TMPRSS2-ERG Fusions Unexpectedly Identified in Men Initially Diagnosed With Nonprostatic Malignancies

Abstract

Purpose TMPRSS2-ERG gene fusions are frequently found in prostate cancer and are pathognomonic for prostatic origin. In a series of cancer cases assayed with comprehensive genomic profiling (CGP) in the course of clinical care, we reviewed the frequency of TMPRSS2-ERG fusions in patient tumors of various histologic subtypes. Methods Frequency of TMPRSS2-ERG fusions was determined in CGPs from 64,263 cancer cases submitted to Foundation Medicine to assess genomic alterations suggesting benefit from targeted therapy. Genomic results are presented from an index case of prostate cancer that underwent evolution from adenocarcinoma to pure squamous cell carcinoma. Results TMPRSS2-ERG fusions were identified for 0.86% of male patients (250 of 29,030) and not found for female patients (none of 35,233). TMPRSS2-ERG fusions were detected in six tumors classified as squamous carcinoma, five of which were of unknown primary site. The index case is a patient with a large, left retrovesical mass diagnosed as squamous carcinoma by morphologic examination and a history of Gleason score 9 prostate cancer with prior prostatectomy and salvage radiation therapy. TMPRSS2-ERG was detected by genomic profiling in the squamous cell tumor, the primary adenocarcinoma of the prostate, and in a metachronous prostatic adenocarcinoma metastasis. On the basis of these results, the patient received androgen deprivation therapy. A phylogenetic tree demonstrating clonal and histopathologic evolution of prostate cancer in the index patient was constructed. Conclusion In this large CGP dataset, TMPRSS2-ERG fusion was seen in approximately 30% of prostate cancers regardless of histologic type; on occasion, the fusion was detected in advanced cancers not initially carrying a diagnosis of prostate carcinoma. CGP of advanced cancers in men may reveal prostatic origin by detection of the pathognomonic TMPRSS2-ERG fusion gene.