Additional markers utilized for characterizing SCLC include B-cell lymphoma 2 (BCL2; frequently expressed), P16 nuclear staining, tyrosine-protein kinase KIT (CD117/c-KIT), retinoblastoma protein (P-RB; consistently negative), and homeobox protein orthopedia (OTP; consistently negative) [41,43]. Here, RB1 is linked to small cell lung carcinoma.