Mast Cell Tumor Is the Most Common Canine Skin Cancer

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Q: My Lab mix has a mast cell tumor. What can you tell me about this condition?

A: A mast cell tumor, or MCT, is the most common form of skin cancer in dogs. Mast cells are white blood cells designed to fight parasites and allergies. It’s not clear why some of these immune cells develop into tumors.

MCTs vary widely in appearance, although many are solitary, hairless, raised, pink masses that don’t itch or hurt. Usually they are in the skin, but sometimes they develop in the subcutaneous space between the skin and muscle or inside the body.

The typical patient is an 8- or 9-year-old mixed-breed dog, but risk is also high among some purebreds, including Labrador retrievers, golden retrievers, and dogs with flat faces, such as Boston terriers, boxers, English bulldogs, and pugs.

The diagnosis is often made by inserting a fine needle into the mass, withdrawing some cells, and examining them under a microscope. Granules within mast cells usually stain purple.

Once it’s removed, a mast cell tumor should be graded by the pathologist who evaluates the biopsy sample. Low-grade tumors are less of a problem than high-grade tumors, which are aggressive, often spread elsewhere in the body, and may shorten the dog’s life.

The most common treatment is surgical removal of the MCT, which is often curative, especially for low-grade tumors that are completely excised.

Other treatment options include medications given orally or injected into the tumor if surgery isn’t feasible, radiation to shrink the tumor before surgery or when complete surgical removal isn’t possible, and chemotherapy to prevent or treat the spread of a high-grade MCT.

Dogs that develop a mast cell tumor are at increased risk of forming more in the future, so monitor your pet’s skin regularly and report any new lumps or bumps to your veterinarian immediately.

Q: We just bought a houseplant called a Norfolk Island pine, and our rabbit, Oreo, is nibbling the wood. Will it hurt him? Since he likes to chew, should we cut branches from our outdoor trees for him to nibble?

A: It’s important for rabbits to chew because their teeth grow continuously, and chewing helps keep them ground down to a healthy level. Pine is safe to chew, though Oreo may damage your new plant.

Consider offering him pine branches from your outdoor pine trees, pine firewood, pine cones, or a piece of untreated pine lumber. Apple, willow, poplar, and aspen branches also are fine.

Oreo should not be permitted to chew fresh branches from single-stone fruit trees, such as peach, apricot, or plum. However, after they’ve been cut and dried for at least a month, these branches are safe to chew.

An old wicker basket, a cardboard box full of hay, paper towel rolls, and toilet paper rolls stuffed with hay also make good chew toys.

Be sure to offer Oreo plenty of fresh grass hay daily. Hay, rather than hay cubes, is preferred, because the long strands help grind down the teeth.

Offer Oreo unlimited timothy, Bermuda, brome, oat, and orchard grass hay. Don’t feed alfalfa, because its protein and calorie content are too high for adult rabbits.