Q: Beau, our 1-year-old dachshund, had a small, round, pink mass on his ear. Scheduling an appointment with his veterinarian took longer than usual, and just before the appointment, the mass disappeared, so we canceled. What was the mass? A: It sounds like Beau may have had a histiocytoma, a common skin tumor that usually disappears without treatment. Histiocytomas generally form on dogs under 3 years of age on the front half of the body, often the head. Typically, they are round, raised, dome-shaped, hairless, firm pink masses less than an inch in diameter. The most commonly affected dogs are dachshunds and boxers, although Labrador retrievers, Staffordshire terriers, and other breeds also develop them. The immune system usually attacks these benign tumors, making them spontaneously regress within three months of their appearance. Histiocytomas that don’t disappear in that time and those that cause discomfