3525 Background: Microsatellite instable/deficient mismatch repair (MSI) metastatic colorectal cancers have been reported to be of poor prognosis. The interaction between MSI and BRAFV600E mutation complicates the picture. Methods: Patients with resected stage III CC from 7 studies with disease recurrence and data available for MSI and BRAFV600E status were analyzed. The primary endpoint was survival after recurrence (SAR) to assess the prognostic roles of MSI and BRAFV600E, respectively. Associations of markers with SAR were analyzed using Cox proportional hazards models adjusted for clinicopathologic features (data collected 12/1998 to 11/2009). Results: Among 2630 patients with cancer recurrence (1491 men [56.7%], mean age, 58.5 [19-85] years), multivariable analysis revealed that patients with MSI tumors (n = 220) had significantly better SAR (adjusted hazard ratio [aHR], 0.82; 95% CI, 0.69-0.98; P = .029) than patients with microsatellite stable /proficient MMR (MSS) tumors (n = 1766). This was also observed when looking at patients treated by the standard FOLFOX adjuvant regimen only (aHR, 0.76; 0.58-1.00; P = .048). Same trends were observed when looking at MSI/dMMR patients outcome in BRAFV600E wild-type (aHR, 0.84; P = .10) and mutant (aHR, 0.88; P = .43) subgroups separately, without reaching statistical significance. As previously described poor SAR was observed in BRAFV600E mutants vs wild type patients (n = 244; aHR, 2.06; 95% CI, 1.73-2.46; P < .0001) and this was also true in BRAFV600E mutants MSI/dMMR patients (n = 77, aHR, 2.65 ; 95% CI, 1.67-4.21; p < .0001). Other factors associated with a poor SAR were : olderage, male gender, T4/N2, proximal primary tumor location, poorly differentiated adenocarcinoma, and early recurrence (by 1y increase). Conclusions: In stage III colon cancer patients recurring after adjuvant chemotherapy and before the era of immuno-oncologic agents, MSI/dMMR was associated with a better survival compared to MSS. BRAFV600E mutation seems to be a poor prognostic factor for both MSI/dMMR and MSS/pMMR patients.
Adjuvant FOLFOX+ cetuximab vs FOLFOX in full RAS and BRAF wild type stage III colon cancer patients: Results from the PETACC8 trial