Pfizer announced that its investigational antibody-drug conjugate (ADC) inotuzumab ozogamicin received Breakthrough Therapy designation from the U.S. FDA for acute lymphoblastic leukemia (ALL). Inotuzumab ozogamicin is an ADC comprised of a monoclonal antibody (mAb) targeting CD22, a cell surface antigen expressed on approximately 90 percent of B-cell malignancies, linked to a cytotoxic agent. When inotuzumab ozogamicin binds to the CD22 antigen on malignant B-cells, it is internalized into the cell, where the cytotoxic agent calicheamicin is released to destroy the cell. ALL is an aggressive type of leukemia with high unmet need and a poor prognosis in adults. The current standard treatment is intensive, long-term chemotherapy. In 2015, it is estimated that 6,250 cases of ALL will be diagnosed in the United States.