PIK3CA and neoplasm: To dissect drivers of response, we performed scRNA‐seq on tumour biopsies collected at baseline (pretreatment, d1) and at the time of sacrifice (posttreatment, d30 or whenever tumours reached a volume of 2000 mm2) from n = 14 CD34+ humanized EMC041 PDXs (n = 3 vehicle, n = 3 PD‐1i, n = 4 PI3K/mTORi, n = 4 PI3K/mTORi+PD‐1i).