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Summary: Polyclonal antibody to S-100 protein has been routinely applied for initial screening of various types of tumors, including, melanocytic tumors and neurogenic tumors. S-100 protein has been shown to have a broad distribution in human tissues, including renal tubules. The potential utility of S-100 protein in renal cell neoplasms has not been extensively investigated. Using an EnVision–Horseradish Peroxidase (HRP; Dako, Carpinteria, Calif) kit, we evaluated the diagnostic value of S-100 protein on tissue microarray sections from 175 cases of renal epithelial neoplasm (145 primary renal neoplasms and 30 metastatic renal cell carcinomas) and 24 non-neoplastic renal tissues. Immunohistochemical stains for pancytokeratin, HMB-45, and Mart-1 were also performed. Western blot using the same antibody (anti–S-100 protein) was performed on 10 cases of renal cell neoplasm. The results demonstrated that nuclear and cytoplasmic staining pattern for S-100 protein was observed in 56 (69%) of 81 conventional (clear cell) renal cell carcinomas (RCCs), 10 (30%) of 33 papillary RCCs, 1 (6%) of 16 ChRCCs, and 13 (87%) of 15 oncocytomas. Among the 81 cases of CRCC, positivity for S-100 protein was seen in 41 (71%) of 58 and 15 (65%) of 23 cases with Furhman nuclear grade I/II and III/IV, respectively. Focal immunostaining was present in 22 (92%) of 24 normal renal tubules. Similar staining pattern was observed in 21 (70%) of 30 metastatic RCCs. Western blotting demonstrated the S-100 protein expression in both renal cell neoplasm and normal renal tissue. Overexpression of S-100 in oncocytomas compared with ChRCCs was confirmed by the data of Western blot and cDNA microarray analysis. Importantly, 14.8% (12/81) of clear cell RCC and 13.3% (4/30) of metastatic RCC revealed an immunostaining profile of pancytokeratin (−)/S-100 protein (+). These data indicate that caution should be taken in interpreting an unknown primary with S-100 positivity and cytokeratin negativity. In addition, it suggests that S-100 has a diagnostic value in differentiating oncocytoma from ChRCC. [Copyright &y& Elsevier]

Alpha-methylacyl-CoA racemase (AMACR), also known as P504S, is a recently identified molecular marker for prostate cancer. The expression of AMACR/P504S has also been observed in high-grade prostatic intraepithelial neoplasia (PIN), a precursor lesion of prostate cancer. However, a detailed study focusing on the analysis of AMACR/P504S expression in high-grade PIN has not been performed. In this study, we analyzed AMACR/P504S expression by immunohistochemistry in 3954 prostatic ducts and acini with high-grade PIN from 140 prostatectomy specimens. AMACR/P504S immunoreactivity was measured as negative (0), weakly positive (+1), moderately positive (+2), and strongly positive (+3). AMACR/P504S immunoreactivity was detected in 90.0% (126/140) of high-grade PIN cases, although only 41.5% (1642/3954) of prostatic glands involved by PIN showed AMACR/P504S immunoreactivity. A significantly higher AMACR/P504S-positive rate (56.0%) was found in isolated high-grade PIN glands adjacent to cancer (distance less than 5 mm) compared with those away from cancer (distance more than 5 mm; 14%, P < 0.0001). High-grade PIN glands adjacent to cancer also showed a higher (P < 0.0004) AMACR/P504S intensity (1.62) than did those away from cancer (1.11). Our results suggest that PIN strongly positive for AMACR/P504S might be more closely associated with cancer than PIN negative or weakly positive for AMACR/P504S. This study provides additional evidence to link high-grade PIN as a precursor lesion to prostatic adenocarcinoma.

Basal cell proliferation is a common finding in a benign hyperplastic prostate gland. Occasionally, basal cell hyperplasia is so florid that it can be mistaken for prostatic adenocarcinoma. We characterized histological, ultrastructural, and immunohistochemical features of florid basal cell hyperplasia from transurethral resections (n = 11) and prostatectomy specimens (n = 4). Fifteen cases of prostatic adenocarcinoma were used as comparison. Intraluminal calcification was present in 40% of florid basal cell hyperplasia cases (6 of 15) and a unique finding of intracytoplasmic hyaline globules was detected in 53.3% of florid basal cell hyperplasia cases (8 of 15). Ultrastructural analysis revealed luminal calcification and intracytoplasmic electron-dense globules in foci of basal cell hyperplasia. Crystalloids, a frequent finding in low-grade prostate cancer, were absent in all 15 cases of florid basal cell hyperplasia. By immunohistochemistry, the basal cell-specific 34betaE12 and p63 as well as glutathione-s-transferase pi were positive in all basal cell hyperplasia cases but negative in all prostatic adenocarcinomas. These distinguishing features of florid basal cell hyperplasia are helpful in differential diagnosis from prostatic adenocarcinoma. Cytokeratins 8 and 18 were both positive in basal cells, benign secretory cells, and carcinoma cells, failing to be of discrimatory value. Immunostaining for alpha-methylacyl-coenzyme racemase, a new prostate cancer marker, was negative in hyperplastic basal cells but detected a distinct minor benign cell population in basal cell hyperplasia of possible neuroendocrine origin.