High frequency of TERT promoter mutation in small cell carcinoma of bladder, but not in small cell carcinoma of other origins

TERT promoter mutations were recently discovered in melanoma by next generation sequencing. Subsequently, several malignancies including urothelial carcinoma were also found to be associated with the same TERT promoter mutations. Small cell carcinoma (SCC) of the urinary bladder is a rare subtype with an aggressive clinical course. Despite the frequent occurrence of TERT promoter mutations in urothelial carcinoma, the incidence of the mutations in SCC of the urinary bladder is unknown. In addition, as a potential molecular marker to distinguish SCC of the urinary bladder from SCC of the prostate, lung (SCLC) and other origins, this information may be clinically useful. We collected a total of 11 cases of SCC of the urinary bladder (10 cases are primary SCC of the urinary bladder; 1 case has primary SCC of the urinary bladder and liver metastasis). We also included 20 cases of SCLC, 2 cases of SCC of the prostate, 5 cases of Merkel cell carcinoma, and 6 cases of SCC from other sites (cervical, GE junction, breast, and soft tissue). In addition, 3 cases of non-neoplastic tissue from the matched SCC of bladder patient and 14 cases of benign urinary bladder were also included. All tumor sections have been examined to confirm the diagnosis and to make sure more than 20% are of tumor content. Genomic DNA was isolated from FFPE tissue and a fragment of the TERT promoter (145 bp) was amplified by PCR. The TERT promoter mutations are determined by bi-directional Sanger sequencing. All (11/11) SCC of the urinary bladder bear TERT promoter mutation C228T. Neither of SCC from all other origins nor matched non-neoplastic tissue contains the TERT promoter mutations. We demonstrated a high frequency TERT promoter mutation in SCC of the urinary bladder, but not in SCC of other origin, such as the prostate. The findings further illustrate molecular differences between SCC of the urinary bladder and SCC of other origins, despite their shared morphologic and immunophenotypic similarities. The TERT promoter mutation may be a biomarker differentiating SCC of the urinary bladder from SCC of other origins.