Evaluation of basal and luminal subtypes of urothelial carcinoma in African American and non-African American patients.

Abstract

305 Background: African American (AA) patients with urothelial carcinoma (UC) have been known to have a worse prognosis even when corrected for variables such as tumor stage and grade. Analysis of gene expression of several malignancies has resulted in the discovery of molecular subtypes with well-defined intrinsic biology. Recent studies in high grade (HG), muscle-invasive UC have led to the identification of two intrinsic, molecular subsets termed “luminal” and “basal” with characteristics of stages of urothelial differentiation, and that remarkably reflect the luminal and basal-like molecular subtypes of breast cancer. Patients with basal-like UC have a significantly worse overall survival. Methods: A total of 215 HG muscle-invasive UC tumors from the MDACC (n=75) and TCGA (n=140) were used to make intrinsic subtype calls using gene expression profiling (MDACC: DASL [cDNA-mediated Annealing, Selection, extension, and Ligation] and TCGA: RNA seq). Basal and luminal subtype calls were derived using previously published subtype classifiers (Damrauer et. al. PNAS, 2014 and Choi et. al. Cancer Cell, 2014). Patients were classified into AA and non-AA (white, Hispanic, or Asian) based upon self-reported race. Results: In total there were 16 and 199 tumors from AA and non-AA patients respectively. In non-AA patients, the proportion of tumors that were classified as basal and luminal were approximately equal (93 and 106 respectively), while in AA patients, there was enrichment of basal tumors (12 basal and 4 luminal) (p=0.03735, Fisher’s exact test). Conclusions: AA patients are enriched in the basal molecular subtype of UC. Similar findings have been previously documented in AA women with breast cancer. The enrichment of basal UC in AAs suggests that a biological explanation may in part underlie the poor outcomes seen in AA patients. Future studies will explore the prognostic and predictive implications of basal subtype in AA patients with UC.