Lack of immunohistochemical detection of VEGF in prostate carcinoma

Vascular endothelial growth factor (VEGF) has been implicated in tumor angiogenesis and is a potential therapeutic target in prostatic adenocarcinoma (PrCa). Immunohistochemical (IHC) analysis has been used to demonstrate VEGF expression in PrCa, and in various other tumors including breast carcinoma, renal cell carcinoma, hepatocellular carcinoma, and gliomas. Prior studies have reported markedly varied VEGF expression in benign prostatic hyperplasia (0% to 100%) and PrCa (40% to 100%). The objective of this study was to measure VEGF expression in PrCa specimens, using IHC analysis with antibodies from different manufacturers and different antigen retrieval techniques.

Cases were identified from an ongoing study analyzing 1270 cases of PrCa diagnosed at various Veterans Health Administration hospitals in the New England region during 1991 to 1995. From this study population, 50 cases (including 40 biopsies, 8 transurethral resections of prostate, and 2 radical resections) were selected. In all cases, tissues were fixed in 10% formalin and embedded in paraffin. Four different antibodies were used for IHC using indirect peroxidase method. For each antibody, different dilutions and antigen retrieval methods (steam with ethylene diamine tetra-acetate, steam with low pH, water bath with target unmasking fluid, trypsin, proteinase K) were tested. EnVision+ system was used to overcome nonspecific staining. Appropriate positive and negative controls were used.

Using different antibodies, positive staining of varying intensity was seen in benign glands, malignant glands, endothelial cells, and fibromuscular stroma. Some cases showed cytoplasmic and granular staining in prostatic glands. However, the staining disappeared in all cases when EnVision+ system was used to block nonspecific staining except for focal and minimal staining in the endothelial cells.

Our results show that when nonspecific staining is blocked, no staining is found for VEGF within the prostate, in either benign or malignant glands. The reasons for the granular and nonspecific staining are unclear at present. Our study may help to explain variable results reported in previous studies, and suggests caution in interpreting VEGF expression in studies of PrCa and benign glands.