Diagnosis
Because of the unique characteristics of FISS, diagnosing it can be difficult compared to other cancers.
Generally, cats with FISS present with few clinical symptoms except for a subcutaneous mass near common injection areas (shoulders, hips, legs, tail). If you notice a lump or mass on your cat, you should follow the 3-2-1 rule to decide whether your cat should be seen by a vet or not. If any of the following are true, it’s time to the visit the vet:
The mass persists for more than three months
The mass is larger than two centimeters
The mass increases in size over one month
If you’ve determined your cat should see a vet, they will usually start by performing a fine-needle aspiration (FNA). This is the least invasive and costly of the diagnostic procedures available. However, FNAs are not always successful in diagnosing FISS. These types of tumors don’t readily exfoliate their cells and a needle aspirate may not collect any cancerous cells despite them being present. This was the case with Momo. His tumor was biopsied via FNA the day it appeared and the results showed inconclusive cells, cells “consistent with a cyst,” and osteoclasts. If your vet suspects the tumor could be an FISS, I highly recommend opting for a more aggressive and definitive diagnostic procedure. However, FNAs are quick and easy and may help rule out other causes. An incisional biopsy may also be performed, which includes surgically removing a portion of the mass for analysis. It is important that any biopsy tracts are within the area that may be excised are part of tumor removal since neoplastic/cancerous cells can be spread via biopsy.
Ultimately, the gold standard for diagnosis is surgical excision. This includes removing the entire tumor with wide margins and submitting the tissue for analysis. In my opinion, this is the best mode of diagnosis since you get to kill two birds with one stone (biopsy and tumor removal in one procedure) and the bulk of the disease is removed ASAP.
Due to the incredibly aggressive nature of FISS, if your vet suspects FISS things may begin moving extremely fast. When I brought Momo to the vet I did not expect for him to undergo a major surgery, but our vet emphasized that acting quickly and aggressively was vital. It’s terrifying but you have to trust your vet in these scenarios. Your cat’s prognosis improves the earlier you are able to remove the tumor. Additionally, the longer you wait, the greater chance tissue within the tumor has necrosed, which can be uncomfortable for your cat.
