Small Cell Carcinoma of the Urinary Bladder: KIT and PDGFRA Gene Mutations

Primary small cell carcinoma of the urinary bladder is very rare. A 72-year-old was admitted to our hospital because of hematuria and dysuria. Cystoscopy revealed a bladder full of multiple, solid and papillary tumors. Biopsies from the deep and papillary tumors were taken. Histologically, tumor was pure small cell carcinoma. Immunohistochemically, the tumor cells were positive for cytokeratin, chromo-granin, synaptophysin, neuron-specific enolase, CD56, CD117 and Ki67 (labeling 70%). The tumor cells were negative for CK7, CK20, CD3, CD20, LCA, CDX2, uroplakin, thyroid transcription factor 1, PSA and p63. Metastatic workup was performed an no primary or metastatic lung lesions were noted. Due to the clinical, radiologic and immunohistochemical findings, the patient was diagnosed as primary small cell carcinoma of bladder. A molecular genetic analysis for KIT (exons 9, 11, 13 and 17) and PDGFRA (exons 12 and 18) genes was performed, in paraffin micro dissection specimens, by the PCR-direct sequencing method. According to the sequencing analyses, two mutations were found at positions 558 (p.K558N) and 562 (p.E562D) in KIT gene exon 11 in our case. The another hand the same case presented two mutations in PDGFRA gene exon 14 at position 631 (p.P631A) and 638 (p.638Q_639AinsC). The disease process was fulminant and the patient was lost due to several complications prior to any chemotherapy.