Over the 21-year period, there was a decline in the diagnosis of squamous cell carcinoma (SCC) by over 2% and a marked increase in subtype histologies (micropapillary, sarcomatoid, plasmacytoid, neuroendocrine). After adjusting for clinical variables (sex, race, age at cystectomy, TNM staging), later year of diagnosis remained independently associated with increased odds of identifying neuroendocrine carcinoma (OR 1.07) and other subtype histologies (OR 1.16).
These findings carry significant clinical implications. Subtype histologies are frequently associated with aggressive tumor biology, including advanced stage at presentation and unpredictable sensitivity to chemotherapy or immunotherapy. Consistent with this, our study found that variant subtypes were more likely to present with ≥T3 disease, nodal involvement, and metastases at diagnosis. Importantly, MIBC often exhibits histologic heterogeneity: many tumors harbor both urothelial carcinoma and variant components. Recognition of even focal variant differentiation can substantially influence treatment decisions.
During our study period, successive editions of the WHO pathology classification guidelines for bladder tumors described improved diagnostic methodologies for the detection of subtype histologies, including immunohistochemical techniques and identification of molecular and genetic alterations in tumors. Our finding of increased subtype histology diagnoses over time may reflect a national diffusion of these improved methodologies from specialized cancer centers into the community, as well as an overall increased number of genitourinary pathology specialists in the country.
For the practicing urologist, these findings impact care across the entire disease trajectory. Earlier and more accurate identification of subtype histologies facilitates the timely initiation of appropriate therapies. As artificial intelligence and machine learning are integrated into histopathologic workflows, we may soon see histology-driven algorithms that refine prognosis, correlate with molecular profiles, and identify novel response phenotypes to optimize oncologic outcomes.
In summary, this study highlights a positive, national shift toward greater recognition of histologic heterogeneity in MIBC. As our understanding of histological subtypes and divergent differentiation expands, integrating detailed histologic assessment into routine workflows will be essential to advance precision medicine and improve outcomes.
KEY TAKEAWAYS:
- Squamous cell carcinoma (SCC) diagnoses are declining, while other subtypes are on the rise.
- From 2000 to 2020, the proportion of SCC diagnosis decreased from 5.8% to 3.7%, while other subtype histologies (micropapillary, sarcomatoid, plasmacytoid) more than doubled from 2.0% to 5.2%.
- After controlling for sex, race, age, and TNM stage, each 3-year interval was associated with a 7% increase in neuroendocrine carcinoma and 16% increase in other subtype histologies.
- Diagnostic guidelines and pathologist expertise are likely drivers.
- The study period coincided with three editions of WHO classification of bladder tumors.
- There is growing access to immunohistochemistry and widespread genitourinary pathology specialization.
- Trends in bladder cancer histopathology have broad implications for clinical practice and future research
- SEER is a large, nationally representative dataset that offers insight into real-world diagnostic patterns.
- Further research should focus on granular data demonstrating whether trends in histology diagnosis correlate with changes in risk stratification, treatment patterns, and outcomes.
Written by: Aidan Weitzner, BS, and Brendan K. Wallace, MD,
Brady Urological Institute, Johns Hopkins Hospital, Baltimore, MD
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