by Jason Wasserman MD PhD FRCPC
March 3, 2022
Urothelial carcinoma in situ (CIS) is a type of non-invasive cancer that starts in a part of the body called the urinary tract. The urinary tract includes the bladder, ureters, urethra, and kidneys. Urothelial carcinoma in situ arises from specialized urothelial cells that cover the inside surface of these organs and create a barrier called the urothelium. If left untreated, urothelial carcinoma in situ can progress over time into a type of invasive cancer called urothelial carcinoma.
The diagnosis of urothelial CIS is usually made after tissue is removed from a part of the urinary tract such as the bladder in a procedure called a biopsy or transurethral resection (TURBT). The tissue is then sent to a pathologist for examination under a microscope.
When examined under the microscope, the tumour cells in urothelial CIS look very abnormal compared to healthy urothelial cells. For example, the tumour cells are usually larger than normal urothelial cells and the nuclei are hyperchromatic (darker). Pathologists often use the terms atypia or atypical to describe these abnormal tumour cells. Mitotic figures (tumour cells dividing to create new tumour cells) are also usually seen and some may be described as atypical mitotic figures because they are dividing abnormally.
Urothelial CIS is a non-invasive tumour which means that the cells are only seen in the urothelium on the surface of the tissue. Invasion is a word that pathologists use to describe the movement of tumour cells into surrounding tissue. Because pathologists always look for invasion before making the diagnosis of urothelial CIS, your pathology report may say that no invasion was seen or that the tissue was negative for invasion.
A margin is the normal tissue that surrounds a tumour and is removed with the tumour at the time of surgery. A negative margin means that no tumour cells were seen at the cut edge of the tissue. A margin is called positive when there is no distance between the tumour and 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. Most pathology reports for urothelial carcinoma in situ do not include information about margins.