Abstract
Abstract 442
Scant information is availabel on the impact of the host genetic background in predicting outcome of diffuse large B cell lymphoma (DLBCL). We recently documented that host single nucleotide polymorphisms (SNPs) affecting doxorubicin pharmacodynamics and alkylator detoxification may predict outcome in R-CHOP-treated DLBCL (Rossi et al, Leukemia 2009; 23:118-26). Several DNA repair mechanisms are involved in resistance to R-CHOP drugs. We verified whether SNPs of DNA repair genes may further refine prognostic stratification and toxicity prediction in DLBCL treated with R-CHOP. The study was based on 163 consecutive DLBCL treated with R-CHOP and provided with a prospectively collected dataset. At diagnosis, age >60 years was observed in 104/163 (63.8%) cases, ECOG PS >1 in 21/163 (12.9%), extranodal sites >1 in 41/163 (25.2%), Ann Arbor stage III-IV in 85/163 (52.1%), bulky disease in 46/163 (28.2%), B symptoms in 38/163 (23.3%), LDH elevation in 75/163 (46.0%), IPI >2 in 55/163 (33.7%). Median follow up was 40 months. Candidate SNPs selected for the analysis belonged to genes involved in repairing DNA damage produced by R-CHOP drugs, and included SNPs affecting the following DNA repair mechanisms: i) base excision repair (OGG1 rs1052133); ii) nucleotide excision repair (ERCC2 rs1799793, ERCC2 rs13181, ERCC6 rs3793784, ERCC6 rs2228528, ERCC6 rs2228529, XPA rs1800975, XPC rs2227999, XPC rs2228000); iii) mismatch repair (MLH1 rs1799977); iv) double strand break repair (LIG4 rs1805388, XRCC6 rs132788, XRCC6 rs55751129, BRCA1 rs799917). Genotyping was performed by SNP-minisequencing on DNA extracted from granulocytes. Clinical endpoints considered in the study were overall survival (OS), progression free survival (PFS) and toxicity. Associations of SNPs with clinical endpoints were controlled for multiple testing by FDR analysis. Among the SNPs included in the study, univariate log-rank analysis controlled for multiple comparisons by FDR testing identified MLH1 rs1799977 as a predictor of both PFS and OS in DLBCL treated with R-CHOP. MLH1 encodes a DNA mismatch repair gene involved in alkylating agents and doxorubicin resistance. DLBCL patients carrying the MLH1 rs1799977 AG/GG genotypes displayed a poorer PFS (Events/N: 23/52; 3-year PFS: 51.9%) compared to DLBCL patients carrying the MLH1 rs1799977 AA genotype (Events/N: 33/111; 3-year PFS: 72.0%) (p=.020; q=.240) (Fig. 1). Other variables predicting PFS were ECOG PS (p=.042), Ann Arbor stage (p=.035), bulky disease (p=.001), number of extranodal sites (p=.009), LDH (p=.007), and IPI (p=.002). Multivariate analysis selected MLH1 rs1799977 AG/GG (HR: 1.17; p=.034) as an independent predictor of PFS, along with IPI (HR: 1.44; p=.002) and bulky disease (HR: 2.20, p=.004). The MLH1 rs1799977 genotype was also relevant for predicting DLBCL survival, since DLBCL patients carrying the MLH1 rs1799977 AG/GG genotypes displayed a poorer OS (Events/N: 19/52; 3-year OS: 61.8%) compared to DLBCL patients carrying the MLH1 rs1799977 AA genotype (Events/N: 18/111; 3-year OS: 83.3%) (p=.001; q=.013) (Fig. 2). Other variables predicting OS were age (p=.026), ECOG PS (p=.002), bulky disease (p<.001), number of extranodal sites (p=.027), IPI (p=.020), relative dose intensity of doxorubicin (p=.017), and comorbidity score (p=.003). Multivariate analysis selected MLH1 rs1799977 AG/GG (HR: 2.84; p=.002) as an independent predictor of OS, along with IPI (HR: 1.40; p=.013) and bulky disease (HR: 3.20; p=.001). The impact of SNPs was also evaluated for toxicity in 803 R-CHOP courses. A multivariate model for toxicity was built by generalized estimating equations (GEE), which adjust for the clustering of treatment courses within a patient. After correcting for multiple comparisons and adjusting for potentially confounding variables, none of the DNA repair SNPs analysed was found to be associated with R-CHOP toxicity. Overall, MLH1 rs1799977 SNP is an independent predictor of progression and survival in DLBCL treated with R-CHOP. The biologic plausibility of this association is supported by two lines evidence: i) MLH1 rs1799977 G variant allele is known to reduce MLH1 protein expression and function; ii) loss of MLH1 DNA mismatch repair function is known to result in in vitro resistance to doxorubicin and alkylating agents. Consistently, DLBCL carriers of the MLH1 rs1799977 AG/GG genotypes displayed poor PFS and OS possibly due to altered MLH1 function.
No relevant conflicts of interest to declare.
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