Prognostic role of mismatch repair deficiency (MMR-D) in patients receiving first-line fluoropyrimidine and platinum (FP) doublet chemotherapy for metastatic and locally advanced unresectable gastric cancers (GCs).

Abstract

4566 Background: Although chemotherapy has been suggested to have the potential to cause a detrimental effect on treatment outcomes of localized GC with MMR-D, it remains unclear whether chemotherapy for metastatic/recurrent/unresectable GC with MMR-D would also adversely affect the survival outcomes. Anti PD-1 antibody (Ab) showed remarkable efficacy in patients with MMR-D and is being actively investigated in combination with cytotoxic chemotherapy. Hence, we aim to evaluate the impact of MMR status on treatment outcomes of advanced GC. Methods: We reviewed our database to identify all patients with HER2 negative, metastatic, recurrent, and locally advanced unresectable GC who received FP doublet chemotherapy from January 2015 to August 2018. For those who had an available tumor tissue, MMR protein expression was assessed by immunohistochemistry (IHC) and correlated with clinical characteristics and treatment outcomes. Results: Out of 895 patients identified from the database, 543 underwent IHC testing for MMR. The median age was 58 years (range, 24 – 86) with male comprising 64.0%. Most patients had initially metastatic disease (n = 382, 70.3%) followed by recurrent (n = 127, 23.3%) and locally advanced unresectable disease (n = 34, 6.3%). MMR-D was found in 4.4% (n = 24) and associated with age ≥ 65 years (50% vs. 29.9%; P = 0.04) and signet ring cell histology (0% vs. 17.7%, P = 0.01). According to our prognostic model (Koo DH et al, 2011), only 4.2% of patients with MMR-D were classified as Poor-risk group (vs. 16.8% of patients with MMR-P, p= 0.10). In the Good-risk group, patients with MMR-D (n = 10) had significantly shorter median progression-free survival (PFS, 6.0 vs. 9.0 months, P = 0.05) and overall survival (OS, 10.1 vs 20.9 months, P = 0.047) compared to those with MMR-P (n = 188), while there was no significant difference in survival outcomes depending on MMR status in the Moderate and Poor-risk groups. In multivariate analysis for OS, MMR status was a significant prognostic factor for OS in Good-risk group GC patients. Conclusions: GC patients with MMR-D had poorer median PFS and OS than those with MMR-P on standard cytotoxic chemotherapy in the Good-risk group. Thus, for Good-risk GC patients with MMR-D, anti PD-1 Ab alone might be considered rather than combining cytotoxic chemotherapy. Further investigation with next-generation sequencing is in process to determine underlying molecular mechanisms and will be presented in ASCO 2020.