The identification of pathogenic germline RAD51AC defects in a thymic neuroendocrine tumor [78], as well as a germline APC variant harboring breast carcinoma patient with a pulmonary neuroendocrine tumor [90] and a germline MSH2 variant of unknown significance in another breast carcinoma patient with well-differentiated pulmonary neuroendocrine tumor [90], expands the spectrum of non-syndromic manifestations of germline disease in well-differentiated thoracic neuroendocrine neoplasms. The gene discussed is APC; the disease is breast carcinoma.