MorphoSys AG (NASDAQ:MOR) is reportedly facing a burgeoning safety concern surrounding pelabresib, an experimental myelofibrosis treatment.

Myelofibrosis is a type of blood cancer characterized by the buildup of scar tissue, called “fibrosis,” in the bone marrow.

Physicians participating in MorphoSys’ Phase 3 study have observed instances when patients treated with pelabresib swiftly transitioned from myelofibrosis to acute myeloid leukemia (AML), a more aggressive form of blood cancer.

Citing sources familiar with the cases, STAT News noted physicians saw several instances of patients undergoing such rapid progression. 

Among 212 patients receiving pelabresib, six serious safety events of “AML transformation” were reported, compared to only two events among 214 patients in the control group.

The deal is expected to close in the first half of 2024.

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The FDA was alerted about this imbalance in severe cancer advancements. It issued a cautionary letter to all physicians involved in the study and is closely monitoring the situation. 

Despite this setback, MorphoSys affirmed its acquisition by Novartis is still on track to finalize in the first half of this year.

“We generally do not discuss our interactions with regulatory authorities publicly. We remain confident in the benefit-risk profile of the combination of pelabresib and ruxolitinib,” a Morphosys spokesperson said in an emailed response to Reuters.

“The planned acquisition by Novartis is progressing steadily,” they added.

In November, the company released topline results from the Phase 3 MANIFEST-2 study investigating pelabresib in combination with the JAK inhibitor ruxolitinib compared with placebo plus ruxolitinib in JAK inhibitor-naïve patients with myelofibrosis.

MOR Price Action: MorphoSys shares are down 3.38% at $17.43 at publication Monday.

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