Early metabolic response assessment of breast cancer liver metastases: 4-week posttreatment FDG PET predicts survival after 90Y microsphere radioembolization.

Aim To evaluate the feasibility of early metabolic response assessment with (18) F-FDG PET/CT in patients with breast cancer liver metastases 4 weeks after radioembolization with Yttrium-90 labeled microspheres. Methods 25 patients (mean age 58y, range 40-74) with advanced stage liver metastases of breast cancer were treated with 1.9 +/- 0.4 GBq of 90Y-microspheres in the salvage setting and underwent (18) F-FDG PET/CT at baseline and 4 weeks post-radioembolization. 14 patients (56 %) had an excessive hepatic tumor burden (> 50 % of total liver volume), 21 patients (84 %) had extrahepatic disease. Liver lesions with the highest SUV (max) were selected as target lesions and a cut-off was set at 50 % reduction to separate responders from non-responders. The predictive impact of metabolic response on overall survival (OS) was investigated along with other prognostic factors. Results The median OS in this highly advanced metastatic cohort was 7 months (95 % CI, 5-9). All patients had a reduction in SUV (max) (mean Delta SUV (max) : -49 +/- 26 %) at 4 weeks post-treatment. Patients with > 50 % SUV (max) reduction survived longer (median OS 13 mo, 95 % CI 8-18) than the remaining patients (median OS 4 mo, 95 % CI 2-6; p = 0.001). From all investigated baseline factors including age, performance status, and presence of extra-hepatic disease, only the hepatic tumor burden had a significant impact on OS (p = 0.02). Conclusions This is the first preliminary evidence in breast cancer that early post-radioembolization molecular response assessment of treated liver metastases - as early as 4 weeks posttreatment - may predict survival. If confirmed by larger series, FDG PET/CT could be considered for early response-adapted treatment modifications.