Combined PET/CT scanning: melanoma patients’ response to ICI therapy could be identified


A new study published in The Journal of Nuclear Medicine reported that advanced melanoma could be diagnosed by immune checkpoint inhibitor (ICI) therapy in individual patients. The research revealed that combination of positron emission tomography/computed tomography (PET/CT) scanning initially could determine the benefits of treatment in patients with advanced melanoma. Because of prospective serious side-effects, the initial determination of ineffectiveness of ICI therapy could avoid unnecessary risk exposure. Thus, different treatments could be chosen. 

T cells and some cancer cells produce specific proteins that inhibit T cells to destroy the cancer cells. Immune checkpoint inhibitors (ICI) block those checkpoint proteins and thus enhance the ability of T cells to kill tumor cells.

Steve Y. Cho, the study author, describes, “Determining response to ICI therapy has been challenging. Current anatomic CT-based response criteria are typically performed at the earliest two to four months into treatment and are limited in their ability to assess stable disease and pseudoprogression.”

The researchers used 18F-fluorodeoxyglucose-(FDG)-PET/CT scanning as an early predictor to determine response to ICI therapy in people (n=20) with advanced melanoma. Every patient had three scans: before treatment, at 21 to 28 days and four months. Criteria developed by scientists to predict future response to ICI with 100% sensitivity, 93% specificity, and 95% accuracy.

Cho added that the scientists distinguished ultimate clinical benefit more precisely by combining 18F-FDG PET-based response criteria and CT-based criteria. By outcomes, they proposed a combined PET and CT-based response criteria to ICI therapy in advanced melanoma. The researchers found a small increase in 18F-FDG tumor uptake at the early time point that involved an active immune-mediated 'flare' which showed the response of a tumor to the immune therapy.

He cautions, “While immune therapies, including the particular class of immune checkpoint inhibitors used in this study, promise new hope for durable tumor responses and remission for a variety of cancers, they are not without a cost.” The immune cells which kill cancer cells could also destroy healthy cells that results in immune-associated adverse events. Hence the constant use of ICI therapies was restricted, which decreased the risk of side effects and provided the option of a different treatment. Future study would involve a large number of patients, he added.

Cho concluded that new emerging immune-based treatments in drug development for melanoma and other cancers could be evaluated by using a combination of more efficient and early PET- and CT-based response criteria.

Combining functional and anatomic imaging parameters from 18F-FDG PET/CT scans performed early in ICI appears predictive for eventual response in patients with advanced melanoma. These findings require validation in larger cohorts.