ERBB2 and breast cancer: Between January 1, 2015 and December 31, 2021, 674 men with breast cancer were reported to the Cancer Registry of Baden-Württemberg (as depicted in Fig. 1 below), 397 of whom were patients with early breast cancer: 354 (89.2%) had a HR + /Her2−, 39 (9.8%) a Her2 + , and 4 (1.0%) a triple-negative tumor subtype.