Detection of prostate-specific membrane antigen expressing cells in blood obtained from renal cancer patients: A potential biomarker of vascular invasion

Originally, prostate-specific membrane antigen (PSMA) was described in beni gn and malignant prostate cells. On the basis of recent reports that this a ntigen also is expressed in normal renal proximal tubular cells and in the neovascular endothelium associated with renal carcinoma, we used a nested r everse transcriptase-polymerase chain reaction assay to evaluate whether PS MA-expressing cells might be present in specimens of peripheral blood obtai ned from renal cancer patients, benign renal tumor patients, and healthy vo lunteers. Our reverse transcriptase-polymerase chain reaction PSMA assay ha d a sensitivity of detecting 1 lymph node prostate cancer (LNCaP) per 10(7) lymphocytes. None of the 20 non-renal cancer controls were positive for PS MA mRNA, whereas 11 of 50 patients (22%) with diagnosed renal cancer were p ositive. Despite a comparative increase of PSMA positivity with stage, no s tatistical correlation was found. However, 44% of PSMA-positive patients ha d tumor size greater than 12 cm, versus only 9% in patients negative for PS MA (P =.03), and 67% of positive PSMA patients were found to have vascular invasion versus only 16% of patients negative for PSMA (P =.006; odds ratio , 10.8). This preliminary study suggests the possibility that PSMA expressi on in peripheral blood might be a useful biomarker for detecting or monitor ing the progression of renal cancer in patients.