Correlation of histopathologic regression with progression free survival (PFS) in patients (pts) with RAS wildtype metastatic colorectal cancer (mCRC) under fluorouracil/folinic acid, irinotecan, and oxaliplatin (FOLFOXIRI) plus panitumumab (pmab) or FOLFOXIRI alone: Subgroup analysis of VOLFI (AIO-KRK-0109).

Abstract

e15024 Background: We recently demonstrated improved objective response rate in untreated all-RAS wildtype mCRC with the addition of the anti-EGFR-antibody pmab to FOLFOXIRI. In this subgroup analysis we focused on histopathological response as a predictive marker for PFS. Additionally we analyzed chemotherapy induced steatosis hepatitis (CASH) in both treatment arms. Methods: Tissue samples from pts. achieving secondary resection of liver metastases in VOLFI were analyzed. We defined a cut-off for very good histopathological response at 20% of residual tumor cells in proportion to the total tumor area. For CASH sinusoidal obstructive syndrome, ballooning, steatosis, cholestasis, fibrosis and inflammation were determined. PFS was estimated using LIFETEST procedure. Results: Tissue of 14/19 resected pts. was evaluable (pmab-FOLFOXIRI/FOLFOXIRI: 11/3). All showed partial remission by RECIST. Median age was 56 yrs. (32–67), male/female: 7/7. All primary tumors were located in the left colon. Molecular analysis detected 1 BRAF (V600E) mutation and 1 MSI-H tumor. Median treatment duration until resection in this cohort: pmab-FOLFOXIRI 7 cycles (3-12)/FOLFOXIRI 9.5 cycles (7-11).7 pts. achieved very good histopathological response with vital tumor cells ≤20% (pmab-FOLFOXIRI/FOLFOXIRI 5/2) and 7 pts. showed vital tumor cells >20% (pmab-FOLFOXIRI/FOLFOXIRI 6/1). The cut-off correlated with an improved PFS in the group ≤20 vs >20% (median PFS 12.40; confidence interval (CI) 6.43-51.22 vs PFS 9.88; CI 6.17-15.26 months). The severity of CASH was not increased by the addition of pmab. Conclusions: In this preliminary analysis of VOLFI histopathological response seems to correlate with a better PFS after secondary resection of liver metastases. There was no relevant difference in CASH between pmab-FOLFOXIRI vs. FOLFOXIRI alone. The trial is registered with ClinicalTrials.gov, NCT01328171. Clinical trial information: AIO-KRK-0109.