What Is Bladder Cancer?

Bladder cancer starts when cells that make up the urinary bladder start to grow out of control. As more cancer cells develop, they can form a tumor and, with time, spread to other parts of the body.

The bladder is a hollow organ in the lower pelvis. It has flexible, muscular walls that can stretch to hold urine and squeeze to send it out of the body. The bladder’s main job is to store urine. Urine is liquid waste made by the 2 kidneys and then carried to the bladder through 2 tubes called ureters. When you urinate, the muscles in the bladder contract, and urine is forced out of the bladder through a tube called the urethra.

Types of bladder cancer

Urothelial carcinoma (transitional cell carcinoma)

Urothelial carcinoma, also known as transitional cell carcinoma (TCC), is by far the most common type of bladder cancer. In fact, if you have bladder cancer it’s almost certain to be a urothelial carcinoma. These cancers start in the urothelial cells that line the inside of the bladder.

Urothelial cells also line other parts of the urinary tract, such as the part of the kidney that connects to the ureter (called the renal pelvis), the ureters, and the urethra. People with bladder cancer sometimes have tumors in these places, too, so all of the urinary tract needs to be checked for tumors.

Other types of bladder cancer

Other types of cancer can start in the bladder, but these are all much less common than urothelial (transitional cell) cancer.

Squamous cell carcinoma

In the US, only about 1% to 2% of bladder cancers are squamous cell carcinomas. Seen with a microscope, the cells look much like the flat cells that are found on the surface of the skin. Nearly all squamous cell carcinomas of the bladder are invasive.

Adenocarcinoma

Only about 1% of bladder cancers are adenocarcinomas. These cancer cells have a lot in common with gland-forming cells of colon cancers . Nearly all adenocarcinomas of the bladder are invasive.

Small cell carcinoma

Less than 1% of bladder cancers are small-cell carcinomas. They start in nerve-like cells called neuroendocrine cells.

Sarcoma

Sarcomas start in the muscle cells of the bladder, but they are very rare.

These less common types of bladder cancer (other than sarcoma) are treated a lot like TCCs, especially early-stage tumors, but if chemotherapy is needed, different drugs might be used.

Start and spread of bladder cancer

The wall of the bladder has many several layers. Each layer is made up of different kinds of cells

Most bladder cancers start in the innermost lining of the bladder, which is called the urothelium or transitional epithelium. As the cancer grows into or through the other layers in the bladder wall, it has a higher stage, becomes more advanced, and can be harder to treat.

Over time, the cancer might grow outside the bladder and into nearby structures. It might spread to nearby lymph nodes, or to other parts of the body. (When bladder cancer spreads, it tends to go to distant lymph nodes, the bones, the lungs, or the liver.)

Invasive vs. non-invasive bladder cancer

Bladder cancers are often described based on how far they have spread into the wall of the bladder:

• Non-invasive cancers are only in the inner layer of cells (the transitional epithelium). They have not grown into the deeper layers.
• Invasive cancers have grown into deeper layers of the bladder wall. These cancers are more likely to spread and are harder to treat.

A bladder cancer can also be described as superficial or non-muscle invasive. These terms include both non-invasive tumors as well as any invasive tumors that have not grown into the main muscle layer of the bladder.

Papillary vs. flat cancer

Bladder cancers are also divided into 2 subtypes, papillary and flat, based on how they grow (see the image above).

• Papillary carcinomas grow in slender, finger-like projections from the inner surface of the bladder toward the hollow center. Papillary tumors often grow toward the center of the bladder without growing into the deeper bladder layers. These tumors are called non-invasive papillary cancers. Very low-grade (slow growing), non-invasive papillary cancer is sometimes called papillary urothelial neoplasm of low-malignant potential (PUNLMP) and tends to have a very good outcome.
• Flat carcinomas do not grow toward the hollow part of the bladder at all. If a flat tumor is only in the inner layer of bladder cells, it’s known as a non-invasive flat carcinoma or a flat carcinoma in situ (CIS).