PIK3R1 and invasive breast carcinoma: Normal cells express higher levels of PIK3R1 (which encodes p85α) than of PIK3R2 (p85β) [24, 28, 29]; in contrast, metastatic melanoma, invasive breast cancer and advanced colon carcinoma show a marked increase in PIK3R2 expression, which correlates with tumor grade [24, 25].