Bladder Cancer

Every pathologist has their own way of reporting findings on a bladder biopsy. On some reports you may see sentences such as “invasive into the muscularis propria”, “muscularis propria present”, “muscularis propria not identified”, “invasion of the muscularis propria is indeterminate” etc. In this post I will briefly give an overview of the muscularis propria and its significance in the bladder biopsy.

First, what is the muscularis propria? In order to understand what it is and its significance we first must briefly discuss what is normally seen microscopically in a bladder biopsy. When the pathologist looks under the microscope he/she is looking at the different layers that make up the bladder. The most common type of bladder cancer is urothelial cancer. This type of cancer arises from the urothelial cells that line the bladder. These are the cells that line the inside surface of the bladder and are in contact with the urine (which is why sometimes these cancer cells are present in the urine and can be evaluated by urine cytology). Just beneath the urothelial cell layer is the lamina propria. Beneath the lamina propria is a thick muscle layer called the muscularis propria. Urothelial cancer can be non-invasive (also called in situ) which means that the cancer is confined to the urothelial layer. An invasive cancer breaks through the urothelial layer and extends into the lamina propria and may extend into the muscularis propria (in some cases the invasive cancer may even extend beyond the bladder and into structures such as the prostate or uterus that are next to the bladder). The presence or absence of the muscularis propria becomes important when there is an invasive urothelial cancer. The reason that the muscularis is important is because the presence of tumor in the muscularis propria results in a higher cancer stage. The treatment for urothelial cancer may differ depending on the stage (staging will be discussed in later post). Therefore, in cases where the biopsy has invasive cancer, but the muscularis propria was not present in the biopsy (for example the report may say something like “Invasive high grade urothelial carcinoma. Muscularis propria is not identified” ), it may be necessary for the urologist to get another biopsy that contains muscularis propria to get an accurate cancer stage.

Some pathologists will report the absence of muscularis propria even when the cancer is non-invasive (for example the report may say something like “Non-invasive high grade urothelial carcinoma. Muscularis propria is not identified” or “Flat urothelial carcinoma in situ. Muscularis propria is not identified. ), in these cases since the cancer is non-invasive the absence of muscularis propria in the biopsy is of no concern. In some cases of invasive cancer it is difficult to determine if the invasive cancer involves muscularis propria (for example the report may say something like “Invasive high grade urothelial carcinoma. Invasion of muscularis propria cannot be determined with certainty” ). In such cases, the urologist may decide to obtain a repeat biopsy in order to more adequately determine the tumor stage. In summary, the presence or absence of muscularis propria on a bladder biopsy is only important when the tumor is invasive. Absence of muscularis propria in a biopsy with invasive cancer may necessitate further biopsies to adequately stage the tumor.

Daniel Fajardo MD PhD