Cancer survival might depend on what time of day you get your treatment, a new study says.

Lung cancer patients who received IV immunotherapy doses earlier in the day tended to live longer, according to results published online Dec. 8 in the journal Cancer.

Getting immunotherapy drugs before 3 p.m. was associated with a 52% lower risk of cancer progression and a 63% lower risk of death, the study found.

This could be an inexpensive way to extend survival for cancer patients, said senior researcher Dr. Yongchang Zhang, an associate professor at the Affiliated Cancer Hospital of Xiangya School of Medicine at Central South University in China.

“Adjusting infusion timing is a straightforward and easily implementable intervention that can be adopted across diverse health care settings without additional cost,” Zhang said in a news release.

For the new study, researchers tracked nearly 400 people with advanced small cell lung cancer who’d been prescribed the immunotherapy drugs atezolizumab or durvalumab alongside standard chemotherapy. The patients were treated between May 2019 and October 2023.

Both immunotherapy drugs work by blocking cancer cells’ ability to evade detection by the immune system, according to Drugs.com.

Results showed that people who got these IV meds before 3 p.m. experienced significantly longer remission before their cancer again began to spread. They also had significantly better survival.

“This study has immediate clinical applicability and the potential to transform current treatment protocols for small cell lung cancer,” Zhang said.

The effect is likely due to people’s circadian rhythms — the internal clock that affects different body processes, including immune reactions, researchers said.

However, more research is needed to understand the effect of circadian rhythms on cancer therapies and how to best leverage a person’s internal clock to maximize treatment benefits, researchers said.

“These findings suggest a critical interplay between biological rhythms and tumor immunotherapy, offering novel opportunities for optimizing treatment strategies,” researchers concluded.