Leuprorelin combined with letrozole with/without everolimus in ovarian-suppressed premenopausal women with hormone receptor-positive, HER2-negative metastatic breast cancer: The LEO study.

PURPOSE: In the randomised phase II LEO trial, we investigated the effect of adding everolimus (EVE) to letrozole (LET) in ovarian-suppressed premenopausal women with hormone receptor-positive (HR+), HER2-negative (HER2-) recurrent/metastatic breast cancer.

METHODS: Patients with progression or prior exposure to tamoxifen with or without gonadotropin-releasing hormone agonists, either sequentially or concurrently, in adjuvant or metastatic setting were randomly assigned (2:1) to the EVE arm (leuprorelin + LET + EVE) or the LET arm (leuprorelin + LET) until disease progression or unacceptable toxicity. The primary end-point was progression-free survival (PFS). Secondary end-points included overall survival (OS), objective response rate (ORR), clinical benefit rate (CBR) and safety.

RESULTS: Between January 2014 and October 2018, 137 patients were enrolled (median age, 44 years [range, 24-56]). Of them, 75% had endocrine-sensitive disease, and 61% had visceral metastasis. With the median follow-up of 32.4 months, the median PFS was 18.1 months in the EVE arm and 13.8 months in the LET arm (HR 0.73, P = 0.137). Among patients with visceral metastases, the median PFS was significantly longer in the EVE arm (16.4 versus 9.5 months, P = 0.048). The median OS was not reached in both arms. The CBR was significantly higher in the EVE arm (83% versus 62%, P = 0.010). The ORR was similar between the two arms. The most common grade 3/4 adverse events in the EVE arm were neutropenia, alanine aminotransferase elevation and anaemia.

CONCLUSIONS: EVE plus LET with ovarian-suppression resulted in longer PFS in tamoxifen-exposed HR+, HER2- metastatic breast cancer patients with visceral metastasis.