The pathology of incidental carcinoma.

"Incidental" cancer refers to predominantly well differentiated cancer that arises in the transition zone and is found by chance in TURP chips. These tumours are frequently small and may be completely resected by TURP, although a significant number have an additional tumour that is unreachable with a resectoscope. These tumours often co-exist with benign prostatic hyperplasia. Putative precursors of incidental carcinoma include high grade PIN and AAH, and these lesions are frequently found in the transition zone in prostatectomies for cancer. The single most significant question in treating incidental adenocarcinoma is how to separate tumours that will progress from those that will not progress during the expected lifetime of the patient. The 1992 revision of the TNM staging system separated non-aggressive (T1a) and aggressive (T1b) incidental cancer according to the number of foci of cancer, using more than three foci as the cutpoint to identify more aggressive cancer. However, 8-37% of patients with T1 a cancer will develop cancer progression within 10 years if untreated, with the risk of progression increasing with additional years of follow-up. Important prognostic factors include the patient's age, tumour location (peripheral zone v. transition zone), tumour grade, tumour volume, serum PSA concentrations and morphometric factors such as nuclear roundness. Studies directed at early detection allow discovery of increasingly smaller cancers.