496 Background: Approximately 10% of patients with renal cell carcinoma (RCC) have an associated venous tumor thrombus (VTT), the presence of which impacts surgical management and increases perioperative risk. Historical systemic therapy regimens had limited success in downsizing VTT; however, the impact of immune checkpoint inhibitors (ICIs) on VTT shrinkage is unknown. Our primary objective is to assess VTT shrinkage comparing responses to ICI versus non-ICI regimens. Methods: This multicenter retrospective cohort study included patients with RCC and VTT from 2006-2024 who received upfront systemic therapy. Patients were evaluated at tertiary referral centers across Mayo Clinic Rochester, Florida, and Arizona. Systemic therapies were categorized as ICI versus non-ICI regimens. VTT length was quantified by distance relative to the superior border of the renal vein ostium. The primary outcome was change in VTT length on serial imaging as measured by absolute length reduction (cm), RECIST version 1.1 criteria, and Mayo VTT level reclassification. Linear mixed-effect models (LMMs) identified associations with VTT shrinkage and clinicopathologic features. Results: A total of 108 patients with median age 65 years (IQR 57-71) were included, of whom 49 (45%) received ICI regimens. ICI regimens were associated with greater VTT shrinkage (1cm vs 0.1 cm, p=0.025), increased RECIST responses (51% vs 32%, p=0.046), and a higher rate downstaging per Mayo VTT level (33% vs 12%, p=0.008) compared to non-ICI regimens. On multivariable LMM analysis, ICI regimens remained more likely to result in VTT shrinkage compared to non-ICI regimens (-0.12 cm/month, 95% CI –0.24-0.00, p=0.046). Absence of abdominal lymphadenopathy was also associated with VTT shrinkage (-0.18cm/month, 95% CI -0.06- -0.30, p=0.004). Initial Mayo VTT level, IMDC risk, and number of metastatic sites were not associated with VTT shrinkage. Conclusions: Treatment with ICI-regimens resulted in VTT shrinkage and Mayo VTT level reduction. This is a particularly important area of exploration as radical nephrectomy and tumor thrombectomy carry up to a 40% risk of peri-operative major complications. These data support using ICI regimens for patients with RCC with VTT who are not candidates for upfront surgery and prioritizing ICI regimens in neoadjuvant clinical trials.
Li et al. (Sun,) studied this question.