Frequency of Low Grade T1 Bladder Cancer Has Decreased But Continues to Vary by Institution
Low grade but invasive urothelial cancers are rare and in 2004, the World Health Organization switched from a three-tier to the current two-tier grading system: high-grade (HG) and low-grade (LG) to reduce tumor heterogeneity. We sought to evaluate the incidence and factors associated with the diagnosis of LG T1 bladder cancer since the adoption of the 2004 grading system.
The Surveillance, Epidemiology, and End Reports (SEER: 2004-2014) and the National Cancer Database (NCDB: 2004-2015) were queried for all patients diagnosed with T1 bladder cancer. The proportion of T1 patients with LG disease was trended over time. Logistic regression was used to determine factors associated with a diagnosis of LG (compared to HG), including year of diagnosis. Overall survival (OS) and cancer-specific (CSS) were compared between the groups.
Within SEER, 34,735 patients were diagnosed with T1 bladder cancer. The percentage of LG cancers decreased from 33.4% in 2004 to 15.6% in 2014 (chi-squared p
Since the adoption of the current bladder cancer grading system, the percentage of T1 diagnoses documented as LG has declined substantially over time but continues to vary widely by institution. This variability raises concerns for grading misclassification within the current system. Given the worse OS and CSS for HG T1, the misclassification of T1 disease as LG could have a negative impact on survival.