Impact of number of bone metastases on cancer control outcomes in mHSPC, independent of the axial-skeleton CHAARTED definition.

OBJECTIVE: Patient and treatment stratification for metastatic hormone-sensitive prostate cancer (mHSPC) is usually based on metastatic burden according to CHAARTED criteria, classifying high-volume disease as at least 4 bone metastases, one outside the axial skeleton, or one visceral metastasis. We aimed to examine the impact of the number of bone metastases independently of CHAARTED criteria. MATERIAL AND METHODS: Using the FRAMCAP (FRAnkfurt Metastatic Cancer database of the Prostate), time to castration resistant prostate cancer (ttCRPC) and overall survival (OS) were analyzed in patients with mHSPC stratified into 1 to 3 vs. 4 to 7 vs. ≥8 bone metastases, irrespective of axial skeletal location. Comparisons were made against CHAARTED low- and high-volume mHSPC outcomes. RESULTS: Of 398 patients with mHSPC, 43% harbored 1 to 3, 19% 4 to 7 and 38% ≥8 bone metastases. CHAARTED high-volume mHSPC was diagnosed in 52%. Median ttCRPC was lowest for ≥8 bone metastases (16.2 months), followed by 4 to 7 (17.3 months) and 1 to 3 bone metastases (28.4 months; P < 0.01). Similar ttCRPC outcomes were observed when stratification was made into CHAARTED low- (28.4 months) vs. high-volume mHSPC (17.2 months). Median OS was also significantly shorter for ≥8 bone metastases (34.5 months), followed by 4 to 7 (53.3 months), and 1 to 3 (56.4 months; P < 0.001). Comparable OS outcomes were observed in CHAARTED low- (58.3 months) vs. high-volume mHSPC (43.4 months). CONCLUSION: The number of bone metastases, regardless of their localization in the axial skeleton, has a significant influence on cancer-control outcomes. Especially, patients with ≥4 bone metastases have comparable outcomes to CHAARTED high-volume patients with mHSPC with at least one metastasis outside the axial skeleton.