PIK3CA and neoplasm: Lastly, comparing the somatic alterations between primary and post-NACT residual tumors, we found substantial loss of ERBB2 amplification among the ERBB2+ residual tumor samples after NACT, which has also been seen in other studies.45,46 We also found decrease of TOP2A and PIK3CA alterations among ERBB2+ residual tumors, and a significant increase of PTEN loss among TNBC residual tumors, consistent with previous reports.47,48,49 These alterations point to alternative pathways that could be potential therapeutic targets.