Back on August 12th, I talked a lot about cancer in veterinary patients. I didn’t cover the way we diagnose cancer, though. The process for diagnosing cancer can be quite confusing, so I’d like to take some time today to shed a little light on how we hunt for answers.
We talked about how a mass/tumor/growth is properly termed Neoplasia. Once a mass is discovered, we have to start testing the mass to find out whether it’s benign or malignant, and whether it has stayed put or has spread to other areas of the body, and how aggressive it appears to be.
Step 1 : Obtaining a Sample
In order to learn anything about a mass, we have to be able to observe the microscopic cells that make up the mass. The objective here is to discover, if possible, the tissue in which the mass started to grow. Depending on how we get a sample to observe, we may be able to accomplish the second two steps as well. We can obtain a sample in three ways.
A. Fine needle aspirate.
A needle attached to a syringe is inserted into the mass. The plunger on the syringe is pulled back to create a vacuum that sucks some cells into the needle. The cells in the needle are then gently sprayed onto a microscope slide. We use a special stain to make the cellular structures visible, then observe the sample under the microscope. This method can be performed on-site at the veterinary hospital. In some cases, a general practitioner will send the slides in for a board-certified pathologist to look at. I prefer to have a pathologist verify my observations in most cases.
B. Incisional Biopsy.
A small piece of the mass is cut out and preserved in a special fluid. We send the piece into a lab, where it is sliced into micro-thin layers. These slices are observed under the microscope. This allows a board-certified pathologist to see not only the cells, but how they are arranged, which gives clues about the structure of the mass. The drawback to this technique is that a patient may need anesthesia in order to obtain this type of sample, and we leave the rest of the mass on the patient. If the pathology report comes back as malignant, the patient will need anesthesia again to take the mass off the body. The advantage to knowing what type of malignancy we’re dealing with is that it can tell us the best way to treat the mass. This includes surgical removal or other treatments such as chemo or radiation.
C. Excisional Biopsy.
In this method, the entire mass is removed at one time. Then, the whole mass (or less commonly, a part of it) is then sent in to the lab’s pathologist. As with the incisional biopsy, the pathologist can observe the type of cells and how they are arranged. The advantage here is that we can try to get the whole mass out (leaving nothing behind on the patient) with one trip under anesthesia. However, if we don’t know the tissue type or we’re unsure about the behavior of the mass, the surgery might not get the whole mass out.
When a pathologist looks at cells to determine if a mass is malignant or benign, there is a set of specific criteria to observe in the cells. If enough of these criteria are seen, a mass is called malignant. The criteria have to do with the size, shape, and contents of the cellular structures.
Step 2 : Grading
Once we have a mass identified, and we know the tissue of origin, we have to go through a process called “Grading.” The mass has come from a specific tissue. Hopefully, we know what type of tissue we started with. Looking at the cells may give us that specific answer. However, the cells in a mass are sometimes very different in appearance than the tissue type they started in. How similar the mass cells look to their tissue of origin is the criteria for grading a mass. Higher grades mean that the cells look less and less like the tissue of origin. This is important to know because it can give us clues about how aggressively a mass will behave. It may help us make treatment decisions and shed light on the longterm prognosis for a patient. In most cases, a higher grade tumor is more difficult to treat successfully and has a worse prognosis.
Step 3 : Staging
Masses that are malignant have the potential to spread to other places in the body. That spread, or metastasis, is a very important thing to find as we determine how to treat a patient. Each stage is defined by how far the mass has spread. Lower stages mean the mass has stayed in its immediate area. Higher stages mean the mass has spread to other parts of the body, such as lymph nodes or other organs.
Step 4 : Treatment Plans
Once we know the grade and stage of a mass/cancer, we can develop an individual treatment plan for a patient. Treatment with surgery, chemo, radiation, and/or a vaccine may be used to treat a cancer patient. The grade and stage provide us useful information about the longterm prognosis for cure vs. remission, and how long remission can be expected to last.