RB1 and neuroendocrine carcinoma: All NEC or NEC components of mixed NEC/IDC-NST harboring RB1 alterations (including frameshift and splice site mutations, deep deletions, and genomic rearrangement) were RB negative by immunohistochemistry, including all SCNEC (6/6) and ANEC (2/2), and 2/4 LCNEC.