Racial differences in the distribution of bladder cancer metastases: a population-based analysis

Introduction: Bladder cancer is the second most common genitourinary malignancy in the United States. The incidence of bladder cancer rises with age, and it is two times more common in Caucasians than in African-Americans (23.1 vs. 12.6 cases/100,000 persons). We aimed to investigate the racial and age-related differences in the distribution of metastasis in a large, contemporary cohort of metastatic bladder cancer patients.

Material and methods: Within the National Inpatient Sample database (2008-2015) we identified 5,767 patients with metastatic bladder cancer. Trend test, Chi-square test and multivariable logistic regression models were used to evaluate the relationship between ethnicity, age, and site of metastasis.

Results: Of 5,767 patients with metastatic bladder cancer, 598 (10.4%) were African-American. Lung was the most common metastatic site in African-Americans (28.6%) vs. bone in Caucasians (21.7%). Overall, African-Americans showed higher rates of lung (+10.2%), liver (+7.5%) and bone (+5.2%) metastases, compared to Caucasians (all p <0.01). Brain metastases were rare in both ethnicities (3.3 vs. 2.4%; p = 0.2). Rates of exclusive bone, lung or liver metastases increased with age, but were higher in African-Americans, regardless of age strata. In the multivariable logistic regression models, African-American ethnicity independently predicted higher risk of lung (Odds ratio: 1.69), liver (odds ratio: 1.50) and bone (odds ratio: 1.27) metastases, relative to Caucasians. Moreover, a dose-response effect was found after combining the three main risk factors for developing bone metastases, namely African-American ethnicity, younger age and male gender.

Conclusions: Racial differences exist in the distribution of metastatic bladder cancer metastasis. Moreover, based on higher risk of bone metastases in African-American patients, bone imaging may be warranted in this patient population, especially in the presence of other risk factors for bone metastases, namely male gender or younger age.