Heterogeneity of Triple-Negative Breast Cancer: Histologic Subtyping to Inform the Outcome

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1 Heterogeneity of Triple-Negative Breast Cancer: Histologic Subtyping to Inform the Outcome Emilia Montagna, 1 Patrick Maisonneuve, 2 Nicole Rotmensz, 2 Giuseppe Cancello, 1 Monica Iorfida, 1 Alessandra Balduzzi, 1 Viviana Galimberti, 3 Paolo Veronesi, 3,4 Alberto Luini, 3 Giancarlo Pruneri, 4,5 Luca Bottiglieri, 5 Mauro G. Mastropasqua, 5 Aron Goldhirsch, 6 Giuseppe Viale, 4,5 Marco Colleoni 1 Abstract Original Study Emerging data clearly indicate that triple-negative breast cancer (TNBC) is a heterogeneous class with variable prognosis according to clinical, pathologic, and genetic factors. The aims of this study were to determine the outcome of special types of TNBC. We included 781 patients with immunohistochemically defined TNBC. The analysis of the results suggests that distinct prognostic implications may derive from the specific histotype of TNBC. Background: This study assesses outcome in terms of disease-free survival (DFS) and overall survival (OS) of special types of triple-negative breast cancer (TNBC). Patients and Methods: We identified 8801 women with first primary nonmetastatic breast cancer operated on at the European Institute of Oncology between 1997 and Of these patients, 781 consecutive patients with immunohistochemically defined TNBC were selected for the analyses. We explored patterns of recurrence by histologic type. Median follow-up was 5.7 years (range 0-13 years). Results: The 5-year DFS was 77% for TNBC, 68% for human epidermal growth factor receptor 2 (HER2)-positive breast cancer, and 84% and 95% for luminal B and luminal A breast cancer, respectively. From 781 TNBC subtypes, 693 cases (89%) were classified as ductal not otherwise specified (NOS) (invasive ductal carcinoma [IDC]), 29 were classified as apocrine (3.7%), 18 (2.3%) were classified as lobular, 10 (1.2%) were classified as adenoid cystic, and 10 (1.2%) were classified as metaplastic. Five-year DFS and OS were 77% and 84% for patients with ductal carcinoma, 56% and 89% for patients with metaplastic carcinoma, and both 5-year DFS and OS were 100% for patients with adenoid cystic and medullary carcinomas, respectively. Conclusion: Distinct prognostic implications may derive from the specific histotype of TNBC. The identification of these special types has a significant clinical utility and should be considered in therapeutic algorithms. Clinical Breast Cancer, Vol. 13, No. 1, Elsevier Inc. All rights reserved. Keywords: Adjuvant therapy, Breast cancer, Histologic subtype, Special types, Triple negative 1 Research Unit in Medical Senology, Department of Medicine, European Institute of Oncology, Milan, Italy 2 Division of Epidemiology and Biostatistics, European Institute of Oncology, Milan, Italy 3 Division of Senology, European Institute of Oncology, Milan, Italy 4 University of Milan School of Medicine, Milan, Italy 5 Division of Pathology, European Institute of Oncology, Milan, Italy 6 Department of Medicine, European Institute of Oncology, Milan, Italy Submitted: Mar 27, 2012; Revised: Sep 13, 2012; Accepted: Sep 13, 2012; Epub: Oct 24, 2012 Address for correspondence: Emilia Montagna, MD, Research Unit in Medical Senology, Department of Medicine, European Institute of Oncology, Milan Italy Fax: ; contact: emilia.montagna@ieo.it Introduction Four major molecular classes of breast cancer (luminal A and B, basal-like, and human epidermal growth factor receptor 2 [HER2] overexpressing) are identified by comprehensive gene expression profile analyses. 1 The basal-like subgroup is characterized by expression of basal cell (myoepithelial) cytokeratins 5/6 and 17 and they make up approximately 15% of all types of breast cancer. 