Ipsen has suffered another setback in the clinic with the news that the French firm is discontinuing development of its cancer treatment irosustat as monotherapy.

The decision is based on the futility analysis from a Phase II study looking at irosustat monotherapy in endometrial cancer, and on Phase I/II results obtained in metastatic prostate and breast cancers. A review of the former trial demonstrated that the primary endpoint will not be reached (ie patients on treatment for more than 6 months without progression) and that superiority will not be demonstrated with irosustat versus another hormone therapy, megestrol acetate, in terms of progression free survival.

As a result, Ipsen is discontinuing patient recruitment for three clinical trials but it has not given up on irosustat. The drug is a first-in-class orally available irreversible steroid sulfatase (STS) inhibitor and the firm noted that the STS pathway gives rise to oestrone and dehydroepiandrosterone that in turn produce oestradiol and androstenediol that can stimulate the growth of hormone-dependent tumours.

This compound has been tested for postmenopausal metastatic breast cancer as well as castrate-resistant prostate cancer. Trials show that irosustat is well tolerated and with its "potentially encouraging clinical efficacy signal in monotherapy", Ipsen will explore options to develop it in combination with other hormonal therapies in hormone-dependent cancers.

The disappointment over irosustat comes a few months after partner Roche returned the rights to Ipsen for the experimental diabetes drug taspoglutide due to side effects problems.