Final results were announced from the phase 3 PRIMROSE 1 study evaluating the efficacy and safety of linzagolix (Yselty®) for the treatment of heavy menstrual bleeding due to uterine fibroids.

Linzagolix is a novel, oral gonadotropin-releasing hormone (GnRH) receptor antagonist. PRIMROSE 1, a 52-week, double-blind, placebo-controlled study ( NCT03070899), included 526 women with heavy menstrual bleeding associated with uterine fibroids. Patients were randomly assigned to receive linzagolix 100mg or 200mg once daily or placebo, with and without hormonal add-back therapy (ABT) (estradiol 1mg and norethindrone acetate 0.5mg daily). The primary endpoint was the percentage of responders based on menstrual blood loss.

Pooled 52 week data from the PRIMROSE clinical program (PRIMROSE 1 and PRIMROSE 2 [ NCT03070951]) showed that at week 52, linzagolix met the primary endpoint, demonstrating responder rates of 89.3{d847ba2f23daf15c773bda6cb71ac33aa9166b9578a171d654c6e3c528a0b6bc} and 56.4{d847ba2f23daf15c773bda6cb71ac33aa9166b9578a171d654c6e3c528a0b6bc} among women receiving linzagolix 200mg with ABT and linzagolix 100mg without ABT, respectively. Linzagolix also met key clinically relevant secondary endpoints including pain reduction, anemia and quality of life.

At 76 weeks, results showed that off-treatment pain scores remained lower than baseline across all linzagolix treatment arms in PRIMROSE 1; these findings were consistent with those observed in PRIMROSE 2. Moreover, improvements in hemoglobin levels and quality of life were also maintained with linzagolix. Patients treated with linzagolix 100mg and 200mg with ABT also showed evidence of bone mineral density recovery.

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The Company expects to submit a New Drug Application (NDA) to the Food and Drug Administration (FDA) in the third quarter of 2021.


  1. ObsEva announces final results from the phase 3 PRIMROSE program of Yselty® (linzagolix) for the treatment of uterine fibroids. [press release]. Geneva, Switzerland and Boston, MA: ObsEva SA; May 20, 2021. 
  2. ObsEva announces additional phase 3 PRIMROSE 1 and 2 study results confirming sustained efficacy and continued safety of linzagolix in the treatment of uterine fibroids. [press release]. Geneva, Switzerland and Boston, MA: ObsEva SA; December 10, 2020.

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