My Cat Has Cancer: Staging and Grading the Tumors
AJ Debiasse, a veterinary technician in Stroudsburg, PA, contributed to this article.
Few things are as devastating as learning that your beloved cat has cancer. Yet, despite the emotional rollercoaster, you must be strong and make the best possible decisions for your beloved pet. Two of the most important concepts you need to understand when discussing cancer with your family veterinarian, a surgeon or an oncologist (a cancer specialist) are "grading" and "staging" of the cancer.
Staging a tumor
Staging is a way to find out, with as little doubt as possible, if a tumor has spread anywhere in the body. Staging is determined by your family veterinarian, a surgeon or an oncologist; it’s based on several factors:
- From experience, veterinarians know that some tumors are more likely to spread than others. Benign tumors don’t spread. Some cancerous tumors rarely spread (e.g., fibrosarcoma). Other cancers spread quickly (e.g., bone cancer).
- Chest X-rays are an easy way to evaluate spreading to the lungs. A fancier test, that can show much smaller masses, is a cat scan of the chest.
- Sometimes, tumors in the belly (e.g., hemangiosarcoma in the spleen) tend to spread to the liver, so an ultrasound is often recommended to “explore” the entire area.
- Some tumors (e.g., oral cancer) first spread to a nearby lymph node, which can be suspected (but never proven) by doing a thorough physical exam on your cat.
- Other tumors (e.g., malignant melanoma) most often spread to the lungs, which act as a filter for tiny cancer cells.
Grading a tumor
The grade describes how aggressive a tumor is, including how likely it is to spread. Grading is judged by a pathologist, after analyzing a tumor sample under the microscope. There are different systems to grade a tumor. Simply said, there are three basic grades:
- Grade 1 describes a mass that is cancerous but usually localized, and not very likely to be metastatic or metastasize (i.e., spread to other organs).
- Grade 2 is a tumor that is more aggressive; it may or may not spread.
- Grade 3 is the most aggressive type with a high likelihood of spreading.
Other tumors are graded differently:
- “Well Differentiated” are better
- “Moderately Differentiated” or “Poorly Differentiated” are worse
Others are called:
- Low grade
- Medium grade
- High grade.
Your veterinarian will explain based on your cat’s situation.
Practically, the most effective way to grade a tumor is to take a biopsy, or even remove it all, and send it out for analysis under the microscope. A biopsy is very different from a needle sample of a tumor (fine-needle aspirate), where cells are drawn out with a needle and placed on a slide to be examined under a microscope. This test can be helpful but does not provide a grade for the tumor. We need a larger sample of the mass to achieve that.
Grading and staging tumors are inter-related
Interestingly, there is a relationship between the grade and the stage of a tumor. For example, a grade 1 tumor is the least likely to spread to other organs, with a better survival rate. On the opposite end, a grade 3 tumor has a high risk of spreading, and therefore the outcome will logically be worse.