Chemotherapy and targeted therapies work directly on tumor cells, and if the tumor continues to grow after treatment, doctors will consider stopping the drug and choosing another treatment. But PD-1/PD-L1 inhibitors are unique in that they do not act directly on tumor cells, but rather attack them by “recruiting” (collecting tumor-specific lymphocytes) in the body. “In patients with solid tumors, PD-1/PD-L1 inhibitors usually work within 2-4 months, but they can also take up to 6 months or even a year to work (delayed remission). During the time before it works, the tumor may grow, but after the PD-1/PD-L1 inhibitor works, the tumor shrinks, a phenomenon also known as pseudoprogression.
In these cases, it is not appropriate to stop the drug hastily. So what are the circumstances in which tumor enlargement should be discontinued? The current recommendation for patients on PD-1/PD-L1 inhibitors is to have imaging every 6 to 12 weeks, and if the tumor is enlarging at the first exam, you do not need to discontinue the drug. However, if two consecutive exams are suggestive of tumor enlargement, the physician needs to evaluate this together with the total tumor load, and if the evaluation concludes that treatment is not working, the drug should be discontinued.
Co-reviewed by: Guangdong Provincial People’s Hospital Guangdong Provincial Lung Cancer Institute Dr. Wang Zhen, Deputy Chief Physician Sun Hao