[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Lower urinary tract and male genital system](https://durgical.com/en/general-pathology/areas/urinary-male/) › Urothelial carcinoma: pathogenesis

# Urothelial carcinoma: pathogenesis

- Mechanism

Chemicals in urine bathe the whole urothelium, so bladder cancer recurs and can appear anywhere from the renal pelvis to the urethra.

Updated Nov 12, 2026

## Key points

- Smoking is the most important risk factor; aromatic amines (2-naphthylamine, benzidine) are occupational.
- Other carcinogens: cyclophosphamide, arsenic, aristolochic acid, pelvic radiation, chronic schistosomiasis (squamous carcinoma).
- Papillary pathway: FGFR3 activation, often 9p/9q loss (CDKN2A); many recurrences, few invasions.
- Flat pathway: TP53 and RB loss, carcinoma in situ, then invasion.
- Field effect: tumours are multifocal and recur in other sites of the urinary tract.

## What it is

Urothelial (transitional cell) carcinoma is the commonest bladder cancer and also arises in the renal pelvis, ureter and urethra. Carcinogens are excreted in urine and act on all of the urothelium: tobacco smoke, aromatic amines (aniline dyes, rubber), cyclophosphamide, arsenic and aristolochic acid. Two main pathways lead to cancer: low-grade papillary tumours with FGFR3 and HRAS mutations that recur but seldom invade, and flat carcinoma in situ with TP53 and RB pathway loss that leads to invasive cancer. Lynch syndrome raises the risk of upper-tract tumours.

## Step by step

- Carcinogens are absorbed, activated in the liver and excreted into urine.
- Stored urine keeps them in contact with the urothelium, mostly the bladder.
- Loss of chromosome 9 genes (such as CDKN2A) is an early common step.
- FGFR3 or HRAS mutations drive low-grade papillary growth.
- TP53 and RB pathway loss drive flat, high-grade carcinoma in situ.
- High-grade lesions invade the lamina propria and muscularis propria and metastasize.

## Two pathways of urothelial carcinogenesis

| Pathway | Precursor | Typical mutations | Behaviour |
| --- | --- | --- | --- |
| [Low-grade papillary pathway](https://durgical.com/en/conditions/bladder-cancer/) | Noninvasive papillary tumour | FGFR3, HRAS, chromosome 9 loss | Frequent recurrence, rarely invades |
| Flat high-grade pathway | Carcinoma in situ | TP53, RB1, CDKN2A | Invasive, metastatic disease |

## Clinical notes

- Painless hematuria in an older smoker is bladder cancer until proven otherwise.
- Aristolochic acid in some herbal remedies causes both interstitial nephritis and upper-tract urothelial carcinoma.

## Memory aid

What the body throws into urine, the bladder must hold: smoke, dyes and drugs.

## Test yourself

Think of the answer, then tap the question to see it.

## What is the most important risk factor for urothelial carcinoma?

Cigarette smoking.

## Which gene is typically mutated in low-grade papillary urothelial tumours?

FGFR3.

## Why are urothelial tumours often multifocal?

Carcinogens in urine act on the whole urothelial field, from the renal pelvis to the urethra.

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## Elsewhere in DurgiPedia

- [Chemical carcinogens: initiation, promotion and the table to know](https://durgical.com/en/general-pathology/chemical-carcinogens-initiation-promotion-and-the-table-to-know/)
- [Tobacco: how smoking injures tissue](https://durgical.com/en/general-pathology/tobacco-how-smoking-injures-tissue/)
- [Multistep carcinogenesis: the adenoma–carcinoma sequence](https://durgical.com/en/general-pathology/multistep-carcinogenesis-the-adenoma-carcinoma-sequence/)

## Connections

## Related 5

- [Urothelial tumours: morphology, grade and stage](https://durgical.com/en/general-pathology/urothelial-tumours-morphology-grade-and-stage/)
- [Other bladder tumours](https://durgical.com/en/general-pathology/other-bladder-tumours/)
- [Chemical carcinogens: initiation, promotion and the table to know](https://durgical.com/en/general-pathology/chemical-carcinogens-initiation-promotion-and-the-table-to-know/)
- [Tobacco: how smoking injures tissue](https://durgical.com/en/general-pathology/tobacco-how-smoking-injures-tissue/)
- [Multistep carcinogenesis: the adenoma–carcinoma sequence](https://durgical.com/en/general-pathology/multistep-carcinogenesis-the-adenoma-carcinoma-sequence/)

## Related conditions 4

- [Bladder cancer](https://durgical.com/en/conditions/bladder-cancer/)
- [Lynch syndrome (hereditary non-polyposis colorectal cancer)](https://durgical.com/en/conditions/lynch-syndrome/)
- [Schistosomiasis](https://durgical.com/en/conditions/schistosomiasis/)
- [Tobacco use disorder](https://durgical.com/en/conditions/tobacco-use-disorder/)

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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Bladder Cancer](https://www.ncbi.nlm.nih.gov/books/NBK536923/) (StatPearls (NCBI Bookshelf), 2024); [Bladder Cancer Treatment](https://www.cancer.gov/types/bladder/patient/bladder-treatment-pdq) (National Cancer Institute, 2025).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

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Source: https://durgical.com/en/general-pathology/urothelial-carcinoma-pathogenesis/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/urothelial-carcinoma-pathogenesis/