This article will help you read and understand your pathology report for urothelial carcinoma.
by Jason Wasserman, MD FRCPC, reviewed July 30, 2020
The bladder is a hollow organ located in the pelvis. The purpose of the bladder is to store urine and then to release it out of the body through a tube called the urethra. Urine is made in the kidneys and travels to the bladder by two long tubes called ureters. Urine travels from the bladder to the outside of the body through the urethra.
The inside of the bladder is lined by specialized cells called urothelial cells. These cells form a barrier on the inner surface of the bladder called an epithelium. The tissue directly below the epithelium is called the lamina propria. The inside of the ureters and urethra are also lined by urothelial cells.
The diagnosis of urothelial carcinoma is usually made after a pathologist looks at a urine sample or biopsy taken from the bladder through a microscope. The entire tumour is then removed in a procedure called a resection.
When the tumour cells are only seen in the epithelium, the disease is called urothelial carcinoma in situ. When the tumour cells spread beyond the epithelium and into the lamina propria, the diagnosis changes to urothelial carcinoma. The movement of tumour cells from the epithelium into the lamina propria is called invasion.
Pathologists use the word grade to describe how different the tumour cells look compared to the normal, healthy urothelial cells. The size, shape, and colour of the tumour cells is used to determine the grade.
Based on the way the tumour cells look when examined under the microscope, urothelial carcinoma is divided into two grades:
Most urothelial carcinomas are high grade.
There are different kinds of urothelial carcinoma and each is called a histologic type. Your pathologist will determine the type by examining the tissue under the microscope and looking at the size and shape of the tumour cells and the way they stick together as they grow.
The most common type is called conventional. Because it is so common, most reports will leave out the word conventional and simply say “invasive urothelial carcinoma”. However tumours that are made up of a less common variant are given a special name. If your pathologist sees one of these less common types in your tissue sample, it will be described in your pathology report.
Less common histologic types of urothelial carcinoma include:
The nested, microcystic, sarcomatoid, micropapillary, and poorly differentiated types are more likely to spread deeper into the bladder wall and to other parts of the body such as lymph nodes. The spread of tumour cells to another part of the body is called a metastasis.
This is the size of the tumour measured in centimetres (cm). The tumour is usually measured in three dimensions but only the largest dimension is described in your report. For example, if the tumour measures 4.0 cm by 2.0 cm by 1.5 cm, your report will describe the tumour as being 4.0 cm.
There is a thick bundle of muscle in the wall of the bladder called the muscularis propria. When the bladder is full of urine, the muscularis propria squeezes which forces all of the urine out of the bladder and into the urethra.
The muscularis propria is found in the middle of the wall of the bladder below the lamina propria. Tumour cells that spread beyond the lamina propria enter the muscularis propria. The movement of tumour cells into the muscularis propria is called invasion.
When examining a tissue sample from your bladder under the microscope, your pathologist will look for muscularis propria. If there is no muscularis propria in the tissue sample, your pathologist will not be able to say if there is invasion of the muscularis propria.
Invasion of the muscularis propria by tumour cells increases the tumour stage (see Pathologic stage below) and is associated with worse prognosis.
All urothelial carcinomas start in the epithelium on the inner surface of the bladder, ureter, or urethra. Tumour extension describes how far the tumour cells have spread from the epithelium into the deeper layers of tissue under the epithelium. The movement of tumour cells from the epithelium into the tissue below is called invasion.
The extent of invasion will be described in your report as follows:
The extent of invasion plays a very important role in the staging of urothelial carcinoma (see Pathologic stage below) and is the most important feature when determining the type of treatment that will be offered.
Blood moves around the body through long thin tubes called blood vessels. Another type of fluid called lymph which contains waste and immune cells moves around the body through lymphatic channels.
Tumour cells can use blood vessels and lymphatics to travel away from the tumour to other parts of the body. The movement of tumour cells from the tumour to another part of the body is called metastasis.
Before tumour cells can metastasize, they need to enter a blood vessel or lymphatic. This is called lymphovascular invasion.
Lymphovascular invasion increases the risk that tumour cells will be found in a lymph node or a distant part of the body such as the lungs.
Lymph nodes are small immune organs located throughout the body. Tumour cells can travel from the tumour to a lymph node through lymphatic channels located in and around the tumour (see Lymphovascular invasion above). The movement of tumour cells from the tumour to a lymph node is called a metastasis.
Your pathologist will carefully examine all lymph nodes for tumour cells. Lymph nodes that contain tumour cells are often called positive while those that do not contain any tumour cells are called negative. Most reports include the total number of lymph nodes examined and the number, if any, that contain tumour cells.
Finding tumour cells in a lymph node is important because it is associated with a higher risk that the tumour cells will be found in other lymph nodes or in a distant organ such as the lungs.
A margin is any tissue that has to be cut by the surgeon in order to remove the tumour from your body. In urothelial carcinoma, a margin is considered positive when there is no distance between the tumour and the cut edge of the tissue. A negative margins means that no tumour cells were seen at the cut edge of the tissue.
A positive margin is associated with a higher risk that the tumour will grow back (recur) in the same location after treatment.
The pathologic stage for urothelial carcinoma is based on the TNM staging system, an internationally recognized system originally created by the American Joint Committee on Cancer.
This system uses information about the primary tumour (T), lymph nodes (N), and distant metastatic disease (M) to determine the complete pathologic stage (pTNM). Your pathologist will examine the tissue submitted and give each part a number. In general, a higher number means more advanced disease and worse prognosis.
Urothelial carcinoma is given a tumour stage from 1 to 4 based on the amount of tumour extension (see Tumour extension above).
Urothelial carcinoma is given a nodal stage between 0 and 3 based on the number of lymph nodes that contain cancer cells and the location of those lymph nodes.
Urothelial carcinoma is given a metastatic stage of 0 or 1 based on the presence of tumour cells at a distant site in the body (for example the lungs). The metastatic stage can only be assigned if tissue from a distant site is submitted for pathological examination. Because this tissue is rarely present, the metastatic stage cannot be determined and is listed as pMX.