Millions of Americans take antidepressants, and the most common are selective serotonin reuptake inhibitors, or SSRIs. They work by blocking a protein called the serotonin transporter, or SERT, which contributes to serotonin reuptake. This raises serotonin levels. While serotonin helps improve happiness, it also plays a role in our immune systems, and a new study shows SSRIs could be an effective immunotherapy treatment for cancer.

UCLA researchers recently investigated whether SSRIs’ targeting of SERT can increase the ability of our immune system’s T cells to attack tumors. According to the findings, published in the journal Cell, SSRIs helped suppress tumor growth and improve T cells’ antitumor effectiveness in mouse models, as well as in human cancer models for multiple types of cancer, including breast, prostate, and colon.

Dr. Lili Yang, the study’s senior author and professor of microbiology, immunology, and molecular genetics at UCLA, says, “SSRIs made the killer T cells happier in the otherwise oppressive tumor environment by increasing their access to serotonin signals, reinvigorating them to fight and kill cancer cells.”

SSRIs’ efforts were found to help reduce average tumor size by more than 50%, in addition to their T cell effectiveness boost. The team also found that combining SSRIs with another immunotherapy treatment was even more effective. When paired with the immune checkpoint blockade therapy anti-PD-1 antibody, mouse models of melanoma and colon cancer demonstrated reduced tumor size and even had remission in some cases.

The team says immune checkpoint blockades work in fewer than 25% of patients, so this provides a promising avenue to increase the number of patients who can benefit from this therapy.

With the number of people on SSRIs, the findings also pave the way for simple further study.

Dr. Yang explains, “Since around 20% of cancer patients take antidepressants — most commonly SSRIs — we see a unique opportunity to explore how these drugs might improve cancer outcomes. Our goal is to design a clinical trial to compare treatment outcomes between cancer patients who take these medications and those who do not.”

You can read the whole study here. To contribute to more life-changing cancer research, click here!