642 Background: HER2 amplifications have been observed in approximately 3% of patients (pts) with metastatic colorectal cancer (mCRC). Early clinical trials with combined HER2-targeted therapies showed promising activities. However, it remains unclear whether HER2 amplification in mCRC is as prognostic as RAS or BRAF V600E mutant (mt). We aimed to evaluate survival outcome for mCRC pts with HER2 amplification compared to those with RAS or BRAF mt. Methods: mCRC pts who received a palliative resection of the primary tumor with metastatic diseases at presentation, or recurred after curative resection of the primary tumor between 2005 and 2015, were analyzed. HER2 immunohistochemistry (IHC) was performed using formalin-fixed and paraffin-embedded (FFPE) sections obtained from the primary tumor, and HER2 amplification was confirmed by fluorescence in situ hybridization (FISH) in case of IHC 2+ or 3+. Criteria for HER2 amplification were a HER2- to CEP17- signal ratio of 2.0 or higher. RAS / BRAF status was centrally assessed by a PCR-based method. The pts were classified into four subgroups based on RAS, BRAF and HER2 status: Group R , RAS mt; Group B, BRAF V600E mt; Group H, HER2 amplification with RAS / BRAF wild-type (wt); and Group W, RAS / BRAF wt. Results: Among 370 pts, 359 pts (97%) were successfully analyzed. A total of 15 pts (4%) had HER2 amplifications, out of which four pts had overlapped RAS mt (subclassified as Group R). RAS or BRAF mutations are mutually exclusive. The number in Group R, B, H and W was 204 (57%), 13 (4%), 11 (3%) and 131 (36%), respectively. There was no remarkable difference in baseline characteristics among groups. With a median follow-up time of 63 months (mos), the median overall survival of the 359 pts was 27 mos (95%CI 24 - 29 mos); Group R, 24 mos; Group B, 14 mos; Group H, 20 mos; and Group W, 39 mos. The HR of R vs. H is 0.83 (95%CI 0.41-1.70, p= 0.618), B vs. H is 1.16 (95%CI 0.47-2.84, p= 0.748), and W vs. H is 0.52 (95%CI 0.25-1.08, p= 0.080), respectively. Conclusions: This study suggests that the prognosis of mCRC pts with HER2 amplification tends to be worse as compared to those with RAS / BRAF wt, similar to those with RAS mt, and better than those with BRAF mt, although these comparisons were not statistical significant.
Association between HER2 amplification and cetuximab efficacy in patients with RAS wild-type metastatic colorectal cancer
