¹⁸F-FDG PET/CT findings and circulating tumor cell counts in the monitoring of systemic therapies for bone metastases from breast cancer

Our objective was to compare the predictive significance of ¹⁸F-FDG PET/CT findings and circulating tumor cell (CTC) count in patients with bone metastases from breast cancer treated with standard systemic therapy. Methods: Breast cancer patients with progressive bone-only metastatic disease without visceral metastases starting a new line of systemic therapy underwent ¹⁸F-FDG PET/CT and had CTC counts determined before and during treatment. Disease status was reassessed by CTC count (≥5 vs. <5 CTC/7.5 mL of blood) and ¹⁸F-FDG PET/CT approximately 2-4 mo after initiation of the new systemic therapy. Results: CTC counts at follow-up agreed with the ¹⁸F-FDG PET/CT assessment in 43 (78%) of the 55 evaluable patients. Of the 12 patients with discordant CTC and ¹⁸F-FDG PET/CT results, 8 (66%) had ≥5 CTCs, with no evidence of progressive disease at the time of the ¹⁸F-FDG PET/CT study, whereas 4 (33%) had <5 CTCs, with evidence of progressive disease by ¹⁸F-FDG PET/CT. ¹⁸F-FDG PET/CT findings and follow-up CTC counts were found to be significantly associated with both progression-free survival (P = 0.02 and P < 0.0001, respectively) and overall survival (P = 0.02 and P = 0.01, respectively). In multivariate analysis, the ¹⁸F-FDG PET/CT assessment remained as the only predictive factor for progression-free survival (P < 0.0001), whereas estrogen receptor status was the only predictive factor for overall survival (P = 0.01). Conclusion: ¹⁸F-FDG PET/CT is a useful tool for therapeutic monitoring in patients with bone metastases from breast cancer. Prospective studies are needed to define the role of ¹⁸F-FDG PET/CT and CTC in the setting of response discordance to establish bone-dominant disease as a tumor-response measurable disease. COPYRIGHT