Cytogenetic Profile in Pediatric Acute Lymphoblastic Leukemia and Impact On Survival: Single Centre Experience From India.

Biological subtypes of pediatric Acute Lymphoblastic Leukemia (ALL) have emerged as the most important prognostic factor for response to treatment. Since the genetic subtypes differ according to ethnic groups, it becomes important to consider this factor while comparing survival between different geographic areas. We describe the relative frequency of genetic subtypes and the effect on survival and duration of first remission in patients diagnosed with ALL from a single centre in India.

Bone marrow karyotyping and fluorescent in-situ hybridization (FISH) studies for BCR ABL and TEL AML1 were performed on 98 children diagnosed with ALL at Sir Ganga Ram Hospital, Delhi between Jan 2005 and June 2009. During this period of 54 months, a total of 176 patients were diagnosed with ALL. Cytogenetic analysis could be done only in 98 patients. It could not be done in others due to monetary constraints. 27 did not have adequate metaphase for karyotyping. In those patients with normal karyotype but positive FISH for BCR ABL, quantitative polymerase chain reaction (Q PCR) was done. Those who were positive either by Q-PCR for BCR ABL or by karyotype for t (9; 22) were considered as Philadelphia (Ph) positive for treatment and survival analysis. The treatment protocol used was UK ALL XI for standard risk and BFM 95 for high risk ALL. Ph positive cases were managed with Imatinib mesylate along with chemotherapy. 16 patients were lost to follow up (LFU) and excluded from survival analysis.

The median age of our study population was 4 years (0.5-18 years). Male: female ratio was 2:1. Most patients had Pre B CALLA positive ALL (n=90). There were 3 cases CALLA negative ALL, 3 of T cell ALL and 2 of biphenotypic leukemia. T cell ALL was 3% in the study population as compared to 10% in all children diagnosed at our centre. Among 71 cases in which karyotype was analyzed, 15 (21.1%) patients had hyperdiploidy, 5 (7 %) had t (9; 22) and 9 (12.7%) had structural abnormalities. TEL AML1 was detected by FISH in 6 (9.4%) out of 64 patients of Pre B ALL. FISH for BCR ABL was positive in 10 (14%) patients, 8 of which were negative for BCR ABL fusion by Q PCR and were considered as false positive. Thus true Ph positive cases were 7 (8.5%) out of 82 cases (5 karyotype, 2 Q PCR). With a median follow up duration of 22 months, the estimated overall survival (OS) and event free survival (EFS) at 30 months were 70.5 ± 6.5% and 60 ± 7.4% respectively. The mean duration of first clinical remission (CR) was 19 ± 2 months. Hyperdiploidy was more common in girls (30.4%) compared to boys (14.6%, p=0.11). It was not significantly associated with any age group or WBC count at presentation. The EFS and OS were not found to be significantly different from the group without hyperdiploidy. The mean CR duration was 8.7 months, probably because 3 cases were diagnosed 2 months prior to the end of the study period. 2 patients with hyperdiploidy died in induction and one died following a road traffic accident. One child developed intestinal mucormycosis with perforation and hence suffered a break in treatment. This child had a CNS relapse 13 months later. TEL AML1 fusion was also more common in girls (18.2%) compared to boys (4.8%), (p=0.17). All positive cases were between 2-9 years of age and all had initial WBC count <50,000/mL. The mean CR duration was 15.1 months. The estimated OS and EFS, excluding case 1 LFU, was 100% at 30 months. Among the Philadelphia positive cases, there was no significance noted in age, sex or initial WBC counts. The mean CR duration was 19.9 months. There was no difference in OS or EFS noted in this group compared to patients with normal cytogenetics. 1 patient relapsed and refused further treatment. Another patient underwent matched sibling donor stem cell transplant in first CR but developed grade IV GVHD and died.

Earlier reports from India have suggested a larger prevalence of high risk factors like T cell disease and lesser prevalence of favorable factor like TEL AML1. T cell disease is under-represented in this report, as most of these patients could not afford these investigations. False positivity of bcr-abl on FISH study was frequent. We recommend confirmation by QPCR. The survival of Ph positive cases was not worse probably because of inclusion of Imatinib mesylate in the treatment regimen. Overall, good prognostic factors such as TEL AML1 and hyperdiploidy were less commonly seen in our population than in the West.

No relevant conflicts of interest to declare.