PIK3CA and neoplasm: In our primary analysis, patients with a tumor with either a PIK3CA exon 9 or exon 20 mutation did not derive significant benefit from tamoxifen (HR, 0.82 (95% CI, 0.22 to 3.04) and 0.77 (95% CI, 0.25 to 2.36), respectively (Table 3 and Additional file 1: Table S9) However, the interaction between PIK3CA mutations and tamoxifen was not significant.