2,3 Triple-negative breast cancer (TNBC) describes a subset of breast cancer that does not express estrogen receptor (ER), progesterone receptor (PR), and HER2 receptor. The features of the TNBC subgroup roughly parallel those of the basal-like subgroup. However, although most basal-like cancers do not express ER, PR, or HER2, a small number do and therefore the overlap between basal-like breast cancer and TNBC is not complete. 4,5 Moreover, in the study of Perou et al, only invasive ductal carcinomas (IDCs) were analyzed, leaving uncertain the role of other histologic subtypes of breast cancer. 1 Emerging data clearly indicate that TNBC is a heterogeneous class with variable prognosis according to clinical, pathologic, and genetic /$ - see frontmatter 2013 Elsevier Inc. All rights reserved. Clinical Breast Cancer February

2 Special Types of Triple-Negative Breast Cancer Table 1 Patients and Tumor Characteristics by Molecular Subtype All Breast Cancers Triple Negative (%) P Value All (8.9) Age (y) (21.2) (8.4) (8.2) (8.8) Menopausal Status Premenopausal (9.0) Postmenopausal (8.9) Perimenopausal (7.1) Histologic Subtype Ductal (10.0) Lobular (2.1) Mucinous (0.7) Cribriform (0.4) Medullary 8 4 (50.0) Other 5 2 (40.0) Ductal lobular (0.6) Tubular 84 1 (1.2) Apocrine (40.3) Papillary 45 9 (20.0) Tubulolobular 30 Adenoid cystic (90.9) (76.9) Micropapillary 20 1 (5.0) Multifocality Monofocal (9.5) Multifocal (5.5) In Situ Component Absent (9.6) Present (5.9) Tumor Size 1 cm (5.3) 1-2 cm (8.2) 2-5 cm (12.7) 5 cm (7.8) Missing (14.5) Number of Positive Nodes None (9.9) (6.9) (8.2) (9.5) pnx (6.4) Clinical Breast Cancer February 2013

3 Emilia Montagna et al Table 1 (continued) All Breast Cancers Triple Negative (%) P Value Grade G (1.0) G (2.5) G (23.6) Missing (6.3) Peritumoral Vascular Invasion Absent (9.5) Present (6.9) Proliferative Fraction (Ki-67) 14% (1.8) 15%-30% (3.7) 30% (25.2).0002 Abbreviation: pnx unknown pathological Nodal status. factors. 6 In particular, histologic subtypes might play a role in the outcome. Literature data indicate that the diagnosis of special types of breast cancer might be associated with a different outcome if compared with IDC with similar biological features and stages. 7,8 The recognition of certain special types of invasive breast carcinoma might allow the identification of women with extremely good or extremely poor prognoses and may have therapeutic consequences. 9 To further unveil the prognostic significance of special types of primary breast cancer, we analyzed data from a large series of wellcharacterized patients with TNBC. Patients and Methods We extracted information from our prospectively collected institutional database on all consecutive patients with breast cancer surgically treated at the European Institute of Oncology between January 1997 and December Data on the patient s medical history, concurrent diseases, type of surgery, pathologic evaluation, and results of staging procedures were entered. Pathologic assessment included evaluation of the primary tumor size, histologic type, and lymph node status, including a sentinel lymph node biopsy when applicable. 10 The criteria used to define the histologic types studied in the present analysis were derived from the World Health Organization classification scheme. 11 Tumor grade, peritumoral vascular invasion, ER and PR status, Ki-67 labeling index (LI), and HER2 overexpression and/or amplification were evaluated as previously reported. 12 Tumor grade was evaluated according to Elston and Ellis. 