Detecting Metastatic Patterns of Oligometastatic Breast Cancer: A Comparative Analysis of 18 F-FDG PET/CT and Conventional CT Imaging

Metastasis-directed therapy has the potential to improve progression-free and overall survival in oligometastatic disease (OMD). For breast cancer, however, randomized trials have failed so far to confirm this finding. Because the concept of metastasis-directed therapy in OMD is highly dependent on the accuracy of the imaging modality, we aimed to assess the impact of F-FDG PET/CT on the definition of OMD in breast cancer patients. Eighty patients with a total of 150 F-FDG PET/CT images (between October 2006 and January 2022) were enrolled in this retrospective study at the Technical University of Munich. The inclusion criteria were OMD, defined as 1-5 distant metastases, at the time of F-FDG PET/CT. For the current study, we systemically compared the metastatic pattern on F-FDG PET/CT with conventional CT. At the time of F-FDG PET/CT, 21.3% of patients ( = 32) had a first-time diagnosis of metastatic disease, 40.7% ( = 61) had a previous history of OMD, and 38% ( = 57) had a previous history of polymetastatic disease. In 45.3% of cases, the imaging modality ( F-FDG PET/CT vs. conventional CT) had an impact on the assessment of whether OMD was present. An identical metastatic pattern was observed in only 32% of cases. F-FDG PET/CT detected additional metastases in 33.3% of cases, mostly in the nonregional lymph node system. The use of F-FDG PET/CT had a substantial impact on the definition of OMD and detection of metastatic pattern in breast cancer. Our results emphasize the importance of establishing a standardized definition for imaging modalities in future trials and clinical practices related to metastasis-directed therapy in breast cancer patients.