Functional evaluation of plasmin formation in primary breast cancer

Plasmin generation is controlled by the plasminogen activators (PA)/plasmin system, which comprises proteases (urokinase-type PA [uPA] and tissue-type PA [tPA]) and antiproteases (PA inhibitors, PAI-1 and PAI-2). The tumoral content of uPA and PAI-1 has been shown to carry prognostic value in breast cancer; however, because most assays used so far have relied on immunometric determinations, we have explored the enzymatic activities governing plasmin formation in breast cancer specimens.

We applied semiquantitative histochemical zymography to 201 primary breast cancer tissue sections. Enzymatic activities were correlated with histopathologic parameters and clinical outcome. The median follow-up was 91 months.

A wide range of PA-mediated catalytic activities was detected. The overall survival was significantly worse for patients with tumors showing tPA in the lowest quartile of activity (P =.003). The 5-year overall survival of patients with tPA activity in the lowest quartile was 58% compared with 81% for patients with tPA value in the other three quartiles. Tumor size, axillary lymph node metastasis, histologic grade, lymphovascular infiltration, TP53 mutation, and tPA activity were all major risk factors in univariate analysis. tPA activity was an independent prognostic factor in a multivariate Cox regression model, both in the whole population (relative risk = 0.5, 95% confidence interval, 0.3 to 0.9; P =.02) and in the node-negative subgroup (relative risk = 0.2, 95% confidence interval, 0.08 to 0.6; P =.004).

By using a zymographic assay performed directly on primary tumor tissue sections, we demonstrate that reduced tPA-mediated plasmin production is an independent adverse prognostic factor in breast cancer.