New research suggests that estrogen plays a role in allowing hormone receptor-negative breast cancer to grow. This is because estrogen limits the ability of the immune system to attack cancer cells; it also makes immunotherapy medicines, like Keytruda (chemical name: pembrolizumab), less effective. Dr. Donald McDonnell, senior author of the study, explains the results and how they might make a difference for people with breast cancer.

Listen to the episode to hear Dr. McDonnell explain: