GlaxoSmithKline (GSK) and Denmark-based Genmab received some good news with the US Food and Drug Administration's (FDA) approval?for Arzerra (ofatumumab), a monoclonal antibody for patients with chronic lymphocytic leukemia (CLL), a slowly progressing cancer of the blood and bone marrow.?

Arzerra is approved for cancer patients who are no longer responding to the current available treatment options using fludarabine and alemtuzumab. Following the approval, Genmab has become eligible to receive a milestone payment of DKK 116 million (approximately $23 million) from Glaxo.?

Earlier, in May 2009, Arzerra had received a positive recommendation from the FDA's Oncologic Drugs Advisory Committee (ODAC) in which the panel had voted 10-3 in favor of the drug. They had found that Arzerra provided some clinical benefit to patients with CLL whose disease was refractory to fludarabine and alemtuzumab.?

Arzerra has been approved by the FDA under the accelerated approval process to meet the unmet medical need of CLL patients. This type of approval requires a further study of the drug to ensure its effectiveness. Currently, GlaxoSmithKline is conducting a clinical trial in CLL patients to confirm that the addition of Arzerra to standard chemotherapy delays the progression of the disease.?

While Arzerra's effectiveness was evaluated in 59 patients with CLL whose disease no longer responded to the available therapies, the drug's safety was studied in a total of 181 patients. Following the studies, it was found that 42% of patients with CLL who were refractory to both fludarabine and alemtuzumab responded to treatment with Arzerra. These patients had a median duration of response of 6.5 months.?

Common side effects included a decrease in normal white blood cells, pneumonia, fever, cough, diarrhea, lower red blood cell counts and fatigue among others. However, we remain concerned about the most serious side effect, an increased risk of infectios including progressive multifocal leukoencephalopathy (PML), a brain infection that is generally fatal. Tysabri, a multiple sclerosis drug co-developed by Biogen Idec (BIIB) and Elan Pharmaceuticals (ELN) is also under the regulatory scanner related to the occurrence of PML in patients taking the drug over a prolonged time period.?

Although Arzerra has good sales potential, its prospects will be hampered if cases of PML increase in due course.