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Response monitoring in metastatic breast cancer - a prospective study comparing 18F-FDG PET/CT with conventional CT.

PURPOSE: This study aimed to compare contrast-enhanced CT (CE-CT) and 18F-FDG PET/CT for response monitoring in metastatic breast cancer (MBC) using the standardized response evaluation criteria RECIST 1.1 and PERCIST. The objective was to examine whether progressive disease was detected systematically earlier by one of the modalities. METHODS: Women with biopsy-verified MBC were enrolled prospectively and monitored using combined CE-CT and 18F-FDG PET/CT every 9-12 weeks to evaluate response to first-line treatment. CE-CT scans and RECIST 1.1 were used for clinical decision-making without accessing the 18F-FDG PET/CT scans. At study completion, 18F-FDG PET/CT scans were unblinded and assessed according to PERCIST. Visual assessment was used if response criteria could not be applied. The modality-specific time to progression was defined as the time from the baseline scan until the first scan demonstrating progression. Paired comparative analyses for CE-CT vs. 18F-FDG PET/CT were applied, and the primary endpoint was earlier detection of progression by one modality. Secondary endpoints were time to detection of progression, response categorization, visualization of changes in response over time, and measurable disease according to RECIST and PERCIST. RESULTS: In total, 87 women were evaluable with a median of six (1-11) follow-up scans. Progression was detected first by 18F-FDG PET/CT in 43/87 patients (49.4%) and by CE-CT first in 1/87 (1.15%) (P < 0.0001). Excluding patients without progression (n = 32), progression was seen first by 18F-FDG PET/CT in 78.2% (43/55) of patients. The median time from detection of progression by 18F-FDG PET/CT to that of CE-CT was six months (95% CI 4.3-6.4). At baseline, 76 patients (76/87, 87.4%) had measurable disease according to PERCIST and 51 (51/87, 58.6%) according to RECIST 1.1. Moreover, 18F-FDG PET/CT provided an improved visualization of changes in response over time, as seen in the graphical abstract. CONCLUSION: Disease progression was detected earlier by 18F-FDG PET/CT than CE-CT in most patients with a potentially clinically relevant median six-month delay for CE-CT. More patients had measurable disease according to PERCIST compared with RECIST 1.1. The magnitude of the final benefit for patients is a perspective for future research.