Criteria for biopsy diagnosis of minimal volume prostatic adenocarcinoma -Analytic comparison with nondiagnostic but suspicious atypical small acinar proliferation

Context.-Minimal volume prostatic adenocarcinoma (defined as involving less than 5 % of biopsy tissue) is diagnosed increasingly today because of succ essful cancer screening. We previously described the diagnostic category ca lled atypical small acinar proliferation (ASAP), suspicious for but not dia gnostic of malignancy, present in about 2.5 % of routine prostatic needle b iopsy specimens. Objective.-To establish the criteria enabling a distinction between ASAP an d cancer. Design.-We prospectively evaluated clinical and histologic findings from al l 319 patients consecutively diagnosed as having ASAP or minimal cancer by prostatic needle biopsy in a consultation service. Seventeen histopathologi c features were assessed. Results.-Fifty-six patients (18 %) had ASAP, and 100 (31 %) had minimal can cer; the remaining 163 (51 %) had benign diagnoses, high-grade prostatic in traepithelial neoplasia, or larger amounts of cancer. The mean age of patie nts with ASAP did not differ from that of patients with minimal cancer (64. 2 years vs 63.3 years; P = .65). In 10 of 17 histopathologic findings, ASAP differed significantly from minimal cancer. Among architectural findings, ASAP foci averaged 0.4 vs 0.8 mm (P < .0001) and comprised a mean of 11 vs 17 acini (P < .0001). Infiltrative growth occurred in 75 % of ASAP foci and 100 % of minimal cancers (P < .0001). Among cytologic findings, ASAP was s ignificantly less likely than cancer to have mitotic figures (0 % vs 10 %, respectively; P < .01) or prominent nucleoli in at least 10 % of cells (55 % vs 100 %, respectively; P < .0001) and showed more frequent nuclear hyper chromasia (44 % vs 9 %, respectively; P < .0001) and less nuclear enlargeme nt (P = .0002). Luminal blue mucin secretions were less common in ASAP than cancer (6 % vs 33 %, respectively; P < .0001), but eosinophilic granular s ecretions and crystalloids were about equally frequent. Concomitant high-gr ade prostatic intraepithelial neoplasia was present in 23 % of ASAP cases a nd 57 % of cancers (P < .0001). Moderate-to-severe atrophy confounded 59 % of cases with ASAP and 35 % of cancers (P = .003); both ASAP foci and cance r were associated with inflammation in about a quarter of cases. In each ca se with ASAP, we stratified our level of suspicion among 3 categories (favo r benign, uncertain, and favor carcinoma). As suspicion increased so did th e mean nuclear enlargement and percentage of cases with infiltrative growth and nuclear hyperchromasia (all P < .05). Conclusions.-These criteria, which differ significantly between ASAP and mi nimal volume cancer, can help to separate patients for whom a second biopsy is recommended from candidates for prostatectomy or other therapy.