Bladder Cancer is the 10th most common cancer in the world, with over 500 000 people diagnosed worldwide every year (1). It occurs when cells in the bladder begin to mutate and multiply in an uncontrolled manner. However, this multiplication and abnormal behaviour can also lead to benign tumours or even urinary tract infections (UTIs). In cases of bladder cancer, it will often originate in the cells that make up the lining of the bladder, referred to as urothelial cells, and thus this bladder cancer is called urothelial carcinoma (2).
Urothelial carcinomas make up more than 90% of all bladder cancers. They are often diagnosed at an early stage when they have not grown into the deeper muscle layer of the bladder wall.
Bladder cancer is often divided into 3 groups based on how much it has grown into the bladder wall:
- Non-invasive bladder cancer is only in the inner lining of the bladder (urothelium).
- Non-muscle-invasive bladder cancer has only grown into the connective tissue layer (lamina propria).
- Muscle-invasive bladder cancer has grown into the muscles deep within the bladder wall (muscularis propria) and sometimes into the fat that surrounds the bladder.
There are many types of bladder cancer. The most common include:
- Urothelial carcinoma
- Also referred to as transitional cell carcinoma, this is the most common type of bladder cancers. It starts in the urothelial cells which line the inner bladder. This cancer can be found in more than one place in the urinary tract, including the ureter and urethra.
- Non-invasive urothelial carcinoma
- These carcinomas are classified as papillary or flat, depending on how they grow.
- Papillary: appear like small fingers growing towards the centre of the bladder, can be low or high grade.
- Flat: found on the bladder lining, high grade (more likely to grow into deeper layers of the bladder wall).
- Often referred to as carcinoma in situ (CIS).
- These carcinomas are classified as papillary or flat, depending on how they grow.
- Invasive urothelial carcinoma
- These carcinomas have grown beyond the inner lining, into the deeper layers of the bladder wall. Sometimes, these cancers will have other types of cells mixed in with the urothelial cells (divergent differentiation), which makes the cancer more aggressive and more likely to be diagnosed at an advanced stage.
Rarer types of bladder cancer, making up less than 10% of cases, include:
- Squamous cell carcinoma
- Often associated with chronic bladder irritation or inflammation, which can be caused by catheters, urinary stones, or chronic UTIs. This cancer is usually invasive, and diagnosed at a later stage.
- Adenocarcinoma
- This makes up less than 2% of bladder cancers, and starts in the gland cells of the bladder. It can spread to another site, so it is vital for doctors to know where it started in order to make a proper diagnosis. This cancer also has a high recurrence rate.
- Urachal cancer
- The urachus is a ligament connecting the navel and bladder, typically formed during fetal development. This ligament has no function in adults, but remains present. Cancerous tumours can develop along the urachus, typically where it joins the top of the bladder.
- Small cell carcinoma
- This is a type of neuroendocrine tumour (NET) that starts in the cells of the neuroendocrine system, which are found in nearly every organ in the body. This cancer is typically high grade, growing and spreading quickly.
- Soft tissue sarcoma
- This cancer starts in the soft tissues of the bladder, such as the muscles, blood vessels, or fat. The main cause for it is having had radiation therapy for another cancer 20 to 30 years prior.
Some benign conditions may also affect the bladder and cause symptoms similar to cancer, such as UTIs, benign papillomas, and urinary tract stones.
Information taken from Canadian Cancer Society unless otherwise indicated.
(1) “Bladder cancer statistics”, World Cancer Research Fund, 2018. https://www.wcrf.org/dietandcancer/cancer-trends/bladder-cancer-statistics
(2) “What is bladder cancer”, Canadian Cancer Society, n.d. http://www.cancer.ca/en/cancer-information/cancer-type/bladder/bladder-cancer/