Reassessing the Racial Survival Disparity in Renal Medullary Carcinoma: The Roles of Race-Ethnicity Misclassification...

Renal medullary carcinoma (RMC) is a rare, aggressive kidney cancer affecting young Black patients. A previous analysis of the Surveillance, Epidemiology and End Results (SEER) database reported an approximately five-fold higher mortality among Black patients. We reassessed whether this disparity is reproducible and examined the roles of race-ethnicity misclassification and access to surgery.

We identified RMC cases (histology code 8510/3) in the SEER database (2000-2022). Overall survival was modelled with multivariable Cox regression and cancer-specific survival with Fine-Gray competing-risks regression. The SEER race code was reclassified into the National Institutes of Health five-class race-ethnicity scheme, and access to surgery was examined with inverse-probability-of-treatment weighting. Robustness was assessed across six analytic approaches and a leave-one-cell-out diagnostic.

Of 148 patients, 147 were analysed (median age 27 years; 79% Black; median overall survival 9 months). The five-fold difference was not reproduced: the adjusted hazard ratio (HR) for Black versus White race was 1.17 (95% confidence interval [CI] 0.71-1.93) and the Fine-Gray subdistribution HR was 1.01 (0.58-1.76), with every CI spanning 1.0. Of 29 patients coded 'White', 17 (59%) were Hispanic and only 12 were non-Hispanic White. An apparent sex×race interaction collapsed when any single cell was removed (P = 1.0). Surgery was associated with longer survival, but this apparent benefit is likely confounded by indication and should not be interpreted as causal.

The previously reported racial disparity in RMC was not reproducible and is better explained by race-ethnicity misclassification and access to treatment than by tumour biology. These findings caution against crude Black-White comparisons in small registry cohorts.