ERBB2 and breast cancer: Consistent with the SANDPIPER cohort, a similar proportion of clonal multiple PIK3CAmut [405 of 520 (77.9%)] was observed in the subgroup of breast cancer tissue samples that were ERBB2 non-amplified and biopsied from a metastatic site of disease (Additional file 1: Fig. S3), which more closely resembles the trial population.