Less than five months after a pair of biotech companies submitted a candidate cancer drug to the Food & Drug Administration, the FDA has approved the drug ibrutinib as a "breakthrough therapy" for a rare and deadly form of the cancer, mantle cell lymphoma. The new medication, to be marketed under the commercial name Imbruvica, becomes a new option for patients who are diagnosed with this malignancy of the immune system's B-cells and who have received at least one prior therapy.
Each year, some 2,900 Americans receive a diagnosis of mantle cell lymphoma. Existing treatments rarely halt this aggressive cancer's progression for more than five months. The FDA accelerated its consideration of ibrutinib because mantle cell lymphoma is a life-threatening disease for which few effective treatment options are available.
"MCL is the worst of the worst," said Dr. John Byrd, a hematologist at the Ohio State University Comprehensive Cancer Center, who is leading a trial testing the ibrutinib's effectiveness in a more common but less aggressive form of lymphoma, chronic lymphatic leukemia (CLL), which is diagnosed in roughly 14,000 patients a year. A new drug that shows promise of achieving "very, very durable" results in some patients "is a blessing," said Byrd, who has served as an unpaid consultant to Pharmacyclics.
Trials of the drug's effectiveness in treatment of CLL have also been conducted at City of Hope in Duarte, where hematologist Dr. Leslie Popplewell said, "It's nice to have the more gentle therapy" of a daily pill available to patients whose principal option -- if they are healthy enough to withstand it -- has been a grueling regimen of intravenous chemotherapy with debilitating side effects.
City of Hope will soon open new clinical trials of ibrutinib for patients with untreated low-grade lymphomas, new diagnosed follicular lymphoma and refractory marginal zone lymphoma -- all less aggressive, more chronic forms of the disease.
"I don't think we've explored the full capabilities if ibrutinib," Popplewell said.
Because of its accelerated review, the drug's approval by the FDA was based not on hard outcomes such as patients' survival or symptom improvement, but on trial investigators' assessment of the "overall response rate" of patients taking the drug. In a multi-center clinical trial that did not assign any subjects to take a placebo medication for comparison, 65.8% of 111 patients with mantle cell lymphoma were deemed to have responded to the medication, with 17% of the total achieving a "complete response" and 49% achieving a "partial response."
The median duration of patients' responsiveness to the medication was 17.5 months.
Ibrutinib is expected to be considered next by the FDA as a treatment for chronic lymphatic leukemia, a disease for which second-line treatment has been able to hold off progression for a median of 14 months. Ohio State University's Byrd said that roughly three-quarters of the patients he is overseeing in the trial are still taking the medication and doing well at the 26-month mark.
For nearly half of research subjects who took a high dose of ibrutinib, bleeding events, including bruising, occurred, and they were serious in 5% of those who took it. Infections, renal toxicity and disturbances in blood chemistry all occurred in at least a quarter of subjects taking the medication.