Differential expression of uninary plasminogen activator, its receptor and inhibitor in ductal carcinoma in situ assessed by immunohistochemistry and in situ hybridization

The urinary plasminogen activator (u-PA) system comprised of u-PA, its receptor (u-PAR) and inhibitor (PAI-1) has been implicated in the progression of invasive breast cancer. Its role in non-invasive breast cancer is not well understood. We hypothesize that expression of u-PA is an early event in the progression of breast tumors. To test this hypothesis, we examined the expression of u-PA, u-PAR and PAI-1 in ductal carcinoma in situ (DCIS). Paraffin-embedded sections of 36 DC1S tumors (18 comedo and 18 non-comedo) were stained with monoclonal antibodies against u-PA (3689), u-PAR (3932) and PAI-1 (3785) using a biotin - avidin - HRP system in a Ventana automated staining system. Fluorescein in situ hybridization (FISH) to detect u-PA-mRNA was performed on five tumors. u-PA was expressed in 34/36 (94%) tumors, whereas u-PAR was only expressed in 14 (39%). PAJ-1 on the other hand was expressed in 3/36 (8%) of in situ carcinomas all of which were comedo. u-PA and u-PAR were co-expressed in the tumor ductal epithelium of 13/36 in situ tumors (five comedo, eight non-comedo). Of 36 DCIS tumors, 28 lacked peritumoral stromal staining for u-PA, 3 3 for u-PAR and 28 for PAI-1. Only eight tumors demonstrated peritumoral strornal staining for u-PA. Surprisingly, peritumoral staining for u-PA was strong in low-grade and weak in highgrade tumors. Peritumoral stromal staining for PAI-1 was lost in 28/36 tumors, although the tumors strongly expressed u-PA and to a lesser extent u-PAR. Stroma surrounding the normal ducts stained strongly for PAI-1 (n= 28/36). Of the five tumors evaluated by FISH, u-PA-mRNA was found in the tumor epithelial cytoplasm but not in the surrounding stroma. Neither normal ducial epithelium nor its surrounding stroma expressed u-PA-mRNA. We conclude that: (1) Expression of u-PA appears to be an early event in DCIS progression followed by a later expression of u-PAR, (2) PAI-1 expression is down-regulated in the peritumoral stroma but not in the stroma surrounding the normal ducts, during this early event, (3) in situ hybridization studies with u-PA c-DNA suggest that tumor progression of DCIS occurs by an autocrine mechanism.