US regulators have agreed to undertake a speedy review of Pfizer's experimental drug inotuzumab ozogamicin as a treatment for adult patients with relapsed or refractory B-cell precursor acute lymphoblastic leukemia (ALL).

Inotuzumab is comprised of a monoclonal antibody targeting CD22, a cell surface antigen expressed on around 90 percent of B-cell malignancies, linked to a cytotoxic agent. When the drug binds to CD22 on malignant B-cells it is taken into the cell, where the cytotoxic agent calicheamicin is released to destroy it.

ALL is an aggressive type of leukaemia with high unmet need and a poor prognosis. The current standard treatment is intensive, long-term chemotherapy, but advancing therapies "is crucial as only 10 percent of adults with ALL who relapse after first-line therapy survive five years or more with current treatment options," Mace Rothenberg, chief medical officer for Pfizer Oncology, has previously noted.

Inotuzumab was awarded breakthrough designation in October 2015 on the back of data from the Phase III INO-VATE trial, which compared the drug to standard of care chemotherapy in 326 adult patients with relapsed or refractory CD22-positive ALL, and showed that it more than doubled complete remission rates.

The co-primary endpoint of complete remission with incomplete haematologic recovery was achieved by 80.7 percent of patients treated with Pfizer's drug and 33.3 percent of those given the standard of care.

"ALL that has recurred after, or is refractory to, first-line therapy is a rapidly progressing and deadly disease," Rothenberg added. "Based on the positive results of the INO-VATE 1022 Phase III trial, we believe inotuzumab ozogamicin, if approved, represents a new treatment option for adult patients with relapsed or refractory B-cell precursor ALL."

A decision by the US Food and Administration is expected in August this year. Inotuzumab ozogamicin is also currently under review in Europe.