Site-Specific Patterns of Distant Relapse on ^18F-FDG PET/Contrast-Enhanced CT According to Molecular Subtype in Breast Cancer: A Retrospective Cohort Study

PurposeTo describe the site-specific distribution of distant relapse detected by integrated 18F-FDG PET/contrast-enhanced CT (PET/ceCT) in breast cancer patients and to explore its association with molecular subtype and clinicopathological features.MethodsThis retrospective study included 177 postoperative breast cancer patients who underwent PET/ceCT during follow-up/restaging for suspected recurrence. Clinical and pathological data were extracted from a manually curated institutional database, including type of surgery, pathological T stage, pathological nodal status, histology, molecular subtype, PET/ceCT date, and PET/ceCT-detected site of relapse. Site-specific analyses were performed in patients with codable distant relapse.ResultsA PET/ceCT relapse-site entry was available in 141/177 patients (79.7%), and 137/177 (77.4%) had codable distant relapse. Molecular subtype was available in 166/177 patients (93.8%). Bone was the most frequent site of distant relapse (81/137, 59.1%), followed by lung (44/137, 32.1%), distant lymph nodes (41/137, 29.9%), and liver (40/137, 29.2%); brain involvement was uncommon (8/137, 5.8%). Single-site and multisite relapse were observed in 70/137 (51.1%) and 67/137 (48.9%) patients, respectively. Bone involvement was significantly more frequent in luminal than in non-luminal tumors (65/101, 64.4% vs 11/29, 37.9%; p=0.018).ConclusionPET/ceCT disclosed non-random and biologically meaningful patterns of distant relapse in breast cancer. Bone-dominant relapse was the prevailing phenotype overall and was significantly associated with luminal disease, whereas non-luminal tumors showed relatively more visceral and multisite dissemination