What happened

Cancer drug specialist Curis (CRIS -5.11%) had a Friday to forget. The biotech's share price took a nearly 37% hit after the company reported some disquieting news about a leading pipeline drug.

So what

Friday morning, Curis published updated data from a phase 1/2 clinical trial of its CA-4948, a drug targeting acute myeloid leukemia and myelodysplastic syndromes. The primary endpoint of the trial, which involved 22 participants, was to determine the treatment's maximum tolerated and recommended dose for a phase 2 study.

Cancer attacking an organism.

Image source: Getty Images.

In the trial, the orally administered monotherapy showed dose-limiting toxicities and was administered in 200, 300, 400, and 500 milligram versions. The latter two showed toxicities, therefore Curis decided the upcoming phase 2 trial will involve the 300 milligram dose.

In the update, the biotech's CEO James Dentzer pointed out that the new data "further support the growing body of evidence that CA-4948's anti-cancer activity continues to deepen the longer patients remain on drug, which is enabled by its safety and durability profile to date."

Now what

While such words are encouraging, it's clear investors are deeply concerned about those toxicities. Previously, CA-4948 had seemed to hold more promise -- an earlier-stage study involving nine individuals showed a reduction of abnormal white blood cells in eight of them. That was greeted positively by a hopeful market, but that was then and this is now, and it seems investors are losing that hope.