When it comes to bladder cancer, it’s important to note the differences between muscle-invasive and non-muscle-invasive bladder cancer, as it can affect the staging of the cancer.
The “stage” (spread) of bladder cancer may vary from patient to patient, so it’s important to understand the difference between muscle-invasive and non-muscle-invasive bladder cancer.
Between muscle-invasive and non-muscle-invasive bladder cancer, “the main difference has to do with the depth of the cancer invasion within the bladder wall,” Dr. Petros Grivas, a medical oncologist, professor and clinical director of genitourinary cancers program at Fred Hutchinson Cancer Center and the University of Washington, explained during an interview with CURE®.
He noted that once tumor cells have entered the main muscle layer of the bladder wall, it becomes muscle-invasive bladder cancer.
However, non-muscle invasive bladder cancer is when the tumor has not yet entered the main muscle layer of the bladder wall, Grivas said, which he described as “more superficial,” meaning the tumor is at a surface layer near the lumen of the bladder.
A way to determine whether a patient has muscle-invasive or non-muscle-invasive bladder cancer includes a cystoscopy, known as a procedure that looks inside the bladder via a thin tube with a small video camera attached to the end, as the American Cancer Society defines.
The cystoscopy is combined with the surgical removal of the tumor by the urologist with a very careful assessment of the tumor specimen by a pathologist. The procedure, called “TURBT,” may need to be repeated in certain cases aiming for accurate “staging.”
The results from a tumor removal are discussed between a pathologist (scientist studying diseases often using a microscope) and a urologist (doctor specializing in urinary tract conditions) to “help us in that staging, meaning how extensive the cancer is, while examining the patient and also looking at the scans (imaging) is also critical for that assessment,” Grivas explained.
The main difference has to do with the depth of the cancer invasion within the bladder wall. If we think about the bladder cancer arising in the internal part of the bladder — what we call the lumen — where the urine is being collected, this tumor usually can make its way towards the external part of the bladder. So, it starts invading the different layers of the bladder wall and one of those main middle layers in the middle of the way is called muscle or muscularis, (“propria”) term, but let's think about it as the muscle that makes the bladder contract and to send the urine out for urination. So that muscle layer, if it's invaded by the tumor cells, that makes it muscle invasive.
And that's relevant for therapy implications. Because of that particular muscle layer has also little blood vessels and little (“lymphatic”) spaces that may actually generate a risk of cancer cells leaving the bladder and finding an avenue to escape and cause what we call metastasis. So, because of that, we have to think about not only what we see in the CT scan, for example, but also any potential microscopic cells that may or may not be present (elsewhere) in the body.
That's why the muscle layer invasion is important. And we may have a medical oncologist like myself be involved in the (evaluation and possible) treatment of the patient (in addition to urologist, radiation oncologist, etc.) On the contrary, non-muscle-invasive is pretty much when the bladder cancer is more “superficial,” so it has not yet invaded the muscle layer (and remains in) the more “superficial” layers of the bladder.
There are three different types of non-muscle invasive bladder cancer (‘Ta, T1, CIS’) and the urologist who does the exam, cystoscopy and tumor removal looks inside the bladder and takes the cancer out. This goes to pathology and the pathologist along with a urologist can help us in that staging, meaning how extensive the cancer is.
And the T stage — T for tumor — can help us understand if it's muscle-invasive or not, depending on the depth of invasion, we also take into account the CT scan (imaging studies) that we do and also the exam that the urologist does when they remove the tumor (from the bladder using) a camera (inserted) inside the bladder. All of the above factors can help us figure out the (“clinical”) stage, including the muscle invasion.
Transcript has been edited for clarity and conciseness.
For more news on cancer updates, research and education, don’t forget to subscribe to CURE®’s newsletters here.