Bladder cancer is a malignant tumour that starts in the cells of the bladder. Malignant means that it can spread, or metastasize, to other parts of the body.
The bladder is part of the urinary system. It is a hollow, balloon-shaped organ with a flexible, muscular wall. The bladder stores urine. Urine is made by the kidneys, where it collects in the renal pelvis. It passes to the bladder through 2 tubes called ureters. Urine passes from the bladder and out of the body through a tube called the urethra.
Cells in the bladder sometimes change and no longer grow or behave normally. These changes may lead to non-cancerous, or benign conditions, such as a urinary tract infection. They can also lead to benign tumours, such as papilloma or a fibroma. Benign conditions and tumours are not cancerous. But in some cases, changes to bladder cells can cause bladder cancer.
Most often, bladder cancer starts in cells of the urothelium (also called the transitional epithelium). The urothelium lines the inside of the bladder, ureters, urethra and renal pelvis. It is made up of urothelial cells, or transitional cells. Cancer that starts in urothelial cells is called urothelial carcinoma, or transitional cell carcinoma. Urothelial carcinomas make up more than 90% of all bladder cancers. When the cancer is only in the urothelium, it is called non-invasive bladder cancer. If the cancer spreads into the connective tissue or muscle in the wall of the bladder, it is called invasive bladder cancer.
Rare types of bladder cancer can also develop. These include squamous cell carcinoma and adenocarcinoma. Urothelial carcinoma can also start in the renal pelvis or ureters, but this is less common.
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