Urokinase-type plasminogen activator and its inhibitor PAI-1: predictors of poor response to tamoxifen therapy in recurrent breast cancer.

BACKGROUND

Urokinase-type plasminogen activator (uPA) is a proteolytic enzyme thought to be involved in processes leading to tumor cell invasion of surrounding tissues. Its activity during metastasis may be regulated by an inhibitor, PAI-1. Previous work has shown that high levels of uPA and PAI-1 are associated with poor prognosis in primary breast cancers.

PURPOSE

In this pilot study, we explored possible associations between the expression levels of uPA or PAI-1 and the efficacy of tamoxifen treatment in breast cancer patients with relapsed disease.

METHODS

Levels of uPA, PAI-1, estrogen receptor (ER), and progesterone receptor (PgR) were assayed in cytosolic extracts derived from the primary breast tumors of 235 tamoxifennaive patients who had recurrent disease. The extracts were classified as positive or negative for each assayed factor. In some analyses, ER and PgR levels were evaluated together. In these analyses, three ER/PgR subsets were defined: low, intermediate, and high. All patients in the study received tamoxifen therapy upon relapse (median follow-up, 57 months). Association of the tested factors with the response to tamoxifen treatment was studied by logistic regression analysis. Association of the factors with progression-free and overall survival was further evaluated by Cox univariate and multivariate regression analyses.

RESULTS

Patients with uPA-negative tumors exhibited a better response (tumor regression or stable disease, maintained for more than 6 months) to tamoxifen treatment than those with uPA-positive tumors (51% versus 26% response; odds ratio [OR] = 0.34; 95% confidence interval [CI] = 0.18-0.65). The response rate was also better for patients with PAI-1-negative tumors than for those with PAI-1-positive tumors (49% versus 35% response; OR = 0.57; 95% CI = 0.32-1.01). In addition, patients with uPA-positive or PAI-1-positive tumors showed shorter progression-free survival (P = .001 and P < .05, respectively) and total survival after relapse (P = .005 and P < .005, respectively). When patients were stratified by ER/PgR status, the only statistically significant association between uPA levels and reduced tamoxifen response was seen in the subset whose tumors possessed intermediate levels of ER/PgR (16% response in uPA-positive versus 60% response in uPA-negative tumors; OR = 0.13; 95% CI = 0.04-0.41). Overall, uPA status appeared independent of association with ER/PgR status in its ability to predict response to tamoxifen treatment. The association of PAI-1 expression and the response to tamoxifen was less pronounced when patients were stratified by ER/PgR status.

CONCLUSION

Measurement of primary breast tumor uPA levels may be useful in predicting the overall response of metastatic disease to tamoxifen therapy.