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Twenty-one acute myelogenous leukemia (AML) patients were submitted in second remission (II CR) to BAVC conditioning regimen followed by unpurged ABMT. Transplant was done after a median of 2 months from II CR (range, 1 to 13). Median first remission (I CR) duration was 16 months (range, 1–35). Conditioning regimen was well tolerated, with no major extra-medullary toxicity. One patient died during aplasia from fungal sepsis. Of the 20 evaluable patients, nine relapsed after a median time of 6 months (range, 2 to 18). Eleven patients are in continuous complete remission (CCR) after a median follow-up of 40 months (range, 24 to 63). The duration of II CR has exceeded the duration of I CR in all patients in CCR. Projected probability of disease-free survival is 52% at 63 months.

Hybrid fusion genes are specific tumor markers of several leukemic subtypes. The use of reverse transcription-polymerase chain reaction (RT-PCR) to amplify chimeric cDNAs allows sensitive detection of the neoplastic clone for diagnostic and monitoring studies in these leukemias. Nonetheless, the clinical relevance of minimal residual disease (MRD) evaluation by PCR remains controversial. In this study, 9 patients (pts) with acute promyelocytic leukemia (APL) in long-term remission for 4 to 12 years were analyzed for the presence of MRD by RT- PCR amplification of the specific PML/RAR-alpha fusion gene. Seven pts had been treated with conventional chemotherapy (CHT) alone, 1 had undergone allogeneic bone marrow transplantation (BMT), and 1 autologous BMT as consolidation therapy after CHT. In 8 cases, the presence of the t(15;17) rearrangement could be documented in diagnostic BM specimens by cytogenetic and/or molecular analysis. A two- rounds “nested” RT-PCR assay with sensitivity levels of 1 in 10(5) was used to analyze BM samples collected at 32 to 141 months from the achievement of complete remission (CR). In no cases were residual PML/RAR-alpha transcripts detectable in these remission controls. All patients are in unmaintained CR at 48 to 154 months from CR and at 6 to 17 months from PCR evaluation. These results suggest that long-term survival of APL is associated with eradication of cells carrying the specific PML/RAR-alpha rearrangement, indicating that PCR negativity should be considered the therapeutic goal in these patients. Our findings further strengthen the clinical relevance of PCR monitoring studies in APL, as opposite to other leukemic subtypes (chronic myeloid leukemia and acute myeloid leukemia-M2) in which the prognostic significance of PCR evaluation is unclear.

Seventy patients with acute promyelocytic leukemia (APL) were characterized at the DNA level using genomic retinoic acid receptor- alpha (RAR-alpha) probes on Southern blot experiments. Sixty-two cases were defined as M3 according to the French-American-British (FAB) criteria, and eight had a diagnosis of microgranular or variant (M3v) APL. The use of two restriction enzymes and three probes exploring the second intron of the RAR-alpha gene allowed us to detect specific abnormal DNA fragments in every case, with clustering of rearrangements within the 20-kb intronic region between RAR-alpha exons II and III. A more detailed mapping of APL breakpoints was performed in 52 cases in which three EcoRI subregions of the RAR-alpha second intron were analyzed with corresponding probes. Comparison of clinical and hematological features in the three subgroups of patients with distinct RAR-alpha breakpoints did not show significant differences regarding age, peripheral blood (PB) counts, presence of coagulopathy, or FAB classification (M3 v M3v). Interestingly, a significant difference was observed in the M/F ratio of the three subgroups, with a higher incidence of rearrangements at the 5' end of the RAR-alpha second intron in female patients, and more frequent 3' breakpoints in males. The results of this study indicate that a unique genomic alteration consistently occurs on the 17q- derivative of the APL specific t(15;17) aberration. Moreover, the clinical relevance of RAR-alpha gene analysis both at diagnosis and in follow-up studies is further emphasized.

