1. ¹Department of Pathology, The Johns Hopkins Medical Institutions, Baltimore, Maryland, USA
2. ²Department of Urology, The Johns Hopkins Medical Institutions, Baltimore, Maryland, USA
3. ³Department of Oncology, The Johns Hopkins Medical Institutions, Baltimore, Maryland, USA
4. ⁴The Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA

Correspondence: Dr GJ Netto, Department of Pathology, The Johns Hopkins Hospital, 401 N Broadway, 2242 Weinberg Bldg, Baltimore, MD 21231, USA. E-mail: gnetto1@jhmi.edu

Received 22 April 2009; Revised 8 July 2009; Accepted 21 July 2009; Published online 4 September 2009.

Abstract

Minute prostatic adenocarcinomas are considered to be of insufficient virulence. Given recent suggestions of TMPRSS2–ERG gene fusion association with aggressive prostatic adenocarcinoma, we evaluated the incidence of TMPRSS2–ERG fusion in minute prostatic adenocarcinomas. A total of 45 consecutive prostatectomies with minute adenocarcinoma were used for tissue microarray construction. A total of 63 consecutive non-minimal, Gleason Score 6 tumors, from a separate PSA Era prostatectomy tissue microarray, were used for comparison. FISH was carried out using ERG break-apart probes. Tumors were assessed for fusion by deletion (Edel) or split (Esplit), duplicated fusions and low-level copy number gain in normal ERG gene locus. Minute adenocarcinomas: Fusion was evaluable in 32/45 tumors (71%). Fifteen out of 32 (47%) tumors were positive for fusion. Six (19%) were of the Edel class and 7 (22%) were classified as combined Edel+Esplit. Non-minute adenocarcinomas (pT2): Fusion was identified in 20/30 tumors (67%). Four (13%) were of Edel class and 5 (17%) were combined Edel+Esplit. Duplicated fusions were encountered in 5 (16%) tumors. Non-minute adenocarcinomas (pT3): Fusion was identified in 19/33 (58%). Fusion was due to a deletion in 6 (18%) tumors. Seven tumors (21%) were classified as combined Edel+Esplit. One tumor showed Esplit alone. Duplicated fusions were encountered in 3 (9%) cases. The incidence of duplicated fusions was higher in non-minute adenocarcinomas (13 vs 0%; P=0.03). A trend for higher incidence of low-level copy number gain in normal ERG gene locus without fusion was noted in non-minute adenocarcinomas (10 vs 0%; P=0.07). We found a TMPRSS2–ERG fusion rate of 47% in minute adenocarcinomas. The latter is not significantly different from that of grade matched non-minute adenocarcinomas. The incidence of duplicated fusion was higher in non-minute adenocarcinomas. Our finding of comparable rate of TMPRSS2–ERG fusion in minute adenocarcinomas may argue against its value as a marker of aggressive prostate carcinoma phenotype.