Q. Recently I took my 4-year-old, spayed, female shorthaired cat to the vet for an allergy shot. She has always had allergies, and our vet had been treating her with shots and prednisone in the past.

Three years ago, another vet said she had a rodent ulcer, which can be caused by excessive licking. The prednisone worked then, but I switched to chlorpheniramine maleate, with the vet's approval because of my concerns about the long-term effects of prednisone. For the last three weeks, however, she has licked herself senseless. She eats really well, has excellent body weight and is active. She always drinks a lot of water.

I got prednisone pills for my cat from the vet. She stopped licking her body but started concentrating on her left paw. The vet examined her mouth and noticed a massive lump on her tongue 98 percent probability it's cancer! I asked if the lump could be from constant irritation and infection, so he gave her antibiotics and an allergy shot, just in case. He told me to keep a close eye on the lump. That is all the information I could get out of him.

Today she is much better, with little to no drooling, and hardly any licking. I'm confused as to what to look for if it is cancer. Should I go to another vet? Watch and wait?

A. I cannot diagnose your cats problem simply from the information in your letter. I can tell you that the two most common problems that have symptoms in which you describe are an eosinophilic granuloma often found in the mouth (they are called rodent ulcers when they are found on the lips) or a type of tumor called a squamous cell carcinoma. It is virtually impossible to tell them apart without performing a biopsy. I would recommend having a biopsy performed as soon as possible. The eosinophilic granuloma can generally be managed with medications, however the carcinoma is generally associated with a grave prognosis. It is not a surprise that your cat seems better with medication because both conditions are associated with infection and inflammation, so a temporary improvement would be expected with either problem.