Diagnosis of "suspicious for malignancy" in prostate biopsies: predictive value for cancer

Prostate needle biopsies occasionally contain an atypical small acinar proliferation (ASAP) that is suspicious for but not diagnostic of malignancy. The predictive value of ASAP for cancer has not been studied in a large series.

To determine the reproducibility and clinical significance of ASAP in a large urologic reference laboratory, we retrospectively studied 295 patients with ASAP diagnosed from 1991 to 1995. Each patient had at least one follow-up biopsy. Mean patient age was 68.0 years (range 40 to 89). Numerous clinical and histologic features were assessed to determine their predictive value for malignancy on subsequent biopsy.

Adenocarcinoma was identified on follow-up biopsy in 125 patients (42%), with a median follow-up of 5.7 months (range 0.1 to 43). Gleason score varied from 4 to 9 (mean 6.2). Cumulative detection of 125 cancers was 90% after second biopsy and 99% after third biopsy. Serum prostate-specific antigen, digital rectal examination result, and patient age were not predictive of cancer on follow-up biopsy. Likewise, the number of biopsy cores and histologic findings including number of acini per focus of ASAP, number of foci of ASAP, degree of nuclear and nucleolar enlargement, and presence of luminal pink granular secretions, mucin, or crystalloids were not predictive of cancer. Stratifying our level of suspicion into three categories (favor benign, uncertain, and favor carcinoma) did not differentially predict subsequent cancer (44%, 44%, and 41% of patients, respectively; P = 0.86) nor the percentage of tissue involved by cancer. No clinical or pathologic feature affected the likelihood of subsequent cancer. In 39% of patients, cancer was only contralateral to or in a different sextant site from the initial ASAP site.

The high predictive value of ASAP for subsequent adenocarcinoma warrants repeat biopsy. Sampling should include multiple sites in the prostate.