HER2 Gene Expression Levels Are Predictive and Prognostic in Patients With Metastatic Colorectal Cancer Enrolled in CALGB/SWOG 80405.

Purpose: The phase III Cancer and Leukemia Group B (CALGB)/SWOG 80405 trial found no difference in overall survival (OS) in patients with metastatic colorectal cancer receiving first-line chemotherapy in combination with either bevacizumab or cetuximab. We investigated the potential prognostic and predictive value of HER2 amplification and gene expression using next-generation sequencing (NGS) and NanoString data.
Patients and Methods: Primary tumor DNA from 559 patients was profiled for HER2 amplification by NGS (FoundationOne CDx). Tumor tissue from 925 patients was tested for NanoString gene expression using an 800-gene panel. OS and progression-free survival (PFS) were the time-to-event end points.
Results: High HER2 expression (dichotomized at median) was associated with longer PFS (11.6 v 10 months, P = .012) and OS (32 v 25.3 months, P = .033), independent of treatment. An OS benefit for cetuximab versus bevacizumab was observed in the high HER2 expression group ( P = .02), whereas a worse PFS for cetuximab was seen in the low-expression group ( P = .019). When modeled as a continuous variable, increased HER2 expression was associated with longer OS (hazard ratio [HR], 0.83 [95% CI, 0.75 to 0.93]; adjusted P = .0007) and PFS (HR, 0.82 [95% CI, 0.74 to 0.91]; adjusted P = .0002), reaching a plateau effect after the median. In patients with HER2 expression lower than median, treatment with cetuximab was associated with worse PFS (HR, 1.38 [95% CI, 1.12 to 1.71]; adjusted P = .0027) and OS (HR, 1.28 [95% CI, 1.02 to 1.59]; adjusted P = .03) compared with that with bevacizumab. A significant interaction between HER2 expression and the treatment arm was observed for OS ( P _intx = .017), PFS ( P _intx = .048), and objective response rate ( P _intx = .001).
Conclusion: HER2 gene expression was prognostic and predictive in CALGB/SWOG 80405. HER2 tumor expression may inform treatment selection for patients with low HER2 favoring bevacizumab- versus cetuximab-based therapies.