Even within the same organ system, PM incidence varied substantially—evidenced by 29% occurrence in hormone receptor-positive HER2-negative invasive lobular breast carcinoma (ILC HR + HER2−) versus 11% in invasive ductal carcinoma (IDC HR + HER2−), and by 40.7% in microsatellite-stable colorectal cancer (CRC MSS) versus 26.3% in hypermutated CRC (CRC HM). Here, ERBB2 is linked to invasive ductal breast carcinoma.