Prognostic impact of bone metastatic volume beyond vertebrae and pelvis in patients with metastatic hormone-sensitive prostate cancer.

Although bone metastasis beyond the vertebrae and pelvis has been a key factor in prognostic models of metastatic hormone-sensitive prostate cancer (mHSPC), the clinical significance of it is still unclear. The present study evaluated the prognostic impact of the volume of bone metastasis beyond the vertebrae and pelvis on the outcomes of mHSPC and created an ideal risk classification based on it. We retrospectively reviewed 197 patients with mHSPC who were treated with combined androgen blockade as the initial treatment between June 2003 and October 2019. We calculated the bone scan index (BSI), including the BSI beyond the vertebrae and pelvis (bBSI), using BONENAVI, and investigated the association between the BSI and the overall survival (OS) of mHSPC. According to the CHAARTED criteria, 91 and 106 patients were classified into the low- and high-volume groups, respectively. Of the 79 patients who did not have visceral metastasis in the high-volume group, those with a bBSI ≤ 0.27 (n = 16) showed a favorable OS, as did those in the low-volume group. The modified CHAARTED high-volume group (presence of visceral metastases or 4 bone lesions with a bBSI > 0.27) showed a significantly shorter OS than others, with a hazard ratio (HR) of 4.69 (p < 0.001), which was higher than that observed with the original CHAARTED criteria (HR = 4.33). Our data suggested that considering the volume of bone metastasis beyond the vertebrae and pelvis may help to improve the accuracy of risk classification. Further large-scale prospective studies are needed to validate our findings.