FDA approves Pfizer's Besponsa in aggressive blood cancer

US regulators have approved Pfizer’s new drug, Besponsa, offering a new option for patients with a rare and aggressive form of blood cancer.

Besponsa (inotuzumab ozogamicin) is the first of its kind to be indicated for adults with relapsed or refractory B-cell precursor acute lymphoblastic leukaemia.

An antibody-drug conjugate, the drug consists of a cancer-targeting antibody attached to a cancer-killing cytotoxic agent, ozogamicin.

The FDA had granted the CD-22 targeting drug a faster six-month priority review after designating it a Breakthrough Therapy, offering an improvement in standard care for a serious disease.

Approval was based on results from the phase 3 INO-VATE ALL trial, a randomised, open-label, international, multi-centre study evaluating the safety and efficacy of Besponsa compared with investigator’s choice of chemotherapy in 326 adult patients with relapsed or refractory B-cell ALL.

The complete remission rate (CR/Cri) for patients treated with Besponsa was 81% compared to 29% with chemotherapy.

A higher proportion of patients treated with Pfizer's drug had only residual amounts of diseased cells in their bloodstreams (minimal residual disease negative, or MRD negative), compared with chemotherapy.

In the Besponsa group, 78% were MRD-negative, while in the chemotherapy group, 28% were MRD-negative.

However Besponsa still did not significantly increase overall survival (OS) compared with chemotherapy – median OS was 7.7 months in patients treated with Besponsa, compared with 6.2 months in the chemotherapy arm.

According to consensus figures from EvaluatePharma, sales forecasts are modest at $347m by 2022, and UCB also has worldwide royalties.

The drug was developed as a collaboration between Pfizer and UK biotech Celltech, which is now part of UCB.

Ozogamicin was also used in Pfizer’s Mylotarg, the first ever antibody-drug conjugate approved in 2000 in acute myeloid leukaemia.

Mylotarg was last year re-approved by the FDA after Pfizer withdrew it from the market in 2010 after post-marketing data failed to confirm its benefit.