Urinary bladder biopsy confirmed small cell neuroendocrine carcinoma because tumour cells were positive for synaptophysin, CD56, and chromogranin A. Thus, the patient was diagnosed as having an antitranscriptional intermediary factor 1-<i>γ</i>antibody-positive dermatomyositis concomitant with urinary bladder small cell neuroendocrine carcinoma. This evidence concerns the gene NCAM1 and urinary bladder small cell neuroendocrine carcinoma.