Dear Doctor - Dog diagnosed with lymphoma
Do more side effects mean the chemo is working better?
Q My beagle was recently diagnosed with lymphoma. Treatment has been slow, as her white blood cell counts have dropped with each dose of the chemotherapy drug doxyrubicin and they have to keep delaying the next round of the medicine. The last dose almost killed her. But I was wondering, could her sensitivity to the drug be a positive indicator that it is working?
Oil City, Pennsylvania
Dear Ms. Osten,
A First, we are sorry to hear of your dog’s lymphoma, or cancer of the lymph nodes. The reason her white blood cell counts are dropping with each chemotherapy treatment is that chemo kills not only cancer cells but also other rapidly dividing cells in the body, including cells in the bone marrow that make white blood cells.
Fewer white blood cells mean a suppressed immune system, which is why people who get chemotherapy often can’t be visited by family and friends unless they are wearing masks and protective gowns. They are too prone to infection.
Dogs are treated less aggressively with chemo than people — the aim is to extend their quality of life for as long as possible, not their quantity of life for as long as possible. Still, “we see some bone marrow suppression in dogs receiving chemo,” says Tufts veterinary oncologist Kristine Burgess, DVM. “It’s not usually low enough that the dog has to be hospitalized, like some people do, but we often have to give more time between chemo treatments to let the white blood cell count increase again so the dog can withstand possible infection that might come along.”
It’s not usually beagles who are so sensitive to chemo, Dr. Burgess remarks. Certain breeds of dogs (for example, Australian shepherds and collies, including border collies) can be at increased risk for side effects from chemotherapy. Their sensitivity to chemotherapy drugs is related to a genetic mutation that makes them inherently very sensitive to chemo’s effects, although dogs of other breeds, like yours, may be affected, too.
Unfortunately, the doctor says, “when you give chemo to a dog, you don’t know what the reaction is going to be until you administer it. You have to look in the rear-view mirror and increase or decrease the dose based on what already happened.”
As for whether sensitivity to a chemo drug means it is working better in the dog, Dr. Burgess says that “it would be great if it were that simple.” But it’s not. Reactions to chemotherapy agents do not predict their effectiveness.
That said, the odds are with you for now. The remission rate with chemo for dogs diagnosed with lymphoma often falls in the 70 to 90 percent range. All evidence of the disease is gone, and the dog feels good for an average of eight to 12 months.
Most dogs will eventually come out of remission. It can be re-induced with further chemotherapy treatments, although the length of response varies greatly between dogs.