18F-FDG PET/CT of Oligometastatic Disease in Locally Advanced Breast Cancer: PETABC Trial Post Hoc Analysis

Background The optimal treatment of patients with oligometastatic breast cancer and the methods for selecting individuals who may benefit from metastasis-directed therapies are controversial. Purpose To determine the prevalence of oligometastatic disease (OMD; defined as five or fewer distant metastases) in patients with locally advanced breast cancer initially staged at fluorine 18 (¹⁸F) fluorodeoxyglucose (FDG) PET/CT or at CT and bone scintigraphy (CTBS), and to compare patterns of local-regional and distant metastatic disease. Materials and Methods This is a post hoc analysis of data from a prospective, multicenter randomized trial including participants with stage IIb (T3N0) or III invasive ductal carcinoma in the breast between December 2016 and April 2022. Participants were randomized for staging at ¹⁸F-FDG PET/CT or at conventional chest, abdomen, and pelvis CTBS. The prevalence of OMD, sites of distant metastases, and extent of local-regional disease were compared using the χ² test or Fisher exact test. Logistic regression was used to assess the association between imaging and disease extent, with P < .05 indicating a statistically significant difference. Results The study included 369 participants (mean age, 53 years ± 13 [SD]). OMD was more common on ¹⁸F-FDG PET/CT scans (19 of 180; 11%; 95% CI: 6.9, 15.9) than on CTBS scans (eight of 185; 4%; 95% CI: 2.2, 8.3; P = .03). Polymetastatic disease (more than five distant metastases) was also more common on ¹⁸F-FDG PET/CT scans (24 of 180; 13%) than on CTBS scans (13 of 185; 7%; P = .04). Patients with OMD that was depicted on ¹⁸F-FDG PET/CT and CTBS scans had axillary lymph node metastases, but ¹⁸F-FDG PET/CT helped to detect extra-axillary regional lymphadenopathy, extra-regional lymph node metastases, and liver metastases more frequently than did CTBS (six of 19 [32%] vs one of eight [13%], three of 19 [16%] vs 0 of eight [0%], and six of 19 [32%] vs one of eight [13%], respectively; P = .63, .53, and .63, respectively). Conclusion At patient presentation, ¹⁸F-FDG PET/CT helped to detect OMD in more than one in 10 participants with locally advanced breast cancer, which was more than 2.5 times more often than CTBS, and ¹⁸F-FDG PET/CT helped to detect more extensive local-regional metastatic disease. ClinicalTrials.gov Identifier: NCT02751710 © RSNA, 2025 Supplemental material is available for this article. See also the editorial by Ulaner in this issue.