Cathepsin B expression is similar in African-American and Caucasian prostate cancer patients

Increased incidence and mortality of prostate cancer (PCa) suggest that U.S. African-American men have more invasive cancer than Caucasian men. Invasive PCa requires several proteases, including the cysteine protease cathepsin B (CB), for degradation of basement membrane and extracellular matrix proteins prior to cancer cell migration across biological compartments. Our objective was to determine whether CB immunostaining patterns, in relation to clinical data, could distinguish invasive PCa in African-American and Caucasian patients.

Fifty Gleason score 6/7 PCa cases were selected for similar clinical data with benign prostatic hyperplasia (BPH) samples as controls. Immunostainings were imaged directly from microscope slides to a computer using a digital camera. Data were quantified using Metamorph software, analyzed using the two-sample t-test and confirmed by multiple regression.

Ratios of CB to its endogenous inhibitor stefin A (SA) immunostainings were greater in PCa than BPH, but were not significantly different in PCa of either race. The African-American patients did not show increased CB immunostaining, indicating that the contribution of this protease to invasiveness was similar in both races.

When veterans received equal medical care at the Minneapolis Veterans Affairs Medical Center, African-American patients did not show increased PCa invasiveness. Our conclusion is supported by analysis of post-surgery serum total PSA levels and cancer cell invasion to margins/capsules, seminal vesicles and/or lymph nodes. Invasiveness of PCa does not appear to be race-dependent. The previous conclusion of race-based differences in PCa requires re-evaluation with respect to the role of proteases (such as CB, matrix metalloproteinase) in invasion and metastasis of cancer cells.