Genetic Polymorphisms In Genes Involved In R-CHOP Metabolism and Event-Free and Overall Survival In Diffuse Large B-Cell Lymphoma

Treatment with R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone) has improved survival in diffuse large B-cell lymphoma (DLBCL) lymphoma, although a significant percentage of patients do not achieve a remission or they relapse. One potential explanation for this observation is that host pharmacogenetic background may impact metabolism, detoxification and transport of R-CHOP. However, there are few prospectively collected data that address pharmacogenetics in DLBCL, particularly for event-free and overall survival in the rituximab era. We therefore tested the hypothesis that functional candidate single nucleotide polymorphisms (SNPs) from genes involved in the metabolism of CHOP (CYP2C19, CYP3A5, ABCB1, ABCC2, ABCG2, RAC2, CYBA, NR3C1, GSTA1, GSTP1, TP53) and rituximab (FCGR2A, FCGR3A) influence prognosis in DLBCL.

We genotyped 19 SNPs from 13 genes in a prospective cohort of newly diagnosed DLBCL patients with germline DNA enrolled at the Mayo Clinic and University of Iowa from 2002–2008 as part of the Molecular Epidemiology Resource of the Iowa/Mayo Lymphoma SPORE. All patients were systematically followed through 2009 for overall survival (OS) and event-free survival (EFS), defined as disease progression, retreatment or death due to any cause. All SNPs were genotyped on the Illumina Golden-Gate platform. Cox regression was used to estimate Hazard Ratios (HRs) and 95% confidence intervals (CI) for individual SNPs with OS and EFS. Each SNP was modeled with the most prevalent homozygous genotype used as the reference group. An ordinal test was used to assess the trend across genotypes, and a p<0.05 was considered statistically significant. All Cox models adjusted for International Prognostic Index (IPI) and treatment.

The median age at diagnosis of the 439 DLBCL patients was 62 years (range 18–92). The IPI was distributed as follows: 0–1 (34%), 2 (26%), 3 (24%) and 4–5 (16%). All patients were treated with chemotherapy, and 91% received R-CHOP. Through 2009, there were 171 events (39%) and 122 (28%) deaths, with a median follow-up for living patients of 49 months (range 1–98). The SNP rs1045642 in the ATP-binding cassette (ABC) protein gene ABCB1 was associated with OS (p=0.012). The variant T allele for ABCB1 rs1045642 (minor allele frequency (MAF)=0.47) is associated with a silent I→I substitution, and the T allele predicts low enzyme expression. Compared to CC homozygotes, patients with CT (HR=0.66, 95% CI 0.44–0.99) or TT (HR=0.53, 95% CI 0.31–0.90) genotypes had superior OS. We also observed an association of the GSTP1 SNP rs1695 with OS (p-trend=0.018). The variant G allele (MAF of 0.31) is associated with an A→V substitution, and this change predicts low enzyme expression. Compared to AA homozygotes, patients with the AG (HR=0.78, 95% CI 0.54–1.14) or GG (HR=0.39, 95% CI 0.17–0.90) genotypes had superior OS. Nearly identical associations for these two SNPS were observed with EFS. There were no significant associations with any of the other SNPs that we evaluated.

In a large series of newly diagnosed DLBCL patients treated in the rituximab era, we found evidence that genetic variation in ABCB1 and GSTP1 is associated with improved OS and EFS after adjusting for IPI and treatment. The variant allele for ABCB1 is associated with slower enzyme activity, favorably impacting doxorubicin and vincristine pharmacodynamics, and the variant allele for GSTP1 is associated with slower detoxification of doxorubicin and vincristine, increasing bioavailability of these drugs. A comprehensive evaluation of the role of pharmacogenetics in DLBCL is warranted.

P50 CA97274, R01 CA129539.

No relevant conflicts of interest to declare.