SCLC has long been viewed as a homogeneous disease characterized by a set of common pathological features, including a distinct morphology of small cells with scant cytoplasm and ill-defined borders, rapid growth with a high proliferation rate and accompanying necrosis, and near universal loss of both the RB1 (encoding RB) and TP53 (encoding p53) genes. The gene discussed is RB1; the disease is small cell lung carcinoma.