Combination Therapy for Childhood Acute Lymphocytic Leukemia

Transcription

1 Rhomes J. A. Aur, MD*, Kwesi Sackey, MB ChB, Rajeh S. Sabbah, MD, Samira Rifai, MD, J. Trenholme Griffin, MD, Mustapha Ghandour, MD, Flynn Warren, MS *Head, Division of Pediatric Oncology, Department of Oncology; Junior Staff, Division of Pediatric Oncology; Department of Oncology; Chairman, Department of Oncology; Radiation Therapist, Department of Oncology; Chairman, Department of Pediatrics; Head, Pharmacy Services, King Faisal Specialist Hospital and Research Centre, Riyadh 11211, Saudi Arabia Parts of this work were presented at the 8th Saudi Medical Conference from 30 October 3 November 1983, at the King Khalid Military Academy, Riyadh, Kingdom of Saudi Arabia ABSTRACT This study for previously untreated childhood acute lymphocytic leukemia, conducted from April 1981 to November 1983, included 91 patients divided in two distinct groups, according to clinical and laboratory features at diagnosis. The standard risk group consisted of 64 patients, while the high risk group had 27 patients. The therapy differed according to the risk group. The following are the results for the standard risk and high risk groups, respectively: (1) early death rate, 7.8% and 26%; (2) induction of complete marrow remission, 97% and 90%; (3) incidence of CNS leukemia, 16% and 25%; and (4) overall relapse rate, 49% and 78%. These results indicate that, for the standard risk patients, the degree of success is parallel to current results from most series, and that the failure rate for the patients in the high risk group is extremely high. Early deaths may be avoided by prompt treatment and by an increase in the intensity of therapy to the highest tolerable levels for the patients with high risk features. Attempts to improve the outcome also for standard risk patients may be carried out through changes in therapy, aiming at enhancing their chances for leukemia-free survival. RJA AUR, K SACKEY, RS SABBAH, S RIFAI, JT GRIFFIN, M GHANDOUR, F WARREN, Combination Therapy for Childhood Acute Lymphocytic Leukemia. 1985; 5(2): KEYWORDS: Leukemia, lymphocytic In infancy and childhood Leukemia, lymphoblastic In infancy and childhood Introduction Acute lymphocytic leukemia (ALL) is the most common malignancy affecting children. As a drug-responsive neoplasm, ALL has been a testing ground for the development of concepts in cancer therapy that have broad potential application. Dr. Sidney Farber made a breakthrough in the treatment of this dreadful disease in 1948 when he demonstrated that childhood ALL was responsive to aminopterin. 1 In the following decade other drugs were used with partial success. The remissions obtained were temporary, and the disease followed a fatal course in a short period of time. In 1962 an all-out combat against ALL was initiated utilizing the concept of "Total Therapy", the combination of all known effective agents given for induction of remission, intensification of remission, and maintenance of remission. 2 In less than two decades childhood ALL has been changed from a uniformly fatal disease to one curable in nearly one half of cases. 3 This paper contains the three-year preliminary results of a protocol devised for the treatment of children with ALL, previously untreated, in the Kingdom of Saudi Arabia. Methods Definitions A diagnosis of ALL is made when lymphoblasts or stem cells predominate in the bone marrow. In effect, childhood leukemia is considered lymphocytic unless cells are characterized by unequivocal Auer rods and/or definite morphological and cytochemical features of myelocytic, monocytic, or histiocytic differentiation. By these criteria, approximately 80% of childhood leukemia is classified as acute lymphocytic leukemia. Patients with >25% lymphoblasts in the initial marrow were eligible for this protocol. A complete remission bone marrow is defined as a cellular marrow demonstrating satisfactory hematopoiesis and containing 5% or less lymphoblasts plus stem cells. A hypocellular marrow specimen containing mainly peripheral blood cells is considered unsatisfactory and not a remission marrow. A partial remission marrow is one

