56% of the lesions in Rnf20 + /- heterozygous mice showed similar morphological and immunohistochemical characteristics to small cell lung cancer (SCLC), i.e., small cells with scant cytoplasm and densely packed chromatin, which were positive for the calcitonin gene-related peptide (CGRP) and synaptophysin (Syp), markers for small cell lung cancer of neuroendocrine origin34 and negative for CD45, a marker of nucleated hematopoietic cells (Fig. 1a–c, Supplementary Fig. 1h). The gene discussed is PTPRC; the disease is small cell lung carcinoma.