Dear Doctor: A cancer medicine for dogs but not cats
Q. Last May my beloved 13-year-old cat was diagnosed with oral squamous cell carcinoma and passed in August. A few months later our shelter’s newsletter told the story of a family whose dog had been diagnosed with the very same thing and, with a prognosis of 8 months, she actually lived 7Ĺ more years with the help of Piroxicam. This blew me away, as this drug was never mentioned for Mickey (and we took him to the best-of-the-best, the University of Missouri’s Veterinary Health Center in Columbia). In doing my own research I get the impression Piroxicam is only for dogs. If so, why isn’t there an equivalent for cats?
Kansas City, Missouri
Dear Ms. LeSage,
A. We are very sorry for your loss. Often, both dogs and cats with cancer receive metronomic chemotherapy — low-dose, relatively inexpensive, daily chemo delivered by mouth at home, usually given for as long as the patient lives. This is different from conventional chemotherapy, which is delivered via injection at 2- to 3-week intervals.
Another difference is that conventional chemo is intended to kill cancerous cells and thereby actually shrink tumors. Metronomic chemo, by contrast, is thought simply to slow or stop the growth of cancerous tumors, largely by depriving them of their blood supply. The idea is to help the patient live with the tumor rather than try to kill it.
Here’s the difference in the treatment of the two species. In dogs, metronomic chemotherapy drugs, which include cyclophosphamide and chlorambucil, are generally combined with a nonsteroidal anti-inflammatory drug, or NSAID (same class as ibuprofen). The NSAIDs, similar to the chemotherapy drugs, are believed to help inhibit cancerous tumors by inhibiting the growth of blood vessels that feed them. They can also potentially help with pain because they have an anti-inflammatory effect. Piroxicam falls into this category.
But while metronomic chemo drugs and NSAIDs are relatively easy to combine in dogs, they are difficult to do in cats because of toxicity issues. Up to 30 percent of cats are apt to experience GI upset in the form of vomiting and diarrhea with NSAIDs, says Tufts veterinary oncologist Carrie Wood, DVM, and also kidney injury and liver toxicity. In addition, Dr. Wood explains, many older cats have kidney disease in the first place — it’s much more prevalent in felines than canines — and NSAIDs only serve to make kidney disease worse.
Because your own cat had cancer in his mouth, medicines that are given in pill form — Piroxicam as well as metronomic chemotherapy drugs — become even less of an option. “It’s hard to give a cat a pill when he has a tumor in his mouth,” Dr. Wood says. “If the tumor is painful, you don’t want to be trying to force more pills in.”