TMPRSS2-ERG rearrangement in dominant anterior prostatic tumours: incidence and correlation with ERG immunohistochemistry.

Aim: To study prostate cancer zonal differences in TMPRSS2-ERG gene rearrangement.

Methods And Results: We examined 136 well-characterized dominant anterior prostatic tumours, including 61 transition zone (TZ) and 75 anterior peripheral zone (PZ) lesions, defined using strict anatomical considerations. TMPRSS2-ERG FISH and ERG protein immunohistochemistry were performed on tissue microarrays. FISH results, available for 56 TZ and 71 anterior PZ samples, were correlated with ERG staining and TZ-associated 'clear cell' histology. Fewer TZ cancers (four of 56; 7%) were rearranged than anterior PZ cancers (18 of 71; 25%) (P = 0.009); deletion was the sole mechanism of TZ cancer rearrangement. ERG protein overexpression was present in 4% (two of 56; both FISH+) and 30% (21 of 71; 17 FISH+) of TZ and anterior PZ tumours, respectively. 'Clear cell' histology was present in 21 of 56 (38%) TZ and eight of 71 (11%) anterior PZ tumours. Seven per cent of cancers with and 21% without this histology had rearrangement, regardless of zonal origin.

Conclusions: TMPRSS2-ERG rearrangement occurs in dominant TZ and anterior PZ prostate cancers, with all rearranged TZ cancers in this cohort showing deletion. ERG immunohistochemistry demonstrated excellent sensitivity (86%) and specificity (96%) for TMPRSS2-ERG rearrangement. TMPRSS2-ERG fusion is rare in TZ tumours and present at a low frequency in tumours displaying 'clear cell' histology.