, this study confirmed the safety and efficacy of this selectively oncolytic virus. Urine and plasma GM-CSF concentrations peaked between 2 and 8 days and then fell to normal levels; this signified the temporary nature of the immunologic response. Furthermore, a higher clinical response was noted in 12 retinoblastoma pathway defective patients (58.3%) in comparison with wild-type patients (20%), and this suggested specificity of replication. Phase 2 and 3 trials are currently ongoing. Recombinant adenoviral interferon a2b is another tumor-selective virus administered via an intravesical route. 57 A phase 1 trial assessing 17 patients demonstrated a prolonged elevation of urine IFN levels with only transiently low serum IFN levels. 57 Among patients with significant urinary IFN levels, 43% experienced a complete response at 3 months. However, longer term data and larger series are needed for this agent. Photodynamic therapy has shown mixed results over time. This treatment involves selective tumoral uptake of a photosensitizing agent followed by cytotoxic irradiation by a unique wavelength of light. 90 The first agent used was 5-aminolevulinic acid, a precursor of protoporphyrin that is preferentially taken up by tumors. Intravenous 5- aminolevulinic acid was evaluated in the 1990s for patients with recurrent CIS. 58,91 There was a moderate 1- year complete response rate (31%). Significantly, 19% of patients experienced bladder contractures, which were previously reported in smaller series using this agent. 92 Intravesical 5-aminolevulinic acid was later evaluated in 10 patients and conferred a 40% 1-year complete response rate. 59 Hexaminolevulinic acid is a similar precursor that yielded only a 12% complete response rate at 20 months. 60 These low response rates have precluded the widespread adoption of photodynamic therapies. Intravesical oportuzumab monatox (VB4-845) and intradermal HS-410 are 2 unique immunomodulatory compounds. VB4-845 is a recombinant fusion protein with a humanized anti epithelial cell adhesion molecule antibody linked to Pseudomonas exotoxin; it is selectively internalized by tumor cells and leads to apoptosis. 61 In 2012, a phase 2 study examined 46 patients treated with this interesting agent, but it showed that despite excellent tolerability, there was only a 16% 1-year complete response rate. HS-410 is an engineered tumor cell line that produces gp96, a heat shock protein capable of activating a cytotoxic CD8 1 response. These engineered tumor cells also produce tumor antigens, which, when combined with gp96 as an extracellular delivery system, result in selective activation of antitumoral CD8 1 T cells. Notably, although the cell line was initially reported to be a bladder cancer cell line, it was later identified as a prostate cancer cell line. Preliminary phase 2 trial results were recently reported; they showed more robust tumor-infiltrating cell induction and tumor-infiltrating cell clonality in diseasefree patients. 93 The relative success of immune checkpoint inhibition for various metastatic cancers has sparked interest in using these novel treatments for the NMIBC population. 3,94 Although immune checkpoints normally allow self-tolerance, tumor cells exploit this regulatory pathway by overexpressing inhibitory immune checkpoint molecules. Therefore, recent therapies have used monoclonal antibodies to block immune checkpoint receptors (cytotoxic T lymphocyte antigen and programmed death 1) or immune checkpoint ligands (B7 and programmed death ligand 1 [PD-L1]). Numerous studies have demonstrated impressive clinical responses to these agents in the setting of metastatic bladder cancer, which traditionally is associated with very poor survival. 95 A recent study evaluated systemic avelumab, an anti PD-L1 agent, for NMIBC in a mouse model. 96 The investigators found that mice treated with avelumab experienced greater regression of tumors than those treated with isotype control antibodies. Furthermore, immunohistochemical staining confirmed complete tumor regression in 8 of 10 mice that underwent checkpoint inhibition. These results have raised enthusiasm for the utilization of these treatments for patients with BCG-naive NMIBC or BCG failures. In fact, there are currently ongoing trials evaluating concurrent PD-L1 inhibitor treatment with induction BCG. Salvage Chemotherapies and Novel Delivery Platforms The use of intravesical chemotherapy in the setting of BCG failure has shown mixed results, and its role remains unclear. 15 Older classes of agents include alkylating agents (MMC and thiotepa), anthracyclines (doxorubicin, epirubicin, and valrubicin), antimetabolites (gemcitabine), and taxanes (paclitaxel and docetaxel). 15,90 Newer agents, combination therapies, and novel intravesical drug delivery systems have resulted in recently improved results. 396 Cancer February 1, 2017

8 NMIBC: Beyond BCG/Packiam et al MMC and thiotepa are both alkylating agents that have been studied for decades. These treatments are largely historical in the setting of BCG failure. Thiotepa was shown to eradicate residual papillary tumors in 1976 and remains one of the few FDA-approved intravesical agents. 97 However, its use has largely been limited by its small molecular weight, which facilitates increased systemic absorption and subsequent myelosuppression. MMC has been shown to be more effective than thiotepa, but a large series of 304 BCG-naive patients showed that traditional BCG is superior to mixed maintenance regimens with MMC; this suggests against its efficacy as a salvage agent. 62,98 The anthracyclines are another older class of intravesical chemotherapies. Valrubicin is the most notable because it is the sole FDA-approved therapy for patients with BCG-refractory CIS who refuse cystectomy. 13 However, its approval in 2000 was likely based on the low success rates seen in an earlier era of treatments; valrubicin yielded only an 8% complete response rate at 2 years, which is lower than the rate for most modern therapies. 13,14 Epirubicin and doxorubicin are older anthracyclines that yield poorer success and notably increased irritative bladder symptoms. 