Assessing the order of critical alterations in prostate cancer development and progression by IHC: further evidence that PTEN loss occurs subsequent to ERG gene fusion

Abstract

Background ERG rearrangements and PTEN loss are two of the most common genetic alterations in prostate cancer. However, there is still significant controversy regarding the order of events of these two changes during the carcinogenic process. We used IHC to determine ERG and PTEN status and calculated the fraction of cases with homogeneous/heterogeneous ERG and PTEN staining in a given tumor. Methods and Results Using a single standard tissue section from the index tumor from radical prostatectomies (N= 77), enriched for relatively high grade and stage tumors, we examined ERG and PTEN status by IHC. We determined whether ERG or PTEN staining was homogeneous (all tumor cells staining positive) or heterogeneous (focal tumor cell staining) in a given tumor focus. 57% (N=44/77) of tumor foci showed ERG positivity, with 93% of these (N=41/44) cases showing homogeneous ERG staining in which all tumor cells stained positively. 53% (N=41/77) of tumor foci showed PTEN loss, and of these, 66% (N=27/41) showed heterogeneous PTEN loss. In ERG homogeneously positive cases, any PTEN loss occurred in 56 % (N=23/41) of cases, and of these, 65% (N=15/23) showed heterogeneous loss. In ERG negative tumors, 51.5% (N=17/33) showed PTEN loss, and of these, 64.7% (N=11/17) showed heterogeneous PTEN loss. In a subset of cases, genomic deletions of PTEN were verified by FISH in regions with PTEN protein loss as compared to regions with intact PTEN protein, which did not show PTEN genomic loss. Conclusions These results support the concept that PTEN loss tends to occur as a subclonal event within a given established prostatic carcinoma clone after ERG gene fusion. The combination of ERG and PTEN IHC staining can be used as a simple test to ascertain PTEN and ERG gene rearrangement status within a given prostate cancer in either a research or clinical setting.

Identification of Combinatorial Genomic Abnormalities Associated with Prostate Cancer Early Recurrence

“…10 In the current cohort, prostate cancer tumors had more heterogeneous results in PTEN FISH compared with TMPRSS2/ERG FISH. Similar findings were reported using IHC assessment 17 : most ERG-positive radical prostatectomy samples had homogeneous ERG staining, whereas more than half of the PTEN loss samples had heterogeneous staining. Together, these observations support the theory that TMPRSS/ERG rearrangement is an early event of prostate carcinogenesis, whereas PTEN deletion is more likely a later event and hence associated with advanced diseases.…”

A Prospective Investigation of PTEN Loss and ERG Expression in Lethal Prostate Cancer

“…Tumor fusion status is not associated with lethal progression in most studies (22), but our group recently presented the first evidence that tumor fusion status may modify the association of prostate cancer risk factors with lethal prostate cancer progression (23). PTEN loss is more common in fusion-positive compared with fusion-negative disease (10,(24)(25)(26)(27), and PTEN loss almost certainly occurs subsequent to ERG rearrangement (19,28,29). Thus, presence of the TMPRSS2:ERG gene fusion may modify the effects of PTEN loss on disease progression.…”

“…PTEN is most commonly lost by deletion, which is frequently a focal and subclonal event in primary prostate tumors (10,19,20), making reliable detection difficult by methods requiring nucleic acid extraction or fluorescence in situ hybridization (FISH). Addressing this issue, our group previously optimized an immunohistochemistry (IHC) assay for in situ PTEN protein detection in prostate cancer (6).…”

Combination of Multiple Markers Predicts Prostate Cancer Outcome

“…This significant finding remained after adjusting for clinical variables and further supports the role of ERG and PTEN in PCa progression, but did not reach statistical significance when evaluating the loss of PTEN protein expression in the same manner as above mentioned combinations with PTEN deletion. The sequential order of ERG rearrangements and PTEN aberrations is currently unsolved but [6,[19][20][21] concurrent ERG rearrangement and PTEN loss have been shown to promote PCa [5,6] and have been associated with PCa outcome. Leinonen et al found that patients harboring aberrant ERG with simultaneous PTEN loss, were associated with shorter progression-free survival [8] and Yoshimoto et al, found the combination to be predictive of earlier biochemical recurrence [7], supporting the results found in this study.…”