Bladder cancer

The bladder is a muscular sac that stores urine. It is located in the pelvis and is part of the urinary system.

As well as the bladder, the urinary system includes two kidneys, two tubes called ureters leading into the bladder, and another tube called the urethra leading out of the bladder.

In women, the urethra is a short tube that opens in front of the birth canal (vagina). In men, the tube is longer and passes through the prostate and down the penis.

The kidneys produce urine, which travels to the bladder through the ureters. The bladder is like a balloon and inflates as it fills. When it is time to go to the toilet, the bladder muscle contracts and urine is passed through the urethra and out of the body.

There are four main layers of tissue in the bladder:

• urothelium – the innermost layer. It is lined with cells that stop urine being absorbed into the body. These cells are called urothelial cells
• lamina propria – a layer of tissue and blood vessels surrounding the urothelium
• muscularis propria – the thickest layer. It consists of muscle that contracts to empty the bladder
• perivesical tissue – the outermost layer. It is made up mostly of fatty tissue that separates the bladder from nearby organs.

There are three main types of bladder cancer. They are named after the cell type in which the cancer first develops.

Urothelial carcinoma

About 80–90% of all bladder cancers start from the urothelial cells that line the bladder wall. This is sometimes called transitional cell carcinoma.

Urothelial carcinoma can be papillary or flat:

• Papillary urothelial carcinoma – has slender, finger-like projections and grows towards the hollow centre of the bladder. Most urothelial carcinomas are papillary.

• Flat urothelial carcinoma – grows flat on the bladder wall without developing any finger-like projections. Carcinoma in situ is a type of flat urothelial carcinoma.

Urothelial carcinoma can also occur in the ureters and kidneys (see next section).

Squamous cell carcinoma

This type of cancer starts in the thin, flat cells in the lining of the bladder. It accounts for 1–2% of all bladder cancers and is more likely to be invasive.

Adenocarcinoma

This cancer develops from the mucus-producing cells of the bladder. It makes up about 1% of all cases and is likely to be invasive.

Other types of bladder cancer

Rarer types of bladder cancer include sarcomas (starting in the muscle) and aggressive forms called small cell carcinoma, plasmacytoid carcinoma and micropapillary carcinoma.

Research shows that people with certain risk factors are more likely to develop bladder cancer. These include:

• smoking – cigarette smokers are up to six times more likely than nonsmokers to develop bladder cancer
• older age – most people with bladder cancer are over 60, and the risk increases with age
• being male – men are three times more likely than women to develop bladder cancer
• chemical exposure at work – chemicals called aromatic amines, benzene products and aniline dyes have been linked to bladder cancer; these chemicals are used in rubber and plastics manufacturing and in the dye industry and sometimes in the work of painters, machinists, printers, hairdressers and truck drivers
• chronic infections – squamous cell carcinoma has been associated with urinary tract infections (including parasite infections, although these are very rare in Australia) and untreated bladder stones
• long-term catheter use – long-term urinary catheter use may be linked with squamous cell carcinoma
• previous cancer treatments – treatments that have been linked to bladder cancer include the chemotherapy drug cyclophosphamide and radiotherapy to the pelvic area (sometimes given for prostate cancer and gynaecological cancers)
• diabetes treatment – diabetes medicines containing pioglitazone can increase the risk of bladder cancer
• personal or family history – a small number of bladder cancers are associated with an inherited gene.