P-21 Molecular subtypes (profile) of colorectal cancer and their correlation with clinical and pathological profile in a tertiary care centre in India

Abstract

Colorectal cancer is a heterogeneous disease with 3 molecular carcinogenesis pathways and 2 morphologic multistep pathways. The varied response rates to the standard therapeutic regimens is due to its heterogeneous tumor biology. A lot of the literature is from the western world on this molecular heterogeneity. We aimed to study the molecular subtypes of colorectal cancer and the correlation with clinical and pathological characteristics in Indian population.Objectives: To evaluate the clinical and pathological profile of colorectal cancers, to determine the frequency of molecular subtypes of colorectal cancers, to correlate between the molecular subtypes and their clinic-pathological features and to determine the association between different molecular subtypes of colorectal cancer. It is a prospective non-invasive interventional study done in 50 patients (both outpatients and inpatients) with newly diagnosed colorectal cancers presenting to Rajiv Gandhi Cancer Institute and Research Centre, Rohini, Delhi from February 2019 to March 2020. Clinical and histopathological data was collected from case sheets as per study proforma- history and physical examination, non-invasive and invasive imaging and histopathological reports. Patients in whom tissue was insufficient or not available for testing for at least 3 molecular markers out of 5 (KRAS, NRAS, BRAF, MSI and MLH1methylation) were excluded. Molecular testing for MMR protein analysis was done using Immunohistochemistry (BenchMark XT, Ventana Medical Systems, Inc., Tucson, AZ, USA). Germline mutation analysis in MSH2, MLH1, PMS2 and MSH6 as dictated by the MMR protein analysis. KRAS, NRAS and BRAF V600E mutation analysis was done by RT-PCR. Methylation of CpG islands of MLH1 is done by pyrosequencing. Results were analyzed with SSPS 23.0 software. For comparison of the frequencies among groups, the Chi-square test and the Fisher exact test were used. P-value <0.05 was considered statistically significant. The median age was 53 years. Majority of males (54%) had CRC. 44% were right sided colon tumors. Of the 50 patients with CRC 40%, 4% and 22% had KRAS mutation, BRAF mutation and deficient MMR respectively. None of the patients was NRAS mutant. KRAS mutation was significantly associated with upfront liver metastases (p=0.02) and well/moderate differentiation (p =0.02). BRAF wild tumors were likely to be well-differentiated (p=0.02) and moreover, half of them (52%) had MLH1 promoter methylation. The proportion of dMMR was higher in male patients (p = 0.04). Deficient mismatch repair was associated with well/moderate differentiation (p = 0.02), early stage (p =0.02) and mild peri-tumoral lymphocytes (p=0.01). None of the MMR deficient patients had Stage IV CRC. 27% patients (3/11) with dMMR tumors had germline mutation of MMR genes. Majority of MMR deficient tumors (43%, 3 out of 7) had MLH1 promoter methylation. Overall, 45% (5/11) dMMR tumors harbored KRAS mutation. In conclusion, this prospective study evaluated the correlations between RAS/BRAF mutation and MMR status with clinico-pathological characteristics in Indian CRC patients, which is mostly similar to worldwide reports with some exceptions. It paves way for future studies to include large populations for validation of the molecular heterogeneity and their prognostic value in Indian population.