Let's share a case about a cat named Black Sugar, a two-year-old large black cat. Earlier this year, Black Sugar was brought in for a lump found on his back—discovered incidentally by touch without knowing how long it had been there. He had no history of injury but was vaccinated for rabies last year.
Veterinarians get very concerned when they feel lumps near a cat's shoulder blades because of past difficult experiences with such tumors. These lumps could be benign or malignant, originated from various cell types such as round cells, epithelial, or stromal cells, and their rates of invasion vary. It's also possible they aren't tumors at all but inflammations or infections that resolve with treatment. Different lumps require different treatments, so proper sampling is crucial to decide the best course of action. If owners opt out of sampling, treatment is based on the vet's experience and luck, risking missed optimal treatment windows and more complicated, dangerous, or costly interventions later.
In Black Sugar's case, the lump's location was suitable for a "Tru-cut" biopsy, a type of core needle biopsy that collects a strip of tissue through a small incision, preserving tissue structure with minimal harm. The biopsy result showed the lump wasn't a tumor but panniculitis—an inflammation of the subcutaneous fat layer. Both the vet and owner were relieved to avoid extensive surgery.
The Importance of Sampling
Sampling applies not only to lumps but also to cases like ear inflammation, chronic nasal discharge, or persistent diarrhea, and when disease treatment stalls. Although it adds cost and possibly anesthesia risk, proper sampling is invaluable in reaching accurate diagnoses and effective treatment plans. Owners are encouraged to discuss with their vets and choose sampling when necessary.
Understanding Feline Injection-Site Sarcoma (FISS)
Following up on Black Sugar's case, it's important to learn about FISS, a serious condition in cats that can develop at vaccine injection sites. Sometimes, even after a tumor seems fully removed and the wound heals, the sarcoma can regrow aggressively from underneath without fully curative treatment options.
It's normal for small lumps to form after vaccination due to the immune response; many disappear quickly, while some cause notable inflammation forming lumps like Black Sugar's. How to tell if a lump is abnormal? The veterinary community promotes the "3-2-1 rule" for vigilance post-vaccination:
- If the lump persists for 3 months post-injection.
- If the lump is larger than 2 centimeters in diameter.
- If the lump is still growing 1 month after vaccination.
If any of these criteria are met, it's recommended to sample the lump promptly to rule out or confirm FISS and enable early intervention.
Recommended Injection Sites for Cats
To help monitor and manage potential risks, vets suggest injecting vaccines at different body locations:
- Rabies vaccine: right rear leg (Rabies Ⓡ)
- Feline leukemia vaccine: left rear leg (FeLV Ⓛ)
- Other vaccines: right front leg
- Not recommended: neck or rump areas for injections
- Some also recommend abdominal side injections to facilitate future surgery if needed
Ultimately, owners should always use the 3-2-1 rule after every vaccination to keep an eye on the injection site and seek vet advice if abnormalities arise.
