TP53 Arg72 as a favorable prognostic factor for Chinese diffuse large B-cell lymphoma patients treated with CHOP

The clinical research protocol was approved by the Institutional Review Board and the Ethical Committee of Peking University School of Oncology, Beijing, China. All patients participating in this study signed the informed consent.

Four hundred and twenty-five patients with DLBCL confirmed by our Department of Pathology according to the World Health Organization classification were included in this study. Of the patients, 289 received rituximab in combination with a chemotherapy regimen between January 2000 and January 2015 at the Beijing Cancer Hospital, Peking University School of Oncology. Another 136 patients received CHOP or CHOP-like therapy (e.g. COP, CCOP, CHO or CHOPE) as the frontline chemotherapy. Based on the expression levels of Bcl-6, CD10, and MUM-1 measured by immunohistochemistry, cases were subdivided into germinal center B-cell (GCB) and non-GCB types according to the Hans algorithm [24, 25]. The response to chemotherapy was evaluated after completion of 2 to 3 courses of therapy and 1 to 2 months after completion of all treatment plans, then every 3 months for the first year and every 6 months thereafter until progression.

Overall survival (OS) was calculated from the date of disease confirmation to the date of last follow-up or death. Progression free survival (PFS) was identified as the period between the disease confirmation and progression (relapse and refractory) or disease-related death. Disease status was evaluated via clinical findings and computed tomography and classified as complete response (CR), unconfirmed complete response (CRu), partial response (PR), stable disease (SD), progressive disease or relapse according to the revised response criteria for malignant lymphoma [26, 27]. Patients who had heterozygous (GC) or homozygous G (GG) genotype of TP53 SNP rs1042522 were designated as G carriers.

Genomic DNA was extracted from whole blood using the Whole Blood Genome DNA isolation Kit according to the manufacturer’s instructions (Qiagen, Nussloch, Germany). DNA was diluted in AE buffer to a final stock concentration of 20 ng/μl, and 2 μl was used in each PCR reaction.

The general characteristics of the 425 DLBCL patients (175 male and 250 female) in this study are summarized in Table 1. The median age at diagnosis was 54 years (range, 15–90 years). Two hundred and forty-three (57.2%) patients were in stage 3 or 4, and 136 (32.0%) patients had intermediate-to-high or high international prognostic index (IPI) scores. One hundred and twelve (26.4%) patients were classified into GCB subgroup, 251 (59.1%) patients were classified into non-GCB subgroup, and 62 patients had incomplete records. Two hundred and thirty-four (55.1%) patients exhibited B symptoms at diagnosis and 109 (28.2%) patients showed an elevated β₂-MG level. Two hundred and eighty-nine (68%) patients were treated with R-CHOP therapy and 136 patients were treated with CHOP or CHOP-like therapy only.

We detected the genotype of TP53 SNP rs1042522 in 425 patients. As shown in Table 2, 28% patients carried the homozygous GG genotype (Arg/Arg), 53.2% patients had the heterozygous GC genotype (Arg/Pro), and18.8% patients carried the homozygous CC genotype (Pro/Pro). The frequency of the G allele in 425 patients was 55%, and the frequency of the C allele was 45%. The genotype distribution of SNP rs1042522 in the DLBCL population analyzed in this study was in Hardy-Weinberg equilibrium (P = 0.135), and the allele distribution was close to the frequency distribution seen in the Asian population based on the dbSNP database.

As shown in Table 1, patients with genotype GG and GC of SNP rs1042522 had a lower positive rate for β₂-MG than those with genotype CC (25.1% vs. 42.3%, P = 0.004). Although the G allele carriers showed a higher positive rate for B symptoms (58.1% vs. 42.5%, P = 0.012), the univariate analysis revealed that B symptoms is not an independent prognostic factor for overall survival (P = 0.983). The genotype distribution in CHOP or CHOP-like and R-CHOP treated subgroups is unbiased.

Of the 396 patients evaluable for response to CHOP or CHOP-like therapy with or without rituximab, the OR rate was 84.1% (333 of 396 patients), including a CR rate of 57.8% (229 of 396 patients) and a PR rate of 26.3% (104 of 396 patients). As shown in Table 3, of the 396 patients, patients with genotypes GG and GC exhibited higher CR and OR rates than those with the genotype CC (61% vs. 44%, P = 0.007; 86% vs. 76%, P = 0.033). The combination of rituximab in treatment significantly increased the CR rate (65% vs. 38%, P < 0.001). In the subgroup treated without rituximab, a relatively higher CR rate was achieved in patients with genotype GG and GC than in those with genotype CC (45.78% vs. 12.5%; P = 0.004). However, this significant difference vanished in the subgroup treated with combination of rituximab. In the subgroup treated with R-CHOP or R-CHOP-like, patients with genotypes GG and GC exhibited similar CR (66.4% vs. 58.8%, P = 0.304) rates and OR (87% vs. 76.5%, P = 0.056) rates to those with the CC genotype.

All 425 patients were evaluated for OS and PFS. After a median follow-up time of 56.23 months (range, 0.83–183.23 months), two hundred and fifty (58.8%) patients relapsed or progressed, 135 (31.8%) patients died and 40 (9.4%) patients lost follow-up. Patients with genotypes GG and GC had a median OS of 57.6 months and a median PFS of 49.7 month respectively, while patients with the genotype CC showed a median OS of 39.9 months and a median PFS of 18.1 months. In the subgroup treated with CHOP or CHOP-like therapy (Fig. 1), patients with genotype GG and GC had higher 5-year OS and PFS rates than those with genotype CC (68.8% vs. 23.2%, P = 0.001; 56.1% vs. 25.4%, P = 0.002, respectively). However, the integration of rituximab in treatment significantly increased the 5-year OS and PFS rates (57.1% vs. 72.8%, P = 0.001; 49.4% vs. 61.3%, P = 0.017) in the overall population. Therefore, in the subgroup treated with R-CHOP therapy (Fig. 2), the 5-year OS and PFS rates of CC patients are only about 10% lower than those of G allele carriers (63.0% vs. 74.9%, P = 0.218; 51% vs. 63.5%, P = 0.05) and did not reach the statistical significance.

Multivariate analyses were done to evaluate the following variables on OS: age (≤60 vs. >60 years), stage (stages I-II vs. III-IV), IPI score (0–2 vs. 3–5), subtype (GCB vs. Non-GCB), β₂-MG (positive vs. negative), LDH (positive vs. negative), ESR (positive vs. negative), ECOG score (0–2 vs. 3–4), treatment (CHOP/CHOP-like vs. R-CHOP), and the genotype of TP53 SNP rs1042522 (GG + GC vs. CC). As shown in Table 4, along with known baseline predictors, treatment with rituximab was confirmed as a favorable prognostic factor (P < 0.001, HR = 0.377, 95% CI = 0.222–0.521). Interestingly, focusing only on patients treated without rituximab (Table 5), multivariate analysis revealed the G allele of TP53 SNP rs1042522 (TP53 Arg72) as a favorable prognostic factor (P = 0.002, HR = 0.343, 95% CI = 0.173–0.679).