Updated

U.S. regulators have approved an experimental treatment from Johnson & Johnson that may offer hope to multiple myeloma patients who have run out of other options against the blood cancer.

The U.S. Food and Drug Administration on Monday said it had approved Darzalex (daratumumab) for patients who had already undergone at least three prior standard treatments for the cancer, which affects infection-fighting plasma cells that reside in the bone marrow.

Darzalex, given as an infusion, is a monoclonal antibody that works by helping the immune system attack cancer cells. J&J licensed worldwide rights to the medicine from Danish biotech company Genmab A/S.

In one 106-patient study, tumors shrank or were no longer detectable in 29 percent of patients taking Darzalex, and the benefit lasted for an average of 7.4 months. In a second trial, involving 42 patients, 36 percent of patients taking the J&J/Genmab drug saw a partial or complete reduction in tumors.

Researchers said it is the first antibody drug to demonstrate effectiveness against myeloma without having to be combined with other medicines.

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The most common side effects of the treatment included fatigue, nausea, back pain, fever and cough.

An estimated 26,850 Americans are expected to be diagnosed with multiple myeloma in 2015.

All patients eventually become resistant to existing therapies, which include Takeda's Velcade and Celgene's Revlimid, as well as newer drugs Kyprolis from Amgen and Celgene's Pomalyst.