For instance, in the AJCC Cancer Staging Manual (8th edition),1 the stage groups of invasive carcinoma of the breast now include grade (G), estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor‐2 (HER2), in addition to the traditional primary tumor (T), regional lymph nodes (N), and distant metastasis (M). Here, PGR is linked to cancer.