2 that contains 5% to 25% lymphoblasts or 40% to 70% lymphocytes plus lymphoblasts. A complete relapse bone marrow is one that contains more than 25% lymphoblasts or more than 75% lymphocytes plus lymphoblasts. A complete remission means the patient is free from symptoms and physical findings attributable to leukemia, the peripheral blood contains 500 cells/mm 3 or more neutrophils and 75,000 cells/mm 3 or more platelets, and the marrow demonstrates complete remission status. Granulocytopenia and thrombocytopenia, obviously secondary to therapy and reversible by dosage adjustment, do not signify the termination of remission. Relapse is defined as the reappearance of leukemia as manifested by a partial remission marrow persistent or progressive to a relapse marrow, or by appearance of central nervous system (CNS) leukemia, visceral infiltration, or any symptoms or signs definitely attributable to leukemia. Complete remission duration is the time between the first complete remission marrow and the first sign of relapse, whether hematologic, nervous system, or visceral. Hematologic remission duration is the time between the first complete remission marrow and first evidence of marrow relapse. Thus, hematologic remission duration includes periods with leukemia in the CNS or other sites outside the marrow. Time to central nervous system leukemia is the period between the first complete remission marrow and the first evidence of CNS leukemia. Survival is the period between diagnosis of leukemia and death. It should be emphasized that complete remission duration refers to the initial continuous remission, free of all evidence of leukemia, and that hematologic remission duration refers to the initial continuous remission, free of hematologic evidence of leukemia. Early death refers to a patient dying within the first month from diagnosis and not receiving a full induction course of therapy. Evaluation of the patients Confirmation of the diagnosis of ALL always preceded the institution of specific therapy. The initial evaluation included: physical examination and anthropometric values, peripheral blood, bone marrow (morphology and cytochemistry) and cerebrospinal fluid (CSF) examinations, routine blood chemistries and urinalysis, bacterial and fungal studies of secretions from the mouth, pharynx, urine, stools, blood, bone marrow, and CSF in febrile patients, as well as culture of infected lesions, no matter how minor the lesions. Chromosome studies and determination of cell membrane markers were not carried out routinely. Radiographs of the chest were obtained routinely. Other studies such as x-rays of bones, faciocranial sinus series, CT scan of brain, and ultrasound of abdomen were done according to clinical indication. All pertinent analyses and studies were repeated according to the phase of therapy. Fine needle aspiration biopsy of the testicles was performed at the end of therapy for consideration of stopping all therapy. The clinico-laboratory parameters at diagnosis for risk group allocation were peripheral white blood cell (WBC) count, CNS leukemia, and mediastinal mass. Standard risk group included patients with peripheral WBC count 100,000/mm 3 or less, and absence of both CNS leukemia and mediastinal mass. High risk group included patients with one or more of the above features. The presence of CNS leukemia was determined by the presence of leukemic blasts, regardless of number, in the cerebrospinal fluid (CSF); and the presence of thymic infiltration was determined on plain chest x-rays. Patients with B-cell ALL were by design of the protocol allocated to the high risk group. A diagnosis of testicular leukemia is proved when leukemic cells are found in tissue sample obtained through percutaneous fine needle aspiration or surgical biopsy. Outline of Therapy For standard risk patients, induction of remission consisted of prednisone, vincristine, and daunomycin, plus methotrexate intrathecally for four to six weeks. This was followed by preventive CNS therapy with 1800 rad cranial irradiation and simultaneous intrathecal methotrexate for two and a half weeks plus mercaptopurine; this was followed by maintenance therapy with methotrexate and mercaptopurine with pulses every three months of vincristine and cyclophosphamide, alternating with prednisone, vincristine, and Adriamycin for two years (Table 1).

