Chromosome 8 alterations and PTEN loss in Gleason grade 3 tumor to predict the presence of unsampled grade 4 tumor: Implications for active surveillance.

Abstract

93 Background: A key eligibility criterion in many active surveillance (AS) programs is that the biopsy exhibit only Gleason pattern 3 (G3) for a Gleason score of 6 or less. However, 25 to 35% of biopsy Gleason 6 is upgraded to Gleason 7 or higher in the prostatectomy (RP) specimen. Thus, there is a great need for biomarkers that, when measured on G3 tissue in a Gleason 6 biopsy, can predict the presence of unsampled higher grade tumor in the whole prostate. We evaluated PTEN loss by immunohistochemistry (IHC), and PTEN deletion, chromosome 8q (MYC) gain and 8p (LPL) loss by fluorescence in situ hybridization (FISH) for their ability to predict unsampled G4 tumor. Methods: A tissue microarray (TMA) was constructed of RP tissue from three groups of patients (n=50 per group) whose prostates exhibited only Gleason 3+3, only 3+4, or only 4+3 tumor, matched on age, year of RP, and race. In each patient, multiple cores sampled only from areas of G3 were evaluated for PTEN deletion by FISH, PTEN loss by IHC, and chromosome 8p/8q alterations by FISH. Biomarker results were compared between Gleason 6 versus 7 tumors using conditional logistic regression. Results: Patients underwent RP in 2001 to 2009, had median age 60, and median prostate-specific antigen 5.2; 63% of tumors were organ confined. In univariate analyses 8q gain (odds ratio OR=8.9, p<.0001), 8p loss (OR=6.9, p<.0001), PTEN loss by IHC (OR=5.7, p=.025), but not PTEN deletion by FISH (OR=1.5, p=.477) were significantly more common in G3 cores from Gleason 7 tumors than G3 cores from Gleason 6 tumors. In multivariable analyses, 8q gain (OR=6.2, p=.002) and 8p loss (OR=5.2, p=.0002) remained highly significant. At least one high risk biomarker (8q gain, 8p loss, PTEN loss, or PTEN deletion) was found in 35.7% of Gleason 3+3 versus 77.1% of Gleason 3+4 versus 91.3% of Gleason 4+3 tumors, p<.0001. Adjustment for confounding factors did not change the results. Conclusions: Chromosomal 8q gains (MYC), 8p loss (LPL), and PTEN loss measured in Gleason G3 TMA cores strongly differentiate whether the core comes from Gleason 6 or Gleason 7 tumor. If validated in biopsy Gleason 6 cores to predict prostatectomy Gleason 7 tumor these biomarkers could facilitate safe selection of men for active surveillance.