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The Normal Bladder
Your bladder is a hollow pelvic organ with flexible, muscular walls that stores
urine. The average adult bladder holds about 2 cups of urine. Urine is made by
the 2 kidneys and carried to the bladder by 2 tubes called ureters. The bladder
empties the urine through another tube called the urethra. In women, the urethra
is a very short tube that ends just in front of the vagina. In men, the urethra is
longer. It passes through the prostate gland and the penis, and ends at the tip
of the penis.
The wall of the bladder has several layers. A layer of urothelial cells
(also called transitional
cells) lines the inside of the kidney, ureter, bladder,
and urethra. This layer is called the urothelium or transitional epithelium.
Beneath the urothelium, there is a thin zone of connective tissue
called the lamina propria.
The next deeper layer is a wider zone of muscle tissue called the muscularis propria.
Beyond this muscle, another zone of fatty connective tissue separates
the bladder from other nearby organs. These layers are very important
in understanding bladder cancer. As the cancer penetrates through these
layers into the wall of the bladder, it becomes harder to treat.
Types of Bladder Cancer
Bladder tumors are grouped into several types by the way they appear
under a microscope. The 4 main types of cancers that affect the bladder
are:
- urothelial carcinoma or transitional cell carcinoma
- squamous cell carcinoma
- adenocarcinoma
- small cell
These same types of cancer can also grow in the lining of the kidney
(called the renal pelvis),
the ureters, and the urethra. In fact, patients with bladder cancer
sometimes have a similar type of cancer in the lining of the kidneys,
ureters, or urethra. Therefore, a complete evaluation of the urinary
system is recommended for patients diagnosed with a cancer of the
kidney, bladder, ureter, or urethra.
Urothelial cells line the bladder. Urothelial
(transitional cell) carcinoma is the most common form of
bladder cancer. It accounts for more than 90% of these cancers.
Only about 4% of bladder cancers are squamous cell carcinomas.
Under a microscope, the cells look much like cells from skin cancers.
Nearly all squamous cell carcinomas are invasive.
Only about 1% to 2% of bladder cancers are adenocarcinomas. The
cells have a lot in common with gland-forming cells of intestinal
cancers. Nearly all adenocarcinomas of the bladder are invasive.
About 1% of bladder cancers are small
cell.
Urothelial carcinomas, squamous cell carcinomas, small cell cancers,
and adenocarcinomas may respond differently to radiation and
chemotherapy. Treatment recommendations for some patients may be
influenced by the type of cancer.
Rhabdomyosarcoma
is a very rare cancer that can start in the bladder but more often
affects other tissues and organs.. It usually affects infants and is
seldom found in adults. It is not discussed further in this document
but is described in a separate American Cancer Society document,
"Rhabdomyosarcoma."
Subtypes of Urothelial Tumors
Not all urothelial tumors are the same. They are divided into several
subtypes according to whether they are noninvasive or invasive and whether
their shape is papillary
or flat.
Noninvasive urothelial
tumors: The cancer is only in the innermost layer of the
bladder, the urothelium. It has not spread to deeper layers of the
bladder.
Invasive urothelial
tumors: The cancer has spread from the urothelium to the
deeper layers of the bladder wall. In the past, some doctors used this
term only when cancer had spread to the thickest and deepest muscle
layer of the bladder (called the muscularis propria).
Currently, any bladder cancer not limited to the urothelium is
classified as invasive. But it is very important to determine exactly
how far into the bladder wall the cancer has invaded. Invasion of the
thick, deep muscle layer of the bladder is much more serious than
invasion that is limited to the superficial connective tissue layer
(lamina propria) or the superficial, thin, muscle layer (muscularis
mucosa).
Superficial urothelial
tumors: This category includes bladder cancers that are
noninvasive as well as some invasive cancers that have not spread
deeply into the bladder wall. The cancer may only be in the layers of
urothelial cells closest to the inside of the bladder, or it may have
also spread to the thin layer of connective tissue (called the lamina
propria) just beneath the urothelial cells. Once a cancer has invaded
the bladder's main muscle layer, it is not considered superficial.
Papillary urothelial
tumors: Papillary tumors have slender finger-like
projections that grow into the hollow center of the bladder. They are
sometimes said to resemble a branching type of cactus plant. Some
papillary urothelial tumors grow only toward the center of the bladder.
These are called noninvasive
papillary urothelial tumors.
- Papillomas
are a benign type of papillary urothelial tumor. Since they are not
cancerous, these tumors never spread to other parts of the body. They
are successfully removed by surgery and rarely grow back. Patients with
papillomas very rarely develop another papillary tumor elsewhere in
their urinary system.
- Papillary
urothelial neoplasms of low malignant potential are cancers.
These are usually successfully treated by surgical removal. But it is
not unusual for patients with these tumors to develop one or more
papillary tumors later on in other areas of their urinary system. Most
of these other tumors resemble the original tumor, but occasionally the
new tumor may be cancerous or even invasive.
- Papillary
urothelial carcinoma is a papillary tumor showing variable
degrees of abnormality of the shape, size, and arrangement of cells.
Those with relatively slight abnormality are called low grade. Although
they rarely invade into the bladder wall, they often return after
surgery. Carcinomas with greater abnormalities, called high-grade
carcinomas, are more likely to invade into the bladder wall or even
spread to other parts of the body.
Some papillary carcinomas grow inward toward the center and also grow
outward into the bladder wall. These are called invasive papillary urothelial
carcinomas.
Flat urothelial tumors:
Flat urothelial carcinomas do not grow toward the hollow part of the
bladder at all. Some of these only involve the layer of cells closest
to the inside or the hollow part of the bladder. These are called noninvasive flat
urothelial carcinomas. Another name for noninvasive flat urothelial
carcinomas is flat
carcinoma in situ (CIS). Some flat urothelial carcinomas
invade the deeper layers (away from the hollow part), particularly the
muscle layer. These are called flat
invasive urothelial carcinomas.
Revised: 08/08/2006
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