PTEN loss in Gleason grade 7 prostate tumors exhibits intratumoral heterogeneity and is associated with unfavorable pathological features

ABSTRACT

Background: PTEN loss is observed in 20­30% of prostate cancers and is associated with a poor outcome, but clinical details of the impact of this biomarker are unclear for intermediate grade tumors. Methods: We investigated 43 radical prostatectomy-derived grade 7 prostate tumors from the Clinics Hospital of Ribeirão Preto. Tissue microarray (TMA) blocks were constructed and PTEN copy number status was determined for all patients through fluorescence in situ hybridization (FISH). To determine the presence of PTEN protein loss in our study cohort, we performed immunohistochemistry (IHC) in TMA sections. We then developed an automated algorithm in HALO™ to identify regions of PTEN protein loss in whole prostate scanned sections from ten patients with known PTEN deletion status by FISH. Clinical analyses were conducted to determine the associations between PTEN loss and patient outcome. All statistical analyses were conducted in R v3.4.3 with P-values below 0.05 being considered statistically significant. Results: In this study of 43 grade 7 tumors, we found PTEN deletions by FISH in 18.9% of tumors, and PTEN protein loss by IHC in 16.3% of tumors. Both techniques were highly concordant and complementary. Clinical analysis demonstrated that PTEN deletion by FISH was significantly associated with positive margin invasion (P = 0.04) and Gleason score upgrade (P = 0.001). Digital image analysis of ten representative tumors demonstrated distinct intratumoral heterogeneity for PTEN protein loss in four tumors. Conclusions: This study shows that PTEN loss in Gleason grade 7 tumors can be heterogeneous and that a systematic analysis of this biomarker using a combination of FISH, IHC, and digital imaging may identify patients with a greater risk of poor outcome (AU)