Where does bladder cancer start?

Bladder cancer starts in the bladder, a hollow, balloon-shaped organ in the lower part of the abdomen that stores urine. It occurs when cells in the bladder start to grow without control.

Almost all bladder cancers begin in the urothelial cells that line the inside of the bladder. This type is called urothelial carcinoma, also known as transitional cell carcinoma. These cells are also called transitional cells because they can stretch when the bladder is full of urine and shrink when it is empty.

The National Cancer Institute puts urothelial carcinoma at more than 90% of bladder cancers. Squamous cell carcinoma accounts for 2% to 7%, and adenocarcinoma about 2%. Small cell carcinomas and sarcomas of the bladder are rarer still.

How deep it goes matters more than where it sits

The bladder wall is built in layers, like a coat with a lining. Cancer starts at the innermost layer and the whole staging system tracks how far down it has traveled.

• Ta and Tis stay in the lining itself. Ta grows outward into the hollow space as a small frond. Tis, called carcinoma in situ, spreads flat along the surface.
• T1 has broken through into the lamina propria, the thin connective tissue just beneath the lining.
• T2 has reached the muscularis propria, the thick muscle that squeezes the bladder empty.
• T3 has gone past the muscle into the fat around the bladder.
• T4 has reached a nearby organ or the wall of the pelvis or abdomen.

The line between T1 and T2 is the one that changes everything. Ta, Tis, and T1 are grouped as non-muscle-invasive. NCI reports that 70% to 80% of people are in that group at diagnosis. These are usually treated by scraping the tumor out through a scope, sometimes followed by medicine placed directly into the bladder, and the bladder itself is kept.

Once the muscle is involved, treatment gets much more serious, and can involve removing the bladder or combining chemotherapy with radiation.

Why the cancer sometimes shows up somewhere else

Here is the part that surprises people. The same urothelial lining does not stop at the bladder. NCI describes it running from the renal pelvis, where urine collects inside the kidney, down through the ureters and into the upper urethra.

All of that tissue is exposed to the same urine carrying the same chemicals for the same number of years. So the whole tract can be at risk, not just one spot. That is why a new tumor can appear in a different part of the urinary system later, and why follow-up after bladder cancer looks at more than the bladder.

What this means for follow-up

Non-muscle-invasive bladder cancer comes back often, which is why surveillance is built into care. That usually means cystoscopy, a look inside the bladder through a thin scope, repeated on a schedule for years.

Two things are worth doing. Keep the surveillance appointments even when you feel completely well, since recurrences are usually silent. And report any blood in the urine between visits rather than waiting for the next one.

Your healthcare team can explain more about the type of bladder cancer in your situation.