Prognostic factors in patients with bone metastasis of renal cell carcinoma in the era of immune checkpoint inhibitors.

[BACKGROUND] Patients with clear cell renal cell carcinoma (ccRCC) have a higher incidence of bone metastasis; however, the availability of immune checkpoint inhibitors (ICIs) is expected to improve their overall survival (OS). Hence, accurate data on the prognosis and survival of patients with bone metastases are necessary to recommend appropriate treatments. Therefore, we investigated the prognosis and prognostic factors of patients with ccRCC bone metastasis in the era of ICIs.

[METHODS] This retrospective cohort study included 33 patients with ccRCC who were treated for bone metastases between 2016 and 2022. We evaluated the association between OS and clinical parameters, including serum biochemical concentrations, and blood cell count, using Kaplan-Meier curves and Cox proportional hazards models.

[RESULTS] The median OS was 28 months (95 % confidence interval (CI): 8 months - not censored), and the 1-year survival rate was 64 %. Twenty-one patients were treated with ICIs after bone metastasis diagnosis. The multivariate analysis revealed that the use of ICIs after bone metastasis diagnosis was a good prognostic factor (hazard ratio, 0.32; 95 % CI: 0.11-0.89, p = 0.029). Patients in the Katagiri score 5-7 points group using ICIs had a significantly longer survival (p = 0.012) but similar OS compared to the 2-4 points group (p = 0.34).

[CONCLUSIONS] ICI use after the diagnosis of bone metastasis may be a favorable prognostic factor in patients with bone metastases due to ccRCC. The predictive power of the current scoring system could underestimate the prognoses in patients with ccRCC and bone metastasis not treated with ICIs, highlighting the need for a better predictive scoring system in the era of ICIs.