Diagnostic utility of PSMA immunohistochemistry in colorectal mass biopsy

Rendering a diagnosis of invasion can be challenging in a small biopsy of a large colorectal mass-forming lesion. However, this diagnosis can have major implications in the management of patients with rectal cancer. Prostate-specific membrane antigen (PSMA) is associated with tumor neoangiogenesis. We compared PSMA expression in biopsies of invasive colorectal cancer (CRC) and in resected adenomas. 65 biopsies from invasive CRC, 48 surgically resected large adenomas and 5 CRC biopsies with sampling error (precursor adenoma was sampled without invasion) were retrieved. PSMA and CD34 immunohistochemistry were performed and the ratio of PSMA+ neovasculature to CD34+ vasculature within the tumors was compared between CRC biopsies and adenomas. In the CRC cohort, clinicopathological characteristics including desmoplasia, the amount of benign/nondysplastic tissue and tumor grade were evaluated for correlation with endothelial PSMA expression. PSMA/CD34 ratio was significantly lower in adenomas (2.8 %) and in CRC biopsies with sampling error (2.5 %) than in CRC biopsies (19.1 %). Using a 5 % cut-off, the sensitivity, specificity, positive, and negative predictive values for accurate diagnosis of CRC were 78.5 %, 83.3 %, 86.4 % and 74.1 %, respectively. A lower PSMA/CD34 ratio was associated with a higher percentage of benign tissue in the biopsy, but no other association was found between PSMA/CD34 ratio and other clinicopathologic parameters. PSMA expression is significantly higher in CRC biopsies than in precursor lesions and adenomas irrespective of the presence of desmoplasia. Our observation indicates that PSMA can serve as an adjunctive tool to confirm invasion in challenging biopsies with inconspicuous desmoplasia.