The Effects of Adding Palbociclib to Endocrine Therapy to Treat Advanced Breast Cancer: A Plain Language Summary of a Study Using the PALOMA-2 and PALOMA-3 Trial Results

What is this summary about? This is a summary of an article that reported results of a study using data from two phase 3 clinical trials called “PALOMA-2” and “PALOMA-3.” Both PALOMA-2 and PALOMA-3 trials included women with HR+/HER2− advanced breast cancer. HR+/HER2− breast cancer means the breast cancer cells of these women have receptors for female sex hormones and little or no HER2 receptors. Both PALOMA trials tested the effect of adding a medication called palbociclib (brand name, Ibrance®) to a hormone therapy. Hormone therapy, also known as endocrine therapy, is a treatment that blocks or removes hormones that cause cancer cells to grow and divide. In both trials, women took endocrine therapy with either palbociclib or a placebo. What was the aim of this study? The researchers aimed to see if the results from the PALOMA trials were similar for subgroups of women in the 2 trials. The subgroups in the study included women who shared certain features about their cancer or treatment history, for example, women whose cancer had spread to the liver. For each subgroup, the study compared the results from the 2 treatment groups: (1) women who took palbociclib plus endocrine therapy, and (2) women who took placebo plus endocrine therapy. What were the results & what do they mean? The same effect was found in all subgroups. Compared with those who took placebo, women who took palbociclib lived longer without their cancer getting worse (growing or spreading). Also, among women who had chemotherapy after stopping the trial treatment, those who took palbociclib started chemotherapy later than those who took placebo. Because palbociclib slows cancer growth and leads to tumor shrinkage, this may have played a part in starting chemotherapy later. These results show that palbociclib plus endocrine therapy is better at slowing the progression of advanced HR+/HER2− breast cancer than endocrine therapy alone. This can be said for women with different advanced HR+/HER2− breast cancer features and treatment history. Overall, the results support women taking palbociclib with an endocrine therapy if they have advanced HR+/HER2− breast cancer.