99 A 2012 Cochrane review of intravesical gemcitabine assessed 704 patients from 6 randomized trials, and it ultimately found overall comparisons with BCG to be equivocal. 100 Skinner et al 63 recently published results from SWOG S0353, a phase 2 trial assessing 47 patients for whom 2 prior BCG courses had failed and who subsequently received intravesical gemcitabine. This study demonstrated a reasonable 21% 2-year complete response rate. Other studies have assessed salvage combination treatment with gemcitabine and other agents. One small series of 10 patients with BCG-refractory disease followed a course of intravesical gemcitabine with MMC treatment, and it found a 60% complete response rate at 14 months. 64 Another series of 27 patients (including 24 BCG failures) evaluated combination treatment with concurrent gemcitabine and MMC, and it showed a 37% disease-free survival rate at a median of 22 months. 65 Although these combination therapies are promising, larger series with longer follow-up are needed. Docetaxel has a minimal role as an intravesical agent, although some BCG failure protocols have shown moderate success when sequentially using this agent with gemcitabine. 66 Intravesical paclitaxel is limited by high lipophilicity and penetration of the urothelium, which can result in systemic toxicity. Novel delivery platforms have conjugated paclitaxel to overcome these issues; this has increased tumor cell selectivity. Bassi et al 67 reported a phase 1 study of conjugated paclitaxel hyaluronic acid in 16 patients and demonstrated a 60% complete response rate, although this was assessed only 1 week after the last instillation. The hydrophilic tendency of hyaluronic acid limited overall toxicity, and no serious adverse events were attributable to the treatment. Hyaluronic acid also facilitated specific binding to CD44v, a cell surface marker isoform that is overexpressed in urothelial carcinoma. Nanoparticle albumin bound (nab-)paclitaxel is another formulation that has been developed to decrease systemic toxicity and improve tumor specificity. 68 Phase 2 trial results for 28 patients for whom BCG had failed demonstrated a 36% 1-year complete response rate. OBSTACLES IN CLINICAL TRIALS FOR NMIBC The evaluation and subsequent approval of novel treatments for NMIBC are limited by several factors, including disease heterogeneity, a lack of a control and/or gold standard, difficult patient accrual, and varying endpoints. 43 The International Bladder Cancer Group recently published formal recommendations to address these issues and promote uniform reporting for future studies. 43 Specifically considering high-risk BCG-naive disease, the group recommended superiority trial designs for comparison with the current standard, BCG. Because of the high risk of progression and mortality with no treatment, placebo-controlled trials are unethical. These wellintentioned recommendations pose difficulties for evaluating new agents for these patients because accrual is often significantly and prohibitively slower in dual-arm studies. Thus, for BCG to be supplanted, novel intravesical treatments will likely have to show improved efficacy in patients for whom BCG has failed. Paradoxically, these patients have more resistant tumors that are more difficult to treat. Trials assessing BCG failures are often confounded by highly heterogeneous types, including BCG-refractory, BCG-relapsing, BCG-intolerant, and BCG-unresponsive patients. A mixture of these patients in trials can cause difficulty in interpreting the results, especially because some failure types such as BCG-relapsing patients have been shown to have superior outcomes in comparison with others (Table 1). 101 Radical cystectomy is the gold standard for these patients. The lack of standard bladdersparing second-line treatments ethically allows single-arm trials, placebo arms, or investigator-choice comparators for patients who are unfit for or refuse cystectomy. 43 Kamat et al 43 also identified the 1-year complete response to be an appropriate endpoint for these studies with a Cancer February 1,

9 clinically meaningful and realistic recurrence-free rate of at least 30% during this timeframe. In conclusion, intravesical BCG has now been used for 4 decades and is one of the few FDA-approved intravesical treatments for NMIBC. However, there is a heterogeneous and large field of patients who are not adequately treated by this medication. BCG will likely remain the gold-standard first-line intravesical treatment for high-risk NMIBC until another agent shows dramatic efficacy in the salvage setting. A variety of novel agents for BCG failures have arisen, and they often harness innate cancer-killing mechanisms. Promising results from these agents are encouraging and increase the anticipation of ongoing trials for immunomodulation. However, hurdles must still be overcome in the context of complicated clinical trials for this patient population. FUNDING SUPPORT No specific funding was disclosed. CONFLICT OF INTEREST DISCLOSURES Gary D. Steinberg is a consultant for Cold Genesys, Heat Biologics, Telesta, Taris Biomedical, Photocure, Roche/Genentech, UroGen, and Fidia. AUTHOR CONTRIBUTIONS Vignesh T. Packiam: Study design, conceptualization, methodology, data analysis and interpretation, drafting of the manuscript, revisions, final article approval, and accountability for all aspects of the work. Scott C. Johnson: Study design, conceptualization, methodology, data analysis and interpretation, drafting of the manuscript, revisions, final article approval, and accountability for all aspects of the work. Gary D. Steinberg: Study design, conceptualization, methodology, data analysis and interpretation, drafting of the manuscript, revisions, final article approval, accountability for all aspects of the work, supervision, and content guarantor. REFERENCES 1. Siegel RL, Miller KD, Jemal A. Cancer statistics, 2016: cancer statistics, CA Cancer J Clin. 2016;66: Richards KA, Smith ND, Steinberg GD. 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