Multiplexed P21/MCM-2 Detection Predicts Relapse and May Identify Tyrosine Kinase Inhibitor–Resistant Patients in Clear Cell Renal Cell Carcinoma

Current clinical tools for predicting relapse and guiding adjuvant therapy in clear cell renal cell carcinoma (ccRCC) lack precision, especially in intermediate-risk disease. This study evaluated whether a nonproliferative tumor cell phenotype, P21 (CDKN1A inhibitor)-positive and MCM2 (DNA replication protein)-negative (P21+/MCM2-), could serve as a robust biomarker to improve prognostic stratification and guide postnephrectomy treatment decisions. We used multiplex immunofluorescence and Artificial Intelligence-based image analysis on nephrectomy specimens from three independent ccRCC cohorts: UK arm of the SORCE trial (n = 382), Korean (n = 71), and Scottish (n = 88). An optimal 2% cutoff for P21+/MCM2- cells was determined using X-tile software. Additional analyses assessed endoglin/CD105 coexpression, paired primary-metastatic samples (n = 41), and associations with adjuvant sorafenib therapy. In two intermediate-risk ccRCC cohorts (SORCE, n = 63; Korean, n = 71), patients with >2% P21+/MCM2- cells had significantly longer time to relapse [HR = 0.17; 95% confidence interval (CI), 0.06-0.54; HR = 0.27; 95% CI, 0.10-0.72]. Prognostic value was confirmed in high-risk (SORCE, HR = 0.43; 95% CI, 0.19-0.99) and all-risk (Scottish, HR = 0.37; 95% CI, 0.14-0.98) cohorts. Notably, patients with high P21+/MCM2- levels on placebo fared better than those receiving adjuvant TKI therapy (HR = 0.29; 95% CI, 0.16-0.50). In 41 paired samples, 85% showed higher P21+/MCM2- abundance in metastases than in primary tumors. As a conclusion, P21+/MCM2- cell count is a robust biomarker that refines relapse risk stratification in ccRCC and identifies patients who may not benefit from adjuvant tyrosine kinase inhibitor (TKI) therapy. High levels of these nonproliferative, senescent-like cells suggest tumor dormancy and a more favorable outcome without treatment. SIGNIFICANCE: After surgery for clear cell renal cell carcinoma, relapse risk and benefit from adjuvant therapy remain uncertain. We identify a distinct P21+/MCM2- tumor phenotype, nonproliferative and senescent-like, linked to favorable outcomes. Across three cohorts, >2% of these cells reduced relapse risk, but benefit was lost with adjuvant TKIs.