Positive staining for ERG by immunohistochemistry is present in a subset of prostatic small cell carcinomas and correlates with the presence of TMPRSS2-ERG gene fusion.
Overall, 45% (10/22) of prostatic small cell carcinoma cases harbored ERG rearrangements, whereas no cases of bladder or lung small cell carcinomas showed ERG rearrangement (0/12 and 0/13, respectively).
The high prevalence of the TMPRSS2-ERG gene fusion in prostatic small cell carcinoma as well as adenocarcinoma implies that small cell carcinoma may share a common pathogenic pathway with adenocarcinoma in the prostate.
Interestingly, ERG rearrangement in small cell carcinomas occurred exclusively through Edel, supporting the notion that TMPRSS2:ERG with Edel is an aggressive molecular subtype.