3 Table 1. Outline of therapy for standard risk group Phase I: Remission induction (4 to 6 weeks) PO prednisone 40 mg/m 2 /day IV vincristine 1.5 mg/m 2 /week (maximum dose 2.0 mg) IV daunomycin 2.5 mg/m 2 /week IT methotrexate 12 mg/m 2 /dose (maximum dose 12 mg) at diagnosis, at day 29, and (if remission induction is extended to 6 weeks) on day 42. Phase II: Preventive central nervous system therapy (2½ weeks) IT methotrexate 12 mg/m 2 /dose 4 injections (maximum dose 12 mg) twice a week, simultaneously with 1800 rad cranial irradiation.* PO mercaptopurine 50 mg/m 2 /day Phase III: Maintenance chemotherapy (24 months) (1) For three months: PO mercaptopurine 50 mg/m 2 /day PO methotrexate 25 mg/m 2 /week (2) After each three months, withhold mercaptopurine and methotrexate and give alternating two-week pulses of: (a) IV vincristine 1.5 mg/m 2 /week 3 doses (maximum dose 2.0 mg) IV cyclophosphamide 300 mg/m 2 /week 3 doses (b) PO prednisone 40 mg/m 2 /day 14 days IV vincristine 1.5 mg/m 2 /week 3 doses (maximum dose 2.0 mg) IV Adriamycin 40 mg/m 2 /single dose * For children over the age of two years For high risk patients, remission induction consisted of prednisone, vincristine, Adriamycin, and cyclophosphamide plus intrathecal methotrexate for four to six weeks, followed by methotrexate and mercaptopurine maintenance. During the first year, central nervous system prophylaxis consisted of intrathecal methotrexate monthly and pulses of intravenous intermediate dose methotrexate every three months for four courses. This was followed at the one year mark by 2400 rad cranial and 1800 rad spinal radiation over a period of four weeks. Further maintenance consists of an additional 12 months of methotrexate and mercaptopurine with pulses of vincristine and cyclophosphamide, alternating with prednisone, vincristine, and Adriamycin for one year, similar to that for patients in the standard risk group in order to complete two years of maintenance therapy (Table 2). Table 2. Outline of therapy for high risk group Phase I: Remission induction (4 to 6 weeks) PO prednisone 40 mg/m 2 /day IV vincristine 1.5 mg/m 2 /week (maximum dose 2.0 mg) IV Adriamycin 40 mg/m 2 /every other week (alternating with cyclophosphamide) IV cyclophosphamide 450 mg/m 2 /every other week (alternating with Adriamycin) IT methotrexate 12 mg/m 2 /dose (maximum dose 12 mg) at diagnosis day 29, and (if remission induction is extended to 6 weeks) day 42. NOTE: For children with initial CNS leukemia, IT methotrexate 12 mg/m 2 /dose (maximum dose 12 mg) weekly throughout the remission induction phase. Phase II-A: Preventive central nervous system therapy (for the first 12 months) IT methotrexate 12 mg/m 2 /every 4 weeks (maximum dose 12 mg)

4 IV methotrexate 500 mg/m 2 with Citrovorum Factor rescue, and IT methotrexate 12 mg/m 2 /dose (maximum dose 12 mg) every 3 months for four courses. Phase II-B: Maintenance chemotherapy for the first 12 months PO 6-mercaptopurine 50 mg/m 2 /day PO methotrexate 25 mg/m 2 /week (omitted during IV + IT methotrexate course) Phase III: Central nervous system therapy (4 weeks) At the end of 12 months, craniospinal irradiation is given (2400 rad/1800 rad, respectively) Phase IV: Maintenance chemotherapy for the second 12 months As outlined for the standard risk group, Table 1, Phase III Patients failing to attain remission in six weeks received asparaginase and Ara-C for two to four weeks. If failure persisted, the patients received VM-26 and Ara-C for two to four weeks (Table 3). Preventive CNS irradiation was begun immediately following completion of induction therapy if complete remission was achieved. A cobalt 60 unit or linear accelerator was used to administer 1800 rad to the midplane of the skull in 12 fractions over a period of 18 days. Cranial irradiation was given through opposing lateral portals including the retro-orbital space and the first two cervical vertebrae. The first dose of intrathecal methotrexate in this phase was given at the end of the remission induction phase and subsequent doses every 3 to 4 days thereafter until four doses had been given. The last dose of methotrexate usually coincided with completion of cranial irradiation. Table 3. Back-up chemotherapy for patients failing to achieve remission in the first six weeks Schedule 1: Simultaneous IV Ara-C: 300 mg/m 2 /twice a week 4 to 8 doses IV asparaginase; 10,000 units/m 2 /twice a week 4 to 8 doses (If failure occurs again:) Schedule 2: Simultaneous IV VM-26: 165 mg/m 2 /twice a week for 4 to 8 doses IV Ara-C: 300 mg/m 2 /twice a week for 4 to 8 doses Schedule 3: Contingency plans for extramedullary relapses during maintenance phase CNS leukemia: IT methotrexate 12 mg/m 2 /week 4 to 6 doses then monthly if patient achieves a second complete remission Testicular leukemia (biopsy proved): Radiotherapy to the involved testicle(s) 2000 rad (10 fractions) For prevention of CNS leukemia for high risk patients, or for therapy of CNS leukemia, the cranium receives 2400 rad given in 14 fractions over a period of 24 days and through portals including the cervical spine, and the spine is treated through posterior fields interlacing at portal junctions. Dosage of spinal irradiation is limited to 1800 rad given as 14 fractions over a period of 24 days. The principal guideline of maintenance therapy is maintenance of the leukocyte count between 2000 and 3500/mm 3 with an absolute neutrophil count of at least 500/mm 3. The prescribed dosages in Tables 1 and 2 are starting points only and are increased or decreased to suit each individual's tolerance. If therapy is interrupted due to infection or severe leukopenia (less than 1000 cells/mm 3 ), all agents are stopped. If the leukocyte count is persistently above 3500/mm 3, the dosage of all agents is increased by 25%. The only exception to uniform adjustment of dosage is interruption of cyclophosphamide therapy due to hemorrhagic cystitis. All therapy is scheduled to be discontinued after 24 months of continuous complete remission or 12 months of the second complete remission following treatment for isolated extramedullary relapse (Table 3). For patients in the standard risk group who develop CNS leukemia after receiving preventive CNS therapy (Table 1), induction of CNS remission is attempted with intrathecal methotrexate (Table 3). If continuous marrow remission is secured for a minimum of two years and CNS remission is sustained for a minimum of one year, a second course of CNS irradiation is given (Table 2, Phase III) prior to cessation of therapy.

5 Patients In the standard risk group and the high risk group respectively, 64 and 27 patients entered the study between April 1981 and November Among the 64 standard risk patients, 40 were boys. Their ages ranged from six months to 13 years (median: 4.5 years). The initial WBC count varied from 800 to 100,000/mm 3 (median: 6700/mm 3 ). Of the 27 high risk patients, 17 were boys. Their ages ranged from 1 to 13 years (median: 5 years). The initial WBC count (Table 4) ranged from 2600 to 775,000/mm 3 (median: 113,000/mm 3 ). The occurrence of elevated WBC count, CNS leukemia, and thymic involvement among the 27 patients in the high risk group is shown in Table 4. One patient presented with bilateral testicular leukemia and WBC count of 153,000/mm 3. Two patients with B- cell ALL were enrolled in the high risk group. Most of the patients were gravely ill due to extensive disease and prolonged time interval between the onset of disease and referral for treatment. Table 4. Initial features of the 27 patients in the high risk group WBC over 100,000 mm 3 9* CNS leukemia 5 Mediastinal mass 3 WBC + CNS leukemia 0 WBC + mediastinal mass 5 Mediastinal mass + CNS leukemia 3 B-cell ALL 2 * One patient had bilateral testicular leukemia at diagnosis and died early. Results The clinical outcome of patients in either risk group is shown in Table 5. Early deaths during the induction of remission phase were counted as therapy failure despite the fact that the therapeutic trial was incomplete. The remission rate was 89% (57/64) and 69% (18/27) for the standard risk group and the high risk group respectively. If only patients who completed the entire remission induction phase are considered, the complete remission rates for standard risk group and high risk group are 97% (57/59) and 90% (18/20) respectively. Table 5. Clinical outcome for 91 patients with childhood acute lymphocytic leukemia (ALL) from 1 April 1981 to 1 June 1984 Outcome Standard risk group (64 patients) High risk group (27 patients) Death during induction of 5 7 remission Induction failure 2 2 Relapses: Central nervous 10* 4 system (CNS) CNS + hematologic 7 1** Hematologic 9 9 Testicular 0 1*** Death in complete remission 2 0 Continuous complete remission 27 2 (CCR) Duration of CCR in 6 38(16) 9 15(7) months/range (median) Off therapy in CCR 6 0 Relapses off therapy in CCR 0 0 Continuous hematologic 33 4 (marrow) remission (CHR) Duration of CHR in months/ 6 38(20) 9 35(10) range (median) Off therapy in second complete 1 0

6 remission (CR) Relapses off therapy in second 0 0 CR Abandoned therapy in CCR 1 (5 mos) 2 (4 mos)**** Survivors 38 7 * At marrow remission date, one patient *** B-cell ALL *** At diagnosis **** B-cell ALL, one patient Of all children in the standard risk group who attained complete remission, six required extended therapy with asparaginase + Ara-C, and of these, two required the addition of VM-26 + Ara-C (Table 3). One patient had received asparaginase prior to referral to our institution. In spite of this deviation from the protocol, the child was enrolled in the study for full evaluation because the other three induction agents were given in similar dosages as shown in Table 1, Phase I. The mortality rates during the earliest phase of treatment were extremely high at 7.8% (5/64) and 26% (7/27) for standard risk group and high risk group, respectively. Deaths were due mostly to bacterial infections and candidiasis (Table 6). The most prevalent bacterial organism was Pseudomonas aeruginosa followed by Staphylococcus aureus, Clostridium species, and Klebsiella pneumoniae. Table 6. Fatalities during initial phase of therapy Standard Risk Group Case Age/ Year Sex No. Days from DX Cause 1 4 G 14 S. aureus sepsis Pseudomonas cellulitis 2 3 B 27 Systemic candidiasis 3 12 G 48 Refractory leukemia 4 4 G 7 Pseudomonas sepsis 5 2 G 14 Pseudomonas cellulitis E. coli cellulitis S. aureus cellulitis Candida cellulitis Candida tropicalis meningitis High Risk Group 1 13 B 14 Progressive leukemia 2 3 B 6 Pseudomonas sepsis 3 8 B 77 Refractory leukemia 4 2 G 15 Pseudomonas sepsis 5 1 G 14 Clostridium sepsis 6 3 G 24 Klebsiella sepsis Pseudomonas sepsis 7 4 B 2 Bacterial pneumonia Central nervous system leukemia terminated continuous complete remission in nine patients (16%) in the standard risk group in 11 to 24 months (median: 17 months, Tables 5 and 7). Of those, six have maintained their initial marrow remissions for 14 to 37 months, and one patient has been off therapy for three months (Patient 1, Table 7). Prior to stopping his therapy, he was given a second course of CNS irradiation as outlined in Table 2, Phase III. The boy who received asparaginase prior to referral developed CNS leukemia 22 months after attaining complete remission (Patient 5, Table 7). Central nervous system leukemia developed in four patients (25%) in the high risk group at 3,5, 7, and 11 months of continuous complete remission. Of these, two patients maintained the initial bone marrow remission for 14 and 35 months. The three patients who abandoned treatment while in continuous complete remission and the two patients failing to achieve complete remission following complete schedules listed in Tables 1, 2, and 3, are counted as treatment failures. Thus, the actual overall relapse rates for standard risk group and high risk group are 49% (28/57)

7 and 78% (14/18), respectively. Table 7. Central nervous system leukemia as initial relapse in standard risk group Time to CNS relapse (months) Time to hematologic relapse (months) Age Initial Case Sex (years) WBC 10 3 Outcome 1 B Off Rx 2 B Died 3 B Died 4 B Well 5 B Well 6 B Well 7 G Well 8 B Well 9 G Well The only two infants in this series (a girl six months and a boy 12 months of age) did not receive cranial irradiation because of their young age, which predisposes to more side effects. Instead they received intrathecal methotrexate, 12 mg/m 2 weekly for four weeks followed by a monthly injection for the duration of maintenance therapy. These infants relapsed in the bone marrow six months (boy) and 18 months (girl) after attaining initial complete remission. A two-year-old boy who had associated acute infantile hemiplegia also received preventive CNS therapy as outlined above. He has been off therapy for seven months. One child in the standard risk group died from acute hepatitis B at the end of remission induction phase in complete remission and before preventive CNS therapy was begun. Another child belonging in the same group died at home, after 17 months in continuous complete remission, from a sudden illness during maintenance therapy. The following life-threatening nonbacterial infections occurred during the period of remission in 11 patients: varicella (9), rubeola (1), and acute hepatitis A (1). Three of the patients with varicella required admission for intravenous Acyclovir because of pulmonary involvement. All 11 patients recovered from their disease without residua. Adverse effects expected from therapy and other less serious illnesses were easily controlled. Secondary malignancies have not been encountered thus far. The study period is short, and the likelihood for these complications to emerge at this point is low. Seizure activity related to preventive CNS therapy has not occurred. Testicular leukemia only occurred in one patient at diagnosis (Tables 4 and 5). Seven patients in the standard risk group have been off therapy and have remained well for an additional one to 14 months (Table 5 and one patient in Table 7). The clinical outcome regarding initial continuous remission and initial continuous marrow remission for patients in either risk group is depicted in Figs. 1 and 2. These graphic representations correspond to the numerical results expressed in Table 5. Discussion A number of drugs such as prednisone and vincristine, used as single agents, induce remission in about 50% of patients. Responses improve when drugs with different mechanisms of action are combined. Prednisone and vincristine used together induce remission in 90% of patients. 2, 3 The addition of a third drug, such as daunomycin or asparaginase, gives marginally superior results but carries extra toxicity. Since the intensity of initial remission induction therapy may affect a patient's chances for leukemia-free survival, the inclusion of prednisone, vincristine, and daunomycin has been a standard remission induction therapy since , 3 A fourth inducing agent, asparaginase, was added to prednisone, vincristine, and daunomycin in a selected group of patients with florid leukemia, who had been labeled as high risk for therapy failure. 4 These patients had one or more of the following clinico-laboratory characteristics: WBC count over 100,000/mm 3, presence of mediastinal mass and CNS leukemia, massive lymphadenopathy, and hepatosplenomegaly. 4, 5 Black children also fared less well under the same circumstances of treatment. 6 Age and sex as well as initial hemoglobin level and platelet count were also identified as risk factors Mediastinal mass has received a great deal of attention, and therapeutic trials have been specially designed to challenge its presence Mediastinal mass is usually associated with T-cell ALL as determined by the E + rosette formation test and detection of T-cell antigens.

8 Fig. 1. Duration of initial complete remission for the patients in the two risk groups (April 1981 June 1984). If the patients who died early and received insufficient induction therapy are excluded, the remission rates for our standard risk patients receiving the 3-drug-schedule and high risk patients receiving the 4-drug-schedule (Tables 1 and 2) were quite high: 97% and 90% respectively. The fact that the patients, as a rule, were quite ill at the time of referral accounts for induction death rates far above those reported in most series In early attempts to prevent CNS leukemia, 500 to 1200 rad craniospinal irradiation was given early in remission. However, the frequency of CNS leukemia was similar to that seen if no preventive therapy was given. 3, 4 The combination of 2400 rad cranial irradiation plus intrathecal methotrexate proved highly effective. 3, 4, The value of 2400 rad craniospinal irradiation to prevent CNS leukemia was also determined in a controlled fashion. Therefore, 2400 rad craniospinal irradiation and 2400 rad cranial irradiation plus simultaneous intrathecal methotrexate seemed equally effective for prevention of CNS relapse. 3, 4 In view of the concern that spinal irradiation might impair growth in height and limit marrow reserve, cranial irradiation plus intrathecal methotrexate was indicated as the preferred method of CNS preventive therapy. With this method, the likelihood of primary CNS relapse is 10% or less. 3, 4, However, this treatment has two potential disadvantages: (1) chronic CNS functional impairment does occur in some patients so treated; and (2) the delivery of cranial irradiation does limit the dosage of parenteral methotrexate one can safely administer during continuation therapy without inducing crippling leukoencephalopathy. 11 The dosage of 1800 rad cranial irradiation plus intrathecal methotrexate for standard risk patients has proved to be as effective as a 2400 rad dose and to be less toxic to the CNS The use of chemotherapy alone to prevent CNS leukemia has been studied by Freeman et al., 24 utilizing simultaneous intravenous intermediate dose methotrexate (500 mg/m 2 with one-third as a push dose and the remaining two-thirds as a 24-hour infusion) given three times at three-week intervals following the induction of remission. The results were superior to those seen in children receiving 2400 rad irradiation plus intrathecal methotrexate. Others who have attempted to control occult CNS disease with periodic intrathecal therapy alone have had comparable results and with less toxicity to the CNS. 20, 25, 26 The randomized study by the Children's Cancer Study Group 18 indicated clearly inferior results in the group of patients receiving intrathecal therapy as the sole form of prevention of CNS leukemia. Fig. 2. Duration of initial complete remission for the patients in the two risk groups (April 1981 June 1984).

9 In our series, CNS leukemia interrupted continuous complete remission in 16% and 25% of patients in standard risk group and high risk group, respectively. These figures, mainly those for the high risk group, are very high and indicate that the effectiveness of prevention of CNS leukemia, according to the design of the protocol, is inadequate. Intermittent methotrexate is the best of the single drugs and the only one that may yield long-term complete remissions by itself. When mercaptopurine, the second best single agent, is given daily and methotrexate weekly, the results are improved. Maintenance therapy which also included cyclophosphamide given on a weekly basis failed to render superior results in controlling leukemia, as did the addition of weekly Ara-C. 11 Short pulses of prednisone and vincristine throughout the maintenance phase were used but failed to show any added value. 2, 3 An effective alternative to administration of prednisone and vincristine pulses is the addition of Adriamycin during maintenance therapy as reported from the Sidney Farber Cancer Center. 27 The use of alternating pulse therapy during remission using prednisone, vincristine, and daunomycin/vincristine and cyclophosphamide, with a late intensification phase using VM-26 and Ara-C/asparaginase for a group of patients in St. Jude's "Total Therapy IX", failed to improve the outcome regarding disease-free survival. 12 Intensive use of asparaginase during the maintenance phase in children with non-t-cell ALL gave remarkable preliminary results with toxicity managed reasonably well. 28 The effectiveness of VM-26 + Ara-C during maintenance for patients with standard and high risk leukemia has been 23, 29 established. Hematologic relapse remained a formidable problem and occurred in 49% of the standard risk patients and in 78% of the high risk patients. The rate of relapse following cessation of therapy may reveal long-term beneficial effects from the use of the pulses during the maintenance phase. The intensive treatment program of combined therapy delivered for two to three years is immunosuppressive and leaves the patient vulnerable to opportunistic infections. As a result, an unfortunate 5% to 7% of children died while in remission. 30, 31 In fact, some multiple drug regimens were clearly inferior due to their associated higher risk of infections. 11 The two major culprits were Pneumocystis carinii pneumonia and disseminated varicella-zoster, each of which produced marked morbidity and significant mortality. 30, 31 Effective prophylaxis against Pneumocystis carinii, using a combination of trimethoprim and sulfamethoxazole (TMP-SMZ), alleviated the risk to which these children were subjected. 32, 33 It is important to point out that our patients are not placed on TMP-SMZ prophylaxis; Pneumocystis carinii pneumonitis has not been encountered among our patients. Thus far, our therapy seems to be effective in preventing testicular leukemia. There has not been any clinical involvement of the testes during maintenance therapy for the boys in either risk group. All boys, at termination of therapy (2 years), undergo bilateral percutaneous fine needle aspiration of the testicles. Isolated subclinical (or occult) testicular leukemia occurs in about 10% of the boys' biopsies at the end of therapy. 34 All seven patients off therapy are boys and all had negative biopsies. The almost universal practice has been to stop therapy electively for all patients who remain in continuous complete remission for 24 to 36 months. The overall relapse rate off therapy is 25% or less; it is highest in the first year after stopping therapy then drops to low levels and after three years is negligible The development of relapse indicates the emergence of cells that are resistant to the chemotherapeutic agents the patient is receiving or has received. The solution to the problem is to understand the biologic behavior of the leukemic cells and to introduce new chemical or biologic agents able to circumvent the appearance of refractory mutant cells. ACKNOWLEDGMENTS The authors wish to express their gratitude to Ms. Carol Duggar for her excellent typing assistance. REFERENCES 1. Farber S, Diamond LK, Mercer RD, et al: Temporary remissions in acute leukemia in children produced by folic acid antagonist, 4-aminopteroyl-glutamic acid (Aminopterin). N Engl J Med 238(23): Aur RJA, Sabbah RS, Sackey K: Different combined approaches in the treatment of childhood acute lymphocytic leukemia. The King Faisal Specialist Hospital Medical Journal 4(2): Pinkel D: The ninth annual David Karnofsky lecture. Treatment of acute lymphocytic leukemia. Cancer 43(3): Aur RJA, Simone JV, Pratt CB: Successful remission induction in children with acute lymphocytic leukemia at high risk for treatment failure. Cancer 27(6): Simone JV, Verzosa MS, Rudy JA: Initial features and prognosis in 363 children with acute lymphocytic leukemia. Cancer 36(6): Walters TR, Bushore M, Simone J: Poor prognosis in Negro children with acute lymphocytic leukemia. 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