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Lung Metastases Versus Second Primary Lung Cancers in Patients with Primary Urothelial Carcinoma of the Bladder: A National Population-Based Assessment

BACKGROUND: The work-up and diagnosis of indeterminate lung nodules at time of bladder cancer diagnosis may delay or change treatment. OBJECTIVE: To quantify the incidence of synchronous and metachronous lung cancers in adults with bladder cancer and compare these rates to the incidence of bladder cancer metastases in the lung. METHODS: We retrospectively analyzed all adults diagnosed with bladder cancer in the Surveillance, Epidemiology and End Results (SEER) registry (2010– 2015) and identified second primary lung cancers defined as being either synchronous (diagnosed within 6 months of bladder cancer diagnosis) or metachronous (more than 6 months following index bladder cancer diagnosis). The risk of second primary lung cancers were reported as a standardized incidence ratio (SIR) reflecting observed and expected case ratios. RESULTS: A total of 88,335 patients diagnosed with bladder cancer were included. Among adults with NMIBC (n = 66,071) and MIBC (n = 18,879), 0.3% and 3.9% had bladder cancer metastatic to the lungs at diagnosis. Synchronous second primary lung cancers were diagnosed in 0.4% and 0.7% of patients with NMIBC and MIBC, respectively. Compared to the general population, the SIR for synchronous lung cancers among adults with NMIBC was 2.5 (95% CI 2.3– 2.9) and was 4.7 (95% CI 4.0– 5.6) for adults with MIBC. CONCLUSIONS: Bladder cancer metastatic to the lung is more common in adults with MIBC compared to NMIBC. There are similar frequencies of synchronous second primary lung cancers regardless of initial bladder cancer stage.