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ON CO L OG Y New Treatment Option for Women with Advanced Breast Cancer W omen diagnosed with one of the most common types of breast cancer now have an additional medication to help fight the disease. The U.S. Food and Drug Administration (FDA) recently approved palbociclib (Ibrance) for postmenopausal patients with breast cancer that has spread to other areas of the body. The medication is aimed at women with a type of breast cancer known as estrogen receptor-positive/HER2-negative (ER+/ HER2-). The ER+/HER2- subgroup represents about 60 percent of breast-cancer cases, “so we believe this agent can have a great impact,” says Dennis Slamon, MD, PhD, director of the Revlon/UCLA Women’s Cancer Research Program and Clinical/ Translational Research at UCLA’s Jonsson Comprehensive Cancer Center. The medication represents a new strategy in treating breast cancer. It’s the first in a class of medications that target proteins called cyclin-dependent kinases 4 and 6 (CDK4/6). These proteins allow cancer cells to divide, but palbociclib disrupts them. Researchers have known about these proteins for many years, but it was unclear who might be helped by drugs that disrupted the proteins. In studies that began in 2007, UCLA scientists demonstrated that women with estrogen receptor-positive breast cancer could benefit from drugs that addressed CDK4/6. “Cell division is not well controlled; that’s one of the hallmarks of cancer,” says Richard Finn, MD, of UCLA’s Jonsson Comprehensive Cancer Center. “For many years, people have been trying to target these CDK4/6 receptors. What we have been able to do is identify a type of cancer that might benefit from CDK4/6 inhibition.” Palbociclib is used in combination with letrozole, a medication used to treat this type of breast cancer in postmenopausal women. In the clinical trial, participants treated with palbociclib plus letrozole lived about 20 months without their disease progressing, compared to about 10 months in participants receiving only letrozole. More than 80 percent of the patients in the study received some benefit from this treatment. In April 2013, the FDA granted the drug “breakthrough therapy” status, allowing it to be fast-tracked to early approval. “I believe palbociclib will now become a standard treatment approach for postmenopausal women with ER+/HER2- metastatic breast cancer,” Dr. Slamon says. The drug did cause a decrease in infection- fighting white blood cells. But that side effect is manageable, Dr. Finn says. “So much cancer research is just hit and miss. You do a study and hope to get something,” he says. “This clinical study was based on a very strong scientific rationale. It wasn’t random. That is why we saw positive results. This type of result is not often seen in cancer medicine.” CDK4/6 medications are under investigation for other types of cancers, Dr. Finn says. To view a video about treatment options for women with breast cancer, go to: UCLAHEALTH.ORG 1-800-UCLA-MD1 (1-800-825-2631)