CLL in India May Have a Different Biology from That in the West

Chronic lymphocytic leukaemia (CLL) is reported to be an uncommon hematopoietic malignancy in the Indian subcontinent (1.7-8.8%), whereas it is seen in 25-30% of all leukemias in west. Previous reports from India report CLL to occur at younger age, have larger spleen and present in high risk Rai stages. It is possible that this more aggressive disease in India may be due to differences in the biology of CLL in India. Thus, in the present study we aimed to elucidate the prevalence of various known biological and molecular prognostic parameters in CLL patients in India to evaluate the biology of CLL in India.

100 newly diagnosed cases of CLL along with 50 healthy individuals in similar age group, were taken for the study. Flowcytometry was performed for ZAP70 and CD38. Molecular studies were performed to include mutational analysis of IGVH and P53 gene, and PCR RFLP for polymorphism of P2X7 (1513 A-C) and BaxG (-248) A gene. Sandwich ELISA was performed to determine level of serum beta 2 microglobulin and Thymidine kinase. FISH cytogenetics was available in 30 patients. Patients with asymptomatic early stage disease (Rai 0) were monitored without therapy unless they had evidence of disease progression. Patients with intermediate (Rai stage I and II) and high (Rai stage III and IV) risk were treated conventionally with Fludarabine+ Cyclophosphamide + Rituximab (FCR) or Bendamustin+ Rituximab (BR).Response to induction chemotherapy was assessed according to the criteria proposed by the National Cancer Institute (NCI) sponsored Working Group Guidelines for CLL. Outcome analysis was based on Progression free survival (PFS), Treatment free survival (TFS) and Overall survival (OS).

Median age of CLL patients at presentation was 60.5 years (range 35 - 82); M:F:: 3.7:1 and haemoglobin 11.3 g/dl (range 4.6 - 15.3g/dl); Rai stage 0 was seen in 26% patients, Rai stage I in 15%, Rai stage II in 28%, Rai stage III in 16% and Rai stage IV in 15% patients. Diffuse involvement of bone marrow biopsy by CLL was seen in 65% patients. Treatment was given to 78% patients during the study period. Response to chemotherapy was observed in 48/78 (61.5%) with complete response (CR) in 19 (24.3%) patients and partial response (PR) in 29(37.2%) patients, while 30/78 (38.5%) patients showed no response. The median follow-up of the study group was 36.11 months (range 1.03 to 71.7 months).

High risk cytogenetic abnormalities like 17p- and 11q- were seen in 13.3 % patients .This is thus more common in India than that reported in the West. Expression of Zap70 only was seen in 37% patients, CD38 only expression in 44% of patients and combined expression of Zap70 and CD38 expression was present in 26%.Unmutated IGVH genes were seen in 36% patients, a prevalence similar to that in the West.The highest prevalence was of VH1-69 gene segment (10%) followed by VH3-73; (7%), VH3-48; (6%), VH2-70; (5%), VH3-23; (4%) and VH1-03; (3%). 8/10 of VH1-69 IGVH gene were unmutated and 5/8 patients died. Gene segments VH3-23 and VH3-21, each of which is known to be a bad prognostic marker, were found in 4 and 2 % each. However, VH3-73, VH3-48, and VH2-70 gene segments, which were found to be associated with poor prognosis in our study, showed a higher prevalence in Indians, compared to West. TP53 mutation ,examined in highly conserved region between Exon-5 and Exon-9,was seen in 18/100 (18%) patients,5/18 mutations were seen in Exon-6 and Exon-8. 2 mutations was present each in Exon-7 and Exon-9, and four patients showed mutation in Exon-5. Analysis of P2X7 (1513A-C) gene polymorphism revealed 33/100 (33%) patients to have heterozygous genotype (1513A/C) and 13/100 (13%) patients to have homozygous genotype (1513C/C), while Bax G(-248)A gene polymorphism showed the frequency of GG, GA, and AA genotypes were 78%, 18%, and 4% respectively. P2X7 and Bax gene polymorphism had no prognostic significance. Serum β2-microglobulin level (≥ 4.5 ug/ml) was seen in 36% patients and Thymidine kinase level (≥7.4 U/L) was seen in44% patients.

The above results indicate that ,in contrast to reported prevalence from the West, Indian CLL has higher prevalence of bad prognostic markers like CD38 expression, combined Zap70 and CD38expression, 17p-, 11q-, TP53 mutation, β2-microglobulin level and VH3-73, VH3-48, and VH2-70 gene segments of IGVH which may be responsible for a different biology.