The role of 18F-FDG PET/CT suvmax values in evaluating treatment response in hormone receptor positive metastatic breast cancer patients receiving CDK4/6 inhibitor therapy

Metastatic breast cancer is a disease with a very poor prognosis. It has been treated with hormonotherapy for years, but due to the promising results of CDK 4/6 inhibitors, combining it with hormonotherapy has taken its place in the treatment. Although there is no standard approach to evaluate the response to CDK 4/6 inhibitors, it may be possible to evaluate it with PET CT. In our study, we aimed to measure the treatment response with PET CT SUVmax value in hormone-positive metastatic breast cancer patients treated with CDK 4/6 inhibitors. Our study was designed as a single-Center retrospective study on 94 patients (93 women, 1 man). The average age at diagnosis of the patients was found to be 55,03. The overall survival time (OSS) of the patients was found to be 169 months, 5-year average overall survival was 77.4%, and 10-year average overall survival was 60.9%. In our study, the most used combination was found to be Ribociclib + Letrozole (45.7%). When looking at the side effect profile associated with CDK 4/6 inhibitors, neutropenia was found to be the most common side effect (35.5% of patients). It was determined that fatigue and nausea were in the second and third places (25.8%, 19.4% respectively). Before starting CDK 4/6 inhibitors, the average of the highest SUVmax value (primary mass + metastasis) was determined as 11,20. It was determined that the average of the highest SUVmax value decreased to 7.32 after treatment started (p = 0.001). It was found that the progression-free survival time was longer in cases with a significant decrease in SUVmax values (AUC: 0.769, p=0.001, cut-off calculated as 3.35) (28,92 months vs. 14.47 months). A significant relationship was found between the difference in the highest SUVmax value before and after treatment with Clinical Benefit Rate (CBR) and Objective Response Rate (ORR) (p = 0.001). We recommend the use of CDK 4/6 inhibitors in addition to hormonal therapy in the treatment of metastatic breast cancer, as they may prevent the progression of the disease.