New research presented at the 2023 American Society of Clinical Oncology Annual Meeting shows that a drug targeting specific genes that help cancer cells thrive, when combined with hormonal therapy, may help women with a specific kind of early-stage breast cancer. The targeted-therapy drug, ribociclib (Kisqali), was successful for women with hormone-receptor positive/HER2-negative early-stage breast cancer. Patients who received the drug along with standard hormone therapy had longer lengths of time without symptoms after their first cancer treatment, compared to those who only received hormone therapy. Adding the drug to hormone therapy also reduced the risk of their cancer returning by 25%. Hormone receptor-positive/HER2-negative breast cancer is the most common subtype, making up about 65% to 70% of breast cancer cases in the United States.
Ribociclib is a CDK4/6 inhibitor, a drug designed to stop the growth of cancer cells. The FDA has approved it to treat HR-positive, HER2-negative advanced or metastatic breast cancer in premenopausal women along with another drug, called an aromatase inhibitor, that is used to lower estrogen levels, or along with another drug called fulvestrant in postmenopausal women.
The researchers assigned about 5,000 people with stage IIA, IIB, or III HR-positive, HER2-negative breast cancer, who were at risk for their cancer returning, to be treated with ribociclib with hormonal therapy (2,549 patients) or hormonal therapy alone (2,552 patients). Over time, cancer returned for 189 patients in the ribociclib group, compared to 237 using hormonal therapy alone. The patients were followed for about 34 months, with 20% completing 3 years of treatment with ribociclib, and 57% completing 2 years of treatment.
Ribociclib also showed better outcomes in overall survival and length of time without any signs or symptoms of cancer in the long term. Sylvia Adams, MD, a medical oncologist and director of the Breast Cancer Center at New York University Langone Perlmutter Cancer Center, said, “Patients with [this type of cancer] now have a new treatment option. Adding … ribociclib to endocrine therapy after surgery can decrease risk of recurrence and improve survival.”
Dennis Slamon, MD, director of clinical and translational research at the UCLA Comprehensive Cancer Center, who presented the findings at the meeting, explained that longer follow-up is needed to see if ribociclib will make a difference in overall survival. There is another CDK4/6 inhibitor, abemaciclib, that is FDA-approved for use along with hormonal therapy. “Now we will have a second option, once ribociclib is approved for this indication, and can decide with patients which one of these two drugs to use based on their side effect profiles and/or treatment duration,” said Adams.