Intrinsic subtypes, PIK3CA mutation, and the degree of benefit from adjuvant trastuzumab in the NSABP B-31 trial
Katherine L. Pogue-Geile ; Nan Song ; Soonmyung Paik ; Norman Wolmark ; Joseph P. Costantino ; Charles E. Geyer ; D. Lawrence Wickerham ; Sandra M. Swain ; Eleftherios P. Mamounas ; Louis Fehrenbacher ; Priya Rastogi ; Melanie Finnigan ; Nicole L. Blackmon ; Seong-Rim Kim ; Patrick G. Gavin ; Jong-Hyeon Jeong
Journal of Clinical Oncology, Vol.33(12) : 1340~1347, 2015
Journal of Clinical Oncology
PURPOSE: Considerable molecular heterogeneity exists among human epidermal growth factor receptor 2 (HER2) -positive breast cancer regarding gene expression and mutation profiling. Evidence from preclinical, clinical neoadjuvant, and metastatic clinical trials suggested that PIK3CA mutational status and PAM50 intrinsic subtype of a tumor were markers of response to anti-HER2 therapies. We evaluated the predictive value of these two biomarkers in the adjuvant setting using archived tumor blocks from National Surgical Adjuvant Breast and Bowel Project (NSABP) trial B-31.
PATIENTS AND METHODS: Expression data for 49 genes using the nCounter platform were used to generate PAM50 intrinsic subtypes for 1,578 archived tumor blocks from patients in the B-31 trial. Six PIK3CA hotspot mutations were examined by mass spectrometry of the primer extension products in a randomly selected subset (n = 671). We examined the heterogeneity of trastuzumab treatment effect across different subsets defined by each marker using Cox regression and disease-free survival as the end point.
RESULTS: Seven hundred forty-one (47.0%) of 1,578 tumors were classified as HER2-enriched (HER2E) subtype, and 166 (24.7%) of 671 tumors had PIK3CA mutations. Hazard ratios (HRs) for trastuzumab in HER2E and other subtypes were 0.44 (95% CI, 0.34 to 0.58; P < .001) and 0.47 (95% CI, 0.35 to 0.62; P < .001), respectively (interaction P = .67). HRs for trastuzumab in PIK3CA wild-type and mutated tumors were 0.51 (95% CI, 0.37 to 0.71; P < .001) and 0.44 (95% CI, 0.24 to 0.82; P = .009), respectively (interaction P = .64).
CONCLUSION: Unlike results seen in the metastatic and neoadjuvant clinical trials, PIK3CA and PAM50 intrinsic subtypes were not predictive biomarkers for adjuvant trastuzumab in NSABP B-31. These data suggest that results from the metastatic and neoadjuvant setting may not be always applicable to the adjuvant setting.