FDG uptake reflects breast cancer immunological features: the PD-L1 expression and degree of TILs in primary breast cancer

Background High F18-fluorodeoxyglucose (FDG) uptake has been reported to be a predictor of poor prognosis in patients with breast cancer. We investigated the relationship between FDG uptake and immunological factors, including the data of programmed cell death-ligand 1 (PD-L1), CD8, and tumor-infiltrating lymphocytes (TILs). Methods Breast cancer tissues of 97 patients who underwent surgery without preoperative therapy were examined. The grade of stromal TILs was immunohistochemically evaluated using the criteria of the International TILs Working Group in breast cancer. PD-L1 positivity and CD8 positivity were immunohistochemically evaluated. The FDG uptakes were evaluated based on the standardized uptake value max (SUVmax). The relationships between SUVmax and TIL grade and expression of PD-L1 and CD8 were investigated. Results Among the 97 patients, 41 (42.3%) had a high SUVmax in their primary tumor, based on the SUVmax cut-off value 3 yielded by receiver operating characteristic curves. PD-L1 was positive in 17 patients (17.5%). Our analyses revealed that large tumor size, high nuclear grade, high degree of TILs and positive expression of PD-L1 were significantly associated with high SUVmax in the primary tumor. There were significant associations between SUVmax and the degree of TILs (r = 0.428, p < 0.001) and between SUVmax and the PD-L1 positivity (r = 0.413, p < 0.001). All cases with a high degree of TILs showed high CD8 expression. Conclusion Our results indicate that the FDG uptake may be predictive of immunological features including TILs and PD-L1 expression in breast cancer patients. Additional research is necessary to further evaluate FDG-PET as a biomarker of immune checkpoint therapy in breast cancer.