13 Immunohistochemical staining for the localization of ER and PR, HER2 protein, and Ki-67 antigen was performed on consecutive tissue sections from the tumor-containing blocks. The following primary antibodies were used: the monoclonal antibody (mab) to ER (clone 1D5; Dako, Glostrup, Denmark at 1:100 dilution), the mab to PR (clone 1A6, Dako, at 1:800 dilution), the MIB-1 mab to the Ki-67 antigen (Dako, 1:100 dilution), and the polyclonal antibody (Dako, 1:3200 dilution) to the HER2 protein. Only nuclear reactivity was taken into account for ER, PR, and the Ki-67 antigen, irrespective of the staining intensity, whereas only an intense and complete membrane staining in 10% of the tumor cells qualified for HER2 overexpression (3 ). The fluorescence in situ hybridization assay for HER2 was performed in selected cases (especially those with 2 immunoreactivity) according to the manufacturer s instructions. A HER2-CEP17 ratio greater than 2.0 qualified for gene amplification. The results for ER, PR, and Ki-67 LI were recorded as the percentage of immunoreactive cells up to 2000 neoplastic cells. Steroid hormone receptor status was classified as negative in the case of lack of any ER and PR immunoreactivity or 1% immunoreactive tumor cells. A subtype classification has been adopted based on the immunohistochemical definition of estrogen and progesterone receptors, the detection of overexpression and/or amplification of the HER2 oncogene, and Ki-67 LI. 14,15 A tumor was considered triple negative when both ER and PR were negative and HER2 was not amplified or overexpressed. The cases were evaluated independently by 2 of the pathologists, and to ensure intraobserver and interobserver reliability 5% of cases were blindly reassessed by the same pathologist and 10% were reassessed by a different pathologist. If the evaluation differed, collegial reassessment at the multiheaded microscope was performed to obtain agreement; this occurred for about 1.2% of tumors. The study was approved by the institutional ethics committee. Statistical Analysis The Fisher exact test and the Mantel-Haenszel 2 test for trend were used to assess the association between, categorical and ordinal variables, respectively. The primary endpoint was disease-free survival (DFS). The secondary endpoint was overall survival (OS). DFS was defined as the time from definitive surgery to any event related to breast cancer (local or regional relapse, distant metastasis, contralateral breast cancer, or death, whichever occurred first). OS was determined as the time from surgery until the date of death from any cause. Active follow-up was conducted Clinical Breast Cancer February

4 Special Types of Triple-Negative Breast Cancer Table 2 Characteristics of Triple-Negative Breast Cancers According to Histologic Subtype All Triple Negative Ductal Lobular Apocrine Adenoid Cystic Other Subtypes All Age (y) Menopausal Status Premenopausal Postmenopausal Perimenopausal Multifocality Monofocal Multifocal In Situ Component Absent Present Tumor Size 1 cm cm cm cm Missing Number of Positive Nodes None pnx Grade G G G Missing Peritumoral Vascular Invasion Absent Present Proliferative Fraction (Ki-67) 14% %-30% % P Value Abbreviation: pnx unknown pathological Nodal status. to determine patient status as of October Surviving patients were censored at the date of last follow-up. Survival plots according to subtype were drawn using the Kaplan-Meier method. The log-rank test was used to assess the survival difference between strata. Multivariate Cox proportional hazard regression analysis was used to assess the independent prognostic significance of his- 34 Clinical Breast Cancer February 2013

5 Emilia Montagna et al topathologic subtypes of the tumor on DFS or OS. All analyses were performed with SAS software, version 8.2 (SAS Institute, Cary, NC). All tests were 2-sided and P values.05 were considered statistically significant. Treatment Received All patients received breast-conserving surgery or total mastectomy, plus axillary sentinel lymph node biopsy or complete axillary dissection. 10 Systemic adjuvant chemotherapy was recommended in accordance with the available St. Gallen treatment guidelines Anthracycline-containing chemotherapy for 4 cycles (ie, doxorubicin and cyclophosphamide) followed by 3 cycles of classic CMF (oral cyclophosphamide, methotrexate, and fluorouracil) was considered as the first option in patients with higher risk (ie, node-positive disease, young age); 19 in the case of comorbidities, lower risk (ie, node-negative disease) or patient preference, classic CMF for 6 courses was considered. 