Influence of Molecular Status on Recurrence Site in Patients Treated for a Stage III Colon Cancer: a Post Hoc Analysis of the PETACC-8 Trial

BACKGROUND: Recurrence patterns in stage III colon cancer (CC) patients according to molecular markers remain unclear. The objective of the study was to assess recurrence patterns according to microsatellite instability (MSI), RAS and BRAFV600E status in stage III CC patients. METHODS: All stage III CC patients from the PETACC-8 randomized trial tested for MSI, RAS and BRAFV600E status were included. The site and characteristics of recurrence were analyzed according to molecular status. Survival after recurrence (SAR) was analyzed. RESULTS: A total of 1650 patients were included. Recurrence occurred in 434 patients (26.3%). Microsatellite stable (MSS) patients had a significantly higher recurrence rate (27.2% vs. 18.7%, P = 0.02) with a trend to more pulmonary recurrence (28.8% vs. 12.9%, P = 0.06) when compared to MSI patients. MSI patients experienced more regional lymph nodes compared to MSS (12.9% vs. 4%, P = 0.046). In the MSS population, the recurrence rate was significantly higher in RAS (32.2%) or BRAF (32.3%) patients when compared to double wild-type patients (19.9%) (p < 0.001); no preferential site of recurrence was observed according to RAS and BRAFV600E mutations. Finally, decreased SAR was observed in the case of peritoneal recurrence or more than two recurrence sites. CONCLUSIONS: Microsatellite, RAS and BRAFV600E status influences recurrence rates in stage III CC patients. However, only microsatellite status seems to be associated with specific recurrence patterns. More than two recurrence sites and recurrence in the peritoneum were associated with poorer SAR.