Safety Concerns with MorphoSys’ Blood Cancer Drug Could Mar $2.9B Novartis Buy: STAT

Bone marrow_iStock, Artur Plawgo

Pictured: 3D illustration of blood cells developing in the bone marrow/iStock, Artur Plawgo

MorphoSys has run into safety problems with its investigational myelofibrosis drug pelabresib, which could potentially complicate the biotech’s $2.9 billion acquisition deal with Novartis, according to STAT News.

Citing anonymous investigators involved with pelabresib’s Phase III study, STAT reported that there have been “multiple cases” of patients who “rapidly progressed” from myelofibrosis to the more aggressive acute myeloid leukemia (AML) following treatment with pelabresib.

Of the 212 patients in the pelabresib arm in the Phase III study, six patients have progressed to AML compared to only two among the control group, STAT reported. MorphoSys has already informed the FDA about these safety signals and the regulator is monitoring the situation and has since warned physicians involved in the study.

A MorphoSys spokesperson told BioSpace in an emailed statement that the company remains “confident in the benefit-risk profile of the pelabresib and ruxolitinib combination.”

“The proposed acquisition by Novartis is advancing steadily, and we continue to anticipate its closure in the first half of 2024,” the spokesperson continued, adding that the company does not publicly disclose details of its interactions with regulatory authorities “as a practice.”

A Novartis spokesperson told BioSpace that its “proposed agreement to acquire MorphoSys has not yet closed and we are unable to comment at this time.”

Pelabresib is an investigational small molecule blocker of BET proteins, which have been shown to play a role in pro-inflammatory pathways and in the production of abnormal blood cell precursors called megakaryocytes, according to MorphySys’ website. A regulatory submission for the drug candidate is scheduled for the second half of 2024.

Pelabresib’s promise contributed heavily to the $2.9 billion acquisition agreement between Novartis and MorphoSys in February 2024. Earlier this month, Novartis announced that it had commenced the tender offer for MorphoSys. It remains unclear if the emerging safety signals of pelabresib will imperil the acquisition.

In November 2023, MorphoSys posted mixed Phase III findings for pelabresib, showing that the drug failed to hit one of its two key endpoints. When used with Jakafi (ruxolitinib), pelabresib was able to induce a statistically significant and clinically meaningful improvement in the percentage of patients that saw at least a 35% drop in spleen volume at 24 weeks.

At the same time, the drug combo was unable to significantly improve total symptom score.

These mixed results roused concerns among some executives in Novartis, STAT reported in February 2024, citing two separate anonymous sources. The $2.9 billion deal allows Novartis to drop out of the acquisition in case the FDA rejects MorphoSys’ bid to file an application for pelabresib.

MorphoSys is scheduled to present new Phase III efficacy and safety data for pelabresib at the upcoming annual meeting of the American Society of Clinical Oncology, taking place in Chicago from May 31 through June 4, 2024.

Tristan Manalac is an independent science writer based in Metro Manila, Philippines. Reach out to him on LinkedIn or email him at or

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