From March 1993 to October 1993, 20 consecutive, newly diagnosed acute promyelocytic leukemia (APL) patients from 13 Italian institutions entered in a pilot study named AIDA, combining all-trans retinoic acid (ATRA) with idarubicin (IDA). ATRA was administered orally beginning on the first day of induction at the dosage of 45 mg/m2/d until complete remission (CR), whereas IDA was administered intravenously at the dosage of 12 mg/m2/d on days 2, 4, 6, and 8 of the induction. Patients who achieved CR were consolidated with 3 courses of chemotherapy without ATRA; thereafter, they were followed up for molecular and hematologic CR. The median age was 35.3 years (range, 6.5 to 67.6 years); 8 patients were males and 12 females; 4 had the hypogranular variant of APL (M3v), and 4 (2 with M3v) presented with leukocyte counts > or = 10,000/microL. Molecular analysis for the promyelocytic leukemia-retinoic acid receptor alpha (PML-RAR alpha) hybrid gene at diagnosis was performed in 16 patients by means of reverse transcription-polymerase chain reaction (RT-PCR) analysis, and all were RT-PCR+ for the hybrid gene. In the remaining 4 patients, the cytogenetic study showed the presence of the t(15;17). After a median time of 36 days (range, 28 to 52 days) 18 (90%) patients achieved CR; the remaining 2 patients died 12 and 34 days after diagnosis from myocardial infarction caused by fungal myocarditis and from massive hemoptysis, respectively. ATRA syndrome was observed in only 2 patients, and, after the prompt discontinuation of ATRA and initiation of dexamethasone, both recovered from the syndrome. However, after recovering, 1 patient achieved CR, whereas the other died at day 34 because of massive hemoptysis; other side effects were very limited. At recovery from the third consolidation course, only 3 of 14 (21.4%) tested patients were RT-PCR+ for the PML-RAR alpha hybrid gene. Of these, 2 relapsed shortly afterwards; however, in the last patient, the PML-RAR alpha disappeared at successive testing performed 2 months later. As of September 30, 1995, after a median follow-up period from diagnosis of 27 months (range, 24 to 31 months), the overall survival and event-free survival durations are 85% and 69%, respectively; moreover, 14 of 18 (78%) patients who achieved CR are still alive and in first molecular and hematologic CR. Of the 4 relapsed patients, 3 achieved a second CR with ATRA and, after further treatment, are now in molecular and hematologic CR after 4+, 16+, and 17+ months from the second CR. These results indicate that (1) the AIDA protocol is highly effective in treating APL; (2) after 3 consolidation courses, the majority of patients who achieved CR are RT-PCR- for the hybrid gene PML-RAR alpha; (3) the persistence of an RT-PCR positivity for the PML- RAR alpha hybrid gene after 3 consolidation courses is indicative of early relapse, thus these patients still require additional treatment. These results have prompted the Gruppo Italiano Malattie Ematologiche Maligne dell′Adulto (GIMEMA) to initiate, in cooperation with the Associazione Italiana di Ematologia ed Oncologia Pediatrica and some European Organization for Research and Treatment of Cancer (EORTC) centers, a new multicentric clinical trial named AIDA LAP 0493 for the treatment of adult and pediatric APL patients. All patients are considered eligible if APL diagnosis is confirmed with molecular or cytogenetic studies for PML-RAR alpha hybrid gene or t(15;17) and are enrolled to receive the same induction and consolidation therapy of this pilot study. After consolidation, patients who are RT-PCR- for PML- RAR alpha hybrid gene are randomized to four arms, whereas patients who are RT-PCR+ after consolidation undergo, if eligible, an allogenic transplantation procedure.

The advent of retinoic acid (RA) in the treatment of acute promyelocytic leukemia (APL) has led to a high frequency of short- lasting complete remissions (CR). We studied the response to RA by molecularly analyzing the RA receptor alpha (RAR alpha) locus, which has recently been shown to be rearranged in all APLs. Southern blot analysis demonstrated that the RAR alpha rearrangements persisted in the APL samples containing maturing myeloid cells 2 to 3 weeks after the start of RA treatment, but disappeared after 5 to 8 weeks, when the patients achieved CR. Our investigations provide clear evidence that CR occurs at molecular level and that there is reconstitution of an apparently normal, nonclonal hematopoiesis. Further, it shows that RA acts by triggering differentiation rather than by exerting a cytotoxic effect on the leukemic clone.