PCA3 (Prostate CAncer gene 3) is a gene which is prostate cancer specific. Unlike prostate specific antigen (PSA), PCA3 is only produced by PCa cells and not affected by prostate size. It discriminates better than PSA between PCa and benign/non-cancerous prostate diseases such as benign prostatic hyperplasia (BPH, i.e. prostate enlargement) or prostatitis (infection of the prostate). Therefore, it is an additional tool in deciding if prostate biopsy is really needed.

More info: PCA3 background information