PIN-like (Ductal) Adenocarcinoma of the Prostate

Prostatic intraepithelial neoplasia like (PIN-like ductal) carcinoma are rare tumors characterized by crowded, often cystically dilated glands architecturally resembling high-grade prostatic intraepithelial neoplasia, lined by malignant pseudostratified columnar epithelium. The largest prior series studied 9 radical prostatectomies (RPs) and suggested a behavior similar to Gleason score 6. We sought to investigate this rare tumor within a larger series. PIN-like carcinoma cases were identified from in-house and consultation files from 2008 to 2017. A total of 190 total cases were identified (in-house cases n=8, 4.2%, consult cases n=182, 95.8%); the diagnosis of PIN-like carcinoma was made on needle biopsy (n=181), transurethral resection (n=5) and RP (n=4). The average age was 70 years. The average number of cores with involvement by PIN-like carcinoma was 2 (1 to 12). The average maximum percentage by a PIN-like carcinoma component of any core was 43.5% (5% to 90%). In 58/181 (32.0%) biopsy cases, due to selective parts having been submitted for consultation, it was unknown whether there was an association with acinar carcinoma. A total of 72 cases showed exclusively PIN-like carcinoma. Highest grade groups (GGs) on biopsies with known acinar or papillary/cribriform ductal carcinomas were GG1 (n=23, 45.1%), GG2 (n=14, 27.5%), GG3 (n=9, 17.6%), GG4 (n=4, 7.8%), and GG5 (n=1, 2.0%). Of 44 cases where the patient would be considered eligible for active surveillance, 18 (41.0%) underwent RP. RP slides were available in 16 cases; 3 (18.8%) cases diagnosed on biopsy did not show PIN-like carcinoma on review of RP slides. PIN-like carcinoma was present without an associated acinar tumor in 3 (23.1%) RPs; 2 showing tumors with large, cystic dilated glands extending into periprostatic tissue. In 7/13 cases (53.8%), the acinar component was the dominant tumor and the PIN-like carcinoma component was small (<1 cm). The overall grade at RP was GG1 (5/13, 38.5%) and GG2 (8/13, 61.5%). In all cases with an acinar component, the acinar tumor was anatomically distinct from the PIN-like carcinoma tumor. The GGs of the separate acinar tumors were GG1 (6/10) and GG2 (4/10) with percent pattern 4 ≤5% in all 4 cases. No cases were associated with metastases to lymph nodes or seminal vesicle invasion. Extraprostatic extension was present in 6/13 (46.1%) cases, from the acinar component in 1 (7.7%) case and the PIN-like carcinoma component in 5 (83.3%) cases. In all 5 cases, there was a peculiar morphology of thin papillary projections into cystic dilated PIN-like carcinoma glands. Immunohistochemical expression of ERG was positive in 1/11 (9.1%) case. 1/11 (9.1%) case showed heterogeneous loss of PTEN. Overall, PIN-like carcinoma tumors are limited in size, not advanced in stage, not associated with high-grade cancer on RP, and show low rates of Gleason pattern 4 and TMPS-ERG rearrangement. Our study supports grading classic PIN-like carcinoma as Gleason pattern 3; at the current time we recommend grading thin papillary projections of PIN-like carcinoma as pattern 4. Longer term studies will be needed to determine the clinical significance of thin papillary projections in PIN-like carcinoma.