Karyopharm's drug meets one of two goals in blood cancer trial

By Puyaan Singh and Sahil Pandey

March 24 (Reuters) - Karyopharm Therapeutics KPTI.O said on Tuesday its therapy led to significant reduction in spleen size in a late-stage study of patients with a rare blood cancer, meeting only one of its two main goals.

Shares were down 16% in afternoon trading following the mixed results.

The blood cancer, myelofibrosis, causes scarring in the bone marrow, an enlarged spleen and progressive anemia.

In the 353-patient trial, half of those given Karyopharm's drug Xpovio in combination with Incyte's INCY.O Jakafi saw their spleen size reduced by at least 35% after 24 weeks. In comparison, only 28% of patients who received Jakafi alone saw a similar spleen size reduction.

However, the drug combination failed to meet the study's second main goal of statistically significant symptom improvement.

Given the regulatory precedent of placing significant importance on showing improvement in symptoms, "we think the likelihood of FDA approval is minimal," said Cantor Fitzgerald's Yanni Souroutzidis.

While the company said it was disappointed to miss the goal, the study's principal investigator John Mascarenhas noted that it was probably unrealistic to expect improvement in symptom burden within the 24‑week time frame.

"Deeper spleen responses are really the endpoint of interest," Mascarenhas said in a call with analysts.

Karyopharm also said the combination may help patients live longer, with a preliminary analysis suggesting a more than 50% reduction in risk of death compared with Jakafi alone.

The company said it plans to meet with the U.S. Food and Drug Administration to discuss the results and a potential approval application.

RBC Capital Markets analyst Brian Abrahams was optimistic about the company's prospects. "The data is clearly imperfect, but between spleen, survival, and hints of disease modification, we believe there is enough here to warrant regulatory discussions."

Xpovio, which was first greenlit by the FDA in 2019, is approved to treat other blood cancers, such as types of myeloma and lymphoma.

According to Karyopharm, myelofibrosis affects about 20,000 people in the United States.