What causes bladder cancer is not always clear, but the risk of developing bladder cancer can be increased by smoking, getting older, long term bladder problems and unsafe exposure to aniline dyes which are used in some industries.

Bladder tumours usually form in cells lining the bladder. Once a tumour begins to enlarge, it may stay in the lining or grow into the wall of the bladder. If untreated, the tumour may then grow into other structures such as lymph nodes.
If the cancer enters the bloodstream it may spread to other areas of the body (metastasis). 

Often the first symptom noticed is blood in the urine, other symptoms such as needing to pass urine more often or feeling as if you need to go but can’t affect about 1/3 of people with early bladder cancer.  As the tumour grows these symptoms affect more people.

The first test to diagnose bladder cancer is usually a urine sample. 
If cancer is suspected, the next step is usually a cytoscopy (a tube is inserted into the urethra to allow the doctor to look inside the bladder). If there is to be a tumour the doctor can take a small sample (biopsy) for testing.
CT or MRI scans are also used to scan the body to see if the cancer has spread to other areas.

Treatment depends on the size of the tumour and how much it has grown into the bladder wall.