LAG-3: another brake to release in breast cancer?

Upregulation of inhibitory immune checkpoints is critical for the control of T-cell activation in order to prevent autoimmunity and tissue damage. It is now clear that tumors can hijack immune checkpoint mechanisms as protection against the anticancer T-cell response. Blockade of the PD-1/PD-L1 immune checkpoint pathway has created a revolution in the treatment of melanoma, lung cancer and several other cancer types. In metastatic breast cancer patients, the response rates to PD-1 blocking antibodies are modest (4%–25%), but durable responses are seen [1–7]. Given that the majority of patients do not have clinical benefit, there is an urgent need to improve immunotherapy for breast cancer patients. This optimization is not a paved road and requires the integration of different parallel approaches, such as the search for predictive biomarkers [8], combination treatment with conventional therapies [9, 10], strategies to convert cold tumors into hot tumors [4, 11] and development of novel immunomodulatory compounds.