Response monitoring in metastatic breast cancer: a comparison of survival times between FDG-PET/CT and CE-CT

Introduction: The choice of response monitoring method in metastatic breast cancer (MBC) may impact clinical decision-making and patients’ survival. This study aimed to compare overall survival for patients monitored with contrast-enhanced computed tomography (CE-CT), [¹⁸F]-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT), and a combination of the two methods. Methods: Patients with biopsy-verified MBC treated at Odense University Hospital (Denmark) between 2004-2018, were eligible. Approval was given by the Danish Patient Safety Authority (Ethics permission code: 3-3013-2448/1). Inclusion criteria were: biopsy-verified de novo MBC (primary disseminated and recurrent disease); baseline and at least one follow-up scan for response monitoring; using either FDG-PET/CT, CE-CT, or a combination of the two; standard response monitoring protocol; and regular clinical follow-up. Exclusion criteria were: known other disseminated malignancy, patients with other severe comorbidities at the time of diagnosis, missing data, lost to follow-up due to immigration, and refusal of treatment. Included patients were followed-up until August 2019. Clinical, histopathological, and response monitoring data were analyzed in a multivariable Cox proportional-hazards regression model comparing survival between CE-CT and FDG-PET/CT groups. Results: A total of 300 patients were included in groups of CE-CT (n=144), FDG-PET/CT (n=83), and the combined group (n=73). The study groups were mostly comparable regarding baseline characteristics and the prognostic value of few features with significant differences did not favor a specific study group. Median survival was 30.0 (95% CI: 25.5-36.0), 44.3 (95% CI: 29.7-80.2), and 54.0 (95% CI: 44.3-80.1) months for each group, respectively (Figure 1. Kaplan-Meier plot for survival of metastatic breast cancer patients including risk table underneath plot). Five-year survival rates were comparable for the FDG-PET/CT (41.9%) and the combined groups (43.3%), both of them significantly higher than for the CE-CT group (15.8%). FDG-PET/CT and the combined group had statistically significantly longer survival with hazard ratio (HR) of 0.56 (95% CI: 0.40-0.80, P=0.001) and 0.41 (95% CI: 0.29-0.59, P<0.001), respectively when using the CE-CT group as reference in univariate survival analyses. Adjusted HR for baseline characteristics, was 0.44 (95% CI: 0.28-0.67, P=0.001) for the FDG-PET/CT group when using the CE-CT-group as reference. FDG-PET/CT detected the first progression 4.7 months earlier than CE-CT (9.3 vs. 13.6), which led to an earlier change in treatment. Conclusions: We found prolonged overall survival for patients with metastatic breast cancer when FDG-PET/CT alone or in combination with CE-CT was used for response-monitoring as compared with using CE-CT alone. Our results indicate that using FDG-PET/CT for response monitoring patients with metastatic breast cancer improves clinical decision-making and patients’ survival. Acknowledgements: This study was supported by Centre for Personalized Response Monitoring in Oncology (Odense University Hospital, Denmark) and the University of Southern Denmark.

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