Tyrosine Kinase Inhibitors Outperform Immune Checkpoint Inhibitors in Bone-Predominant Metastatic Renal Cell Carcinoma: A Multicenter Real-World Analysis

<b>Background:</b> Bone-predominant metastatic renal cell carcinoma (mRCC) presents significant clinical challenges due to its associated morbidities and poor prognosis. Optimal first-line treatment remains unclear, largely because these patients are often excluded from clinical trials due to difficulties in measuring bone lesions. Emerging evidence suggests that bone metastases exhibit high angiogenesis gene signatures, potentially predicting favorable responses to tyrosine kinase inhibitors (TKIs). <b>Methods:</b> We conducted a multicenter retrospective analysis of patients with bone-predominant mRCC treated at The Ohio State University Comprehensive Cancer Center and Fred Hutchinson Cancer Center from January 2008 to June 2021. Bone predominance was defined as having a greater number of osseous metastases compared to extra-osseous sites using computed tomography or bone scans. Patients receiving first-line TKIs or immune checkpoint inhibitors (ICIs) were included; those treated with combination TKI-ICI therapies were excluded due to limited numbers. Demographic, clinical, and treatment data were collected. Progression-free survival (PFS) and overall survival (OS) were analyzed using Kaplan-Meier methods and compared using the log-rank test. Univariate Cox regression analysis was conducted to identify factors associated with OS. <b>Results:</b> A total of 69 patients with bone-predominant mRCC were identified, with 40 receiving TKIs and 29 receiving ICIs as first-line therapy. Baseline characteristics were comparable between groups. The median OS was significantly longer for patients treated with TKIs compared to those receiving ICIs (41.3 months vs. 19.3 months; log-rank <i>P</i> = 0.036). A trend toward improved median PFS was observed in the TKI group (7.9 months vs. 4.9 months; <i>P</i> = 0.075). Univariate analysis showed that treatment with ICIs was associated with an increased risk of death compared to TKIs (hazard ratio = 1.96; <i>P</i> = 0.040). Objective response rates were higher in the TKI group (22.9% vs. 12.0%), although this difference was not statistically significant (<i>P</i> = 0.332). <b>Conclusions:</b> In this multicenter real-world analysis, first-line treatment with TKIs was associated with significantly improved OS compared to ICIs in patients with bone-predominant mRCC. These findings suggest that TKI-containing regimens may be the preferred front-line therapy for this patient subgroup. Prospective studies are warranted to validate these results and to optimize treatment strategies for bone-predominant mRCC.