20 Results All consecutive women operated on for breast cancer at the European Institute of Oncology were referred for interdisciplinary evaluation and their data were included in the institutional database. The current study was limited to 8801 women with first primary nonmetastatic breast cancer treated between January 1997 and December 2005 who did not receive neoadjuvant chemotherapy and for whom characterization of triple-negative subtype was possible (ie, with evaluation of ER, PR, and HER2). The study population included 781 patients with TNBC. The overall distribution of TNBC according to histologic subtype is shown in Table 1. Tumors from 693 patients (89%) were classified as ductal not otherwise specified (NOS) (IDC), 29 (3.7%) were classified as apocrine, 18 (2.3%) were classified as lobular, 10 (1.2%) were classified as adenoid cystic, 10 (1.2%) were classified as metaplastic, 9 (1.1%) were classified as papillary, 4 (0.5%) were classified as medullary, and 10 (1%) were classified as very rare ( 0.5%) histotype (mucinous, cribriform, mixed, micropapillary) carcinoma. The median follow-up was 5.8 years (maximum, 13 years). The main characteristics of TNBC according to histologic subtype are reported in Table 2. Negative lymph node involvement was reported for all adenoid cystic carcinomas, for 64% of invasive ductal carcinomas (IDCs), for 60% of metaplastic carcinomas, for 55% of apocrine carcinomas, and for 44% of invasive lobular carcinomas (ILCs). All metaplastic subtypes were classified as high grade. IDC tumors were more frequently of higher grade (88%) than were other histologic subtypes (ILC, 44%; apocrine, 24%; adenoid cystic, 2%). A Ki-67 LI of more than 30% was encountered in 81% of IDCs and 50% of metaplastic cancers, whereas only 10% of adenoid cystic carcinoma showed a high proliferative fraction. Treatment Local treatments and systemic adjuvant therapies received by all 781 patients with TNBC are shown in Table 3. A total of 665 (85%) patients underwent conservative surgery and 510 (65%) had sentinel lymph node biopsies. The majority of the patients (44%) received adjuvant systemic chemotherapy with CMF, whereas 36% of the patients received an anthracycline combination. Table 3 Variable Surgical and Adjuvant Treatment of 781 Women with Triple-Negative Breast Cancer According to Lymph Node Involvement All n % All 781 (100.0) Type of Surgery Quadrantectomy 665 (85.1) Mastectomy 116 (14.9) Sentinel Lymph Node Biopsy No 271 (34.7) Yes 510 (65.3) Chemotherapy Anthracycline 280 (35.9) CMF 341 (43.7) Other/NOS 67 (8.6) None 93 (11.9) Radiotherapy None 106 (13.6) ELIOT 125 (16.0) External RT 550 (70.4) Abbreviations: CMF cyclophosphamide, methotrexate, and fluorouracil; ELIOT intraoperative electron-beam radiotherapy; NOS not otherwise specified; RT radiotherapy. Events Figure 1 shows the DFS and OS in each subtype. The 5-year DFS was 77% for patients with TNBC, 68% for the HER2-positive group, and 84% and 95% for patients with luminal B and luminal A breast cancer, respectively. Five-year OS was 83% in patients with TNBC and HER2-positive breast cancer and 94% and 98% in luminal B and luminal A subtypes, respectively. Figure 2 shows the DFS according to each histologic subtype of the TNBC group. Five-year DFS was 56% in patients with metaplastic tumors. Conversely, 5-year DFS for patients with adenoid cystic and medullary subtypes was 100%. Figure 2 shows the OS according to each histologic subtype in the TNBC group. The 5-year OS was 84% for patients with IDC, 82% for patients with ILC, 88% for patients with metaplastic disease, 92% for patients with apocrine subtype, and 100% for patients with adenoid cystic and medullary carcinoma. Univariate Analysis Compared with patients with IDC, DFS and OS were better for patients with adenoid cystic and medullary subtypes (log-rank P.04 and P.08, respectively), although results are based on a small number of cases. Conversely, DFS was worse for patients with metaplastic carcinomas (hazard ratio [HR], 1.56; 95% CI, ). Patients with metaplastic carcinoma had a poorer OS (HR, 1.60; 95% CI, ), although it was not significant (Table 4). Clinical Breast Cancer February

6 Special Types of Triple-Negative Breast Cancer Figure 1 (A, B) Outcome in Women With Breast Cancer According to Molecular Subtype A Disease free survival B Overall survival 100 Luminal A 80 Luminal B Triple neg Her2+ 60 Luminal A Luminal B Triple neg Her N o at risk Log-rank P =.0001 Log-rank P = Years Years N o at risk Luminal A Luminal B Her Triple neg Proportion free of events (95% CI) 1-year 2-year 5-year 10-year Luminal A 99.5 ( ) 98.8 ( ) 94.9 ( ) 85.5 ( ) Luminal B 98.5 ( ) 94.9 ( ) 84.0 ( ) 70.2 ( ) Her ( ) 82.9 ( ) 68.2 ( ) 59.7 ( ) Triple neg ( ) ( ) ( ) ( ) Luminal A Luminal B Her Triple neg Proportion surviving (95% CI) Luminal A Luminal B Her2+ Triple neg 1-year 2-year 5-year 10-year ( ) ( ) ( ) ( ) 99.8 ( ) 99.6 ( ) 99.1 ( ) 99.1 ( ) 96.8 ( ) 94.7 ( ) 94.7 ( ) 83.4 ( ) 83.2 ( ) 84.5 ( ) 69.3 ( ) 77.1 ( ) Abbreviations: HER 2 human epidermal growth factor receptor positive; Triple neg triple negative. Discussion Chemotherapy is the mainstay of systemic treatment for patients with TNBC, and identifying groups of patients to be candidates for specific treatment programs continues to represent a major research issue. The recognition of certain special types of invasive breast carcinoma might allow women with extremely good or extremely poor prognoses to be identified, with relevant therapeutic consequences. This issue was recently evaluated in a large series of patients with endocrine-responsive breast cancer; it was reported that the diagnosis of tubular, cribriform, and lobular carcinomas carries distinct prognostic implications in luminal breast cancers subtypes. 9 TNBC makes up about 15% of all subtypes of breast cancer and the relative rarity of special subtypes within cases of TNBC render them difficult to study. 5 The present study is based on a high accrual over a short period (ensuring similar clinical management), consistent pathologic reporting in a single institution (with prospectively collected and quality-controlled databases), and prolonged follow-up. It is unique in evaluating the outcome of special types of breast cancer within the subgroups of TNBC. We reported a different outcome for different subtypes of TNBC, indicating that TNBC encompasses several biological entities. Compared with IDC, each histologic special type might be driven by a less diverse constellation of genetic and epigenetic events, indicating that special types are relatively homogeneous at the genomic transcriptomic levels. 21,22 More frequently than in IDC, a histologic special type pertains to only 1 molecular subtype: Tubular and mucinous subtypes display a luminal subtype, whereas adenoid cystic, medullary, and metaplastic carcinomas display a basal-like phenotype. The specific molecular features of each special type could explain the different reported outcomes. In our study, patients with metaplastic breast cancers had poor DFS and OS, according to the results by Weigelt et al. 23 This rare special type of breast cancer is characterized by the appearance of squamous or (pseudo)sarcomatous features. 23 The understanding of molecular alterations and the genetic basis of metaplastic breast cancer is not complete. By microarray analysis, the molecular characteristics of metaplastic breast cancers were investigated. breast cancer shows a downregulation of genes involved in DNA repair and response to chemotherapy. 24 The levels of topoisomerase II alpha and PTEN are 36 Clinical Breast Cancer February 2013

7 Emilia Montagna et al Figure 2 (A) Disease-Free Survival and (B) Overall Survival of Women With Triple-Negative Breast Cancer According to Selected Histologic Subtypes A Disease free survival B Overall survival 100 Adenoid cystic 100 Medullary 90 Medullary 80 Apocrine 90 Papillary 70 Ductal Papillary Apocrine Lobular 50 Ductal 40 Lobular Log-rank P = Log-rank P = Years Years N o at risk Ductal N o at risk Ductal Lobular Lobular Apocrine Apocrine Papillary Papillary Adenoid cystic Adenoid cystic Medullary Medullary Ductal Lobular Apocrine Papillary Adenoid cystic Medullary ** at 7-year Proportion free of events (95% CI) Proportion surviving (95% CI) 1-year 2-year 5-year 10-year 1-year 2-year 5-year 10-year 95.0 ( ) 87.8 ( ) 77.3 ( ) 66.9 ( ) Ductal 99.1 ( ) 94.3 ( ) 84.1 ( ) 76.3 ( ) ( ) ( ) 64.3 ( ) 83.7 ( ) ( ) 45.9 ( ) 67.0 ( ) ( ) 55.7** ( ) Lobular Apocrine Papillary Adenoid cystic Medullary ( ) ( ) ( ) 81.9 ( ) ( ) ( ) 57.1** ( ) frequently low, the BRCA1 pathways are dysfunctional, and the BRCA1 gene is downregulated by promoter methylation. 25 Conversely, in metaplastic breast cancers the genes associated with adhesion, motility, and migration are upregulated. The upregulation of the extracellular matrix-related genes could account for the sarcomatous morphologic features. 26 The identification of genes differentially expressed in metaplastic breast cancer could explain the resistance to cytotoxic agents and the generally poor outcome with a high risk of recurrence, even if good prognosis is reported for low-grade metaplastic tumors such as the fibromatosis-like variant and the lowgrade adenosquamous carcinomas. In contrast to metaplastic breast cancer behavior, we reported an excellent prognosis for the classic medullary and adenoid cystic carcinomas, according to previous experiences. 21 The favorable outcome of medullary cancers could also be explained by gene expression profiling analysis. In fact medullary breast cancer shows upregulation of genes involved in the immune response, suggesting the implication of TH1 cells and a likely high global cytotoxic activity. 27 Moreover, Bertucci et al reported that members of the tumor necrosis factor (TNF) receptor gene family and of the TNF ligand superfamilies, involved in the extrinsic apoptosis pathway, are overexpressed in medullary breast cancer. 28 Several downregulated genes instead are involved in the architecture and remodeling of cytoskeleton. These genes encode actins, myosin light chain (MYL9), -tropomyosin, and several regulators or associated proteins. Moreover, several genes encoding receptors involved in cell invasiveness and genes involved in cell adhesion are downregulated in medullary breast cancers. 28 Histologically, adenoid cystic carcinoma is characterized by invasive proliferation of circumscribed clusters of cells forming solid, cribriform, tubular, and trabecular arrangements with 1 pattern that Clinical Breast Cancer February

8 Special Types of Triple-Negative Breast Cancer Table 4 Univariate And Multivariate Analysis Disease-Free Survival Overall Survival Univariate Multivariate a Univariate Multivariate a HR (95% CI) HR (95% CI) HR (95% CI) HR (95% CI) Ductal Lobular 1.54 ( ) 1.43 ( ) 0.85 ( ) 1.04 ( ) Apocrine 0.92 ( ) 0.90 ( ) 0.56 ( ) 0.87 ( ) Papillary 1.17 ( ) 1.29 ( ) 0.54 ( ) 0.65 ( ) Adenoid Cystic 1.56 ( ) 1.50 ( ) 1.60 ( ) 1.02 ( ) Medullary Abbreviations: CI confidence interval; HR hazard ratio. a Adjusted for age, presence of in situ component, multifocality, tumor size, number of positive nodes, tumor grade, peritumoral vascular invasion, and Ki-67. can predominate. It is characterized by 2 distinct cell populations epithelial and myoepithelial cells. The biological mechanisms underlying the favorable behavior of adenoid cystic carcinoma of the breast have yet to be elucidated. 29 However the downregulation of genes related to cell migration and proliferation and the low histologic grade could be involved in the favorable outcome of adenoid cystic carcinomas. 30 In the present analysis, apocrine carcinomas show similar outcome if compared with ductal carcinomas. Similarly Takeuchi et al reported no difference in survival rates at 10 years after operation between apocrine carcinoma and nonapocrine carcinoma. 31 Moreover, in a subgroup of apocrine carcinoma, the presence of androgen receptor, as well the expression of epithelial growth factor receptor (EGFR), could be involved in the clinical behavior of the disease. 31 The molecular differences reported in the special type of TNBC may translate into different therapeutic approaches. Most recently, systemic treatment recommendations suggested that medullary and adenoid cystic carcinomas may not require any adjuvant cytotoxic agents if the nodes were negative. 15 Our results support this approach because nonevents were registered in patients with medullary carcinoma and in patients with adenoid cystic breast cancer. Conversely, new chemotherapeutic drugs should be considered in the treatment of metaplastic subtypes to overcome the resistance to cytotoxic agents, although the rarity of the disease complicates the possibility of conducting studies in this patient population. Moreover, the understanding of the molecular heterogeneity of special-type TNBC has led to the development of new potential therapeutic targets. The pathway of DNA damage response (ie, the development of poly(adp- ribose) polymerase inhibitors, the use of alkylating agents) as well as angiogenesis or epithelial/mesenchymal transition and immune deregulation and EGFR could offer a potential target for drug development. 32,33 In conclusion, the results of the present study indicate that there is a need to tailor the approach within the heterogeneous triple-negative subtypes. An accurate and reliable histopathologic assessment provides a key to detect special types of cancer with particular regard to the need for adjuvant systemic treatment. The definition of specific niches for tailored research through international cooperation is crucial to make progress and to solidify consensus on how to treat individual patients with special types of breast cancer. Clinical Practice Points TNBC is a heterogeneous disease. Histologic subtypes might play a role in the outcome in TNBC. The recognition of certain special types of invasive breast carcinoma might allow the identification of women with an extremely good or extremely poor prognosis and may have therapeutic consequences. Our study population included 781 patients with TNBC; we explored the outcome in terms of DFS and OS. Tumors from 693 patients (89%) were classified as ductal NOS (IDC), 29 (3.7%) were classified as apocrine, 18 (2.3%) were classified as lobular, 10 (1.2%) were classified as adenoid cystic, 10 (1.2%) were classified as metaplastic, 9 (1.1%) were classified as papillary, 4 (0.5%) were classified as medullary, and 10 (1%) were classified as of very rare ( 0.5%) histotype (mucinous, cribriform, mixed, micropapillary) carcinoma. Compared with patients with invasive IDC, DFS and OS were better for patients with adenoid cystic and medullary subtypes, although results are based on a small number of cases. Conversely, DFS was worse for patients with metaplastic carcinomas. Patients with metaplastic carcinoma had poorer OS, although it was not significant. Compared with IDC, each histologic special type might be driven by a less diverse constellation of genetic and epigenetic events. The specific molecular features of each special type could explain the different reported outcome and may translate into different therapeutic approaches, leading to the development of new potential therapeutic targets in patients with TNBC. Acknowledgments We wish to thank the patients, nurses, and physicians at the European Institute of Oncology. We thank William Russell-Edu for his assistance with the manuscript. 38 Clinical Breast Cancer February 2013

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