Detecting Metastatic Patterns of Oligometastatic Breast Cancer: A Comparative Analysis of¹⁸F-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 ¹⁸F-FDG PET/CT on the definition of OMD in breast cancer patients. Methods: Eighty patients with a total of 150 ¹⁸F-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 ¹⁸F-FDG PET/CT. For the current study, we systemically compared the metastatic pattern on ¹⁸F-FDG PET/CT with conventional CT. Results: At the time of ¹⁸F-FDG PET/CT, 21.3% of patients (n = 32) had a first-time diagnosis of metastatic disease, 40.7% (n = 61) had a previous history of OMD, and 38% (n = 57) had a previous history of polymetastatic disease. In 45.3% of cases, the imaging modality (¹⁸F-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.¹⁸F-FDG PET/CT detected additional metastases in 33.3% of cases, mostly in the nonregional lymph node system. Conclusion: The use of ¹⁸F-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.