Clinical and molecular characterisation of hereditary and sporadic metastatic colorectal cancers harbouring microsatellite instability/DNA mismatch repair deficiency

Publication date: November 2017
Source:European Journal of Cancer, Volume 86
Author(s): R. Cohen, O. Buhard, P. Cervera, E. Hain, S. Dumont, A. Bardier, J.-B. Bachet, J.-M. Gornet, D. Lopez-Trabada, S. Dumont, R. Kaci, P. Bertheau, F. Renaud, F. Bibeau, Y. Parc, D. Vernerey, A. Duval, M. Svrcek, Thierry André
BackgroundPatients treated with chemotherapy for microsatellite unstable (MSI) and/or mismatch repair deficient (dMMR) cancer metastatic colorectal cancer (mCRC) exhibit poor prognosis. We aimed to evaluate the relevance of distinguishing sporadic from Lynch syndrome (LS)-like mCRCs.Patients and methodsMSI/dMMR mCRC patients were retrospectively identified in six French hospitals. Tumour samples were screened for MSI, dMMR, RAS/RAF mutations and MLH1 methylation. Sporadic cases were molecularly defined as those displaying MLH1/PMS2 loss of expression with BRAFV600E and/or MLH1 hypermethylation and no MMR germline mutation.ResultsAmong 129 MSI/dMMR mCRC patients, 81 (63%) were LS-like and 48 (31%) had sporadic tumours; 22% of MLH1/PMS2-negative mCRCs would have been misclassified using an algorithm based on local medical records (age, Amsterdam II criteria, BRAF and MMR statuses when locally tested), compared to a systematical assessment of MMR, BRAF and MLH1 methylation statuses. In univariate analysis, parameters associated with better overall survival were age (P < 0.0001), metastatic resection (P = 0.001) and LS-like mCRC (P = 0.01), but not BRAFV600E. In multivariate analysis, age (hazard ratio (HR) = 3.19, P = 0.01) and metastatic resection (HR = 4.2, P = 0.001) were associated with overall survival, but not LS. LS-like patients were associated with more frequent liver involvement, metastatic resection and better disease-free survival after metastasectomy (HR = 0.28, P = 0.01). Median progression-free survival of first-line chemotherapy was similar between the two groups (4.2 and 4.2 months; P = 0.44).ConclusionsLS-like and sporadic MSI/dMMR mCRCs display distinct natural histories. MMR, BRAF mutation and MLH1 methylation testing should be mandatory to differentiate LS-like and sporadic MSI/dMMR mCRC, to determine in particular whether immune checkpoint inhibitors efficacy differs in these two populations.



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