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Background: The aromatase inactivator exemestane may cause clinical disease stabilization following progression on non-steroidal aromatase inhibitors like letrozole in patients with metastatic breast cancer, indicating that additional therapeutic effects, not necessarily related to estrogen-suppression, may be involved in this well-known “lack of cross-resistance”. Experimental design: Postmenopausal women with ER positive, HER-2 negative, locally advanced breast cancer were enrolled in the NEOLETEXE-trial and randomized to sequential treatment starting with either letrozole (2.5 mg o.d.) or exemestane (25 mg o.d.) followed by the alternative aromatase inhibitor. Serum levels of 54 cytokines, including 12 adipokines were assessed using the Luminex xMAP technology (multiple ELISA). Results: Serum levels of leptin were significantly decreased during treatment with exemestane (p < 0.001), regardless whether exemestane was given as first or second neoadjuvant therapy. In contrast, letrozole caused a non-significant increase in serum leptin levels in vivo. Conclusions: Our findings suggest an additional and direct effect of exemestane on CYP-19 (aromatase) synthesis presumably due to effects on the CYP19 promoter use that is not present during therapy with non-steroidal aromatase inhibitors. Our findings provide a reasonable explanation for the clinically observed lack of cross-resistance between nonsteroidal and steroidal aromatase inhibitors in breast cancer patients.Trial registration: registered on March 23rd. 2015 in the National trial database of Norway (Registration number: REK-SØ-84-2015). |
