The bladder is a muscular balloon-shaped organ that can expand and contract (get smaller) depending on how much urine is in the bladder. ^{1 ,2}

The bladder is made up of four layers of tissue:¹

• Urothelium– this layer consists of cells that keep the urine in the bladder and prevent it being absorbed into the body. It is the first layer inside of the bladder.
• Lamina propria– is next to the urothelium layer and consists of blood vessels.
• Muscularis propria– this is the thickest of all layers, and it is responsible for contracting the bladder to empty urine.
• Perivesical tissue– surrounds all the other layers of the bladder and consists mainly of fatty tissue to help protect the bladder.

Cancer of the bladder occurs when cells in the bladder grow and divide in an abnormal way.¹

The most common type of bladder cancer is urothelial carcinoma, which accounts for approximately 85% of all bladder cancers.³

Other types of bladder cancer include squamous cell carcinoma and adenocarcinoma. These types of cancer only account for a small percentage of bladder cancers (1-2%), however they tend to be aggressive (grow quickly).³

Bladder cancer can be either:

• Non-muscular-invasive bladder cancer– where cancer cells are only found in either of the first two layers of the bladder; the urothelium cells (the innermost cells of the bladder) or the next layer of tissue called the lamina propria.^1,3
• Muscular-invasive bladder cancer– where cancer cells have spread beyond the first two layers of the bladder into the muscle layer and in some cases, into nearby tissue.^1,3

It is not common for bladder cancer to be passed down from generation to generation, although people can inherit genetic mutations from their parents which increase the risk of bladder cancer. ¹⁵

Additionally, people can inherit impairments in removing waste products (such as toxins) from the body, making them more exposed to environmental cancer-causing toxins such as tobacco and industrial chemicals, increasing their cancer risk. ¹⁵

The most common system used to stage bladder cancer is called the TNM system, which stands for: ⁵

• Tumour (T) – which describes how big the tumour is and how much of the bladder and surrounding tissue has been affected.
• Nodes (N)– describes how many lymph nodes have been affected by the cancer.
• Metastasis (M)– describes if the cancer has spread to other parts of the body.

A biopsy of the tumour will also provide information and a ‘grade’ of the cancer such as how quickly it will grow and the chance of it coming back.⁵

• Low grade– most tumours in the bladder are considered low grade, which means the cancer cells are slow growing and tend not to spread and look like bladder cells.⁵
• High grade– cancer cells look very different to bladder cells and tend to grow quickly and spread to other tissues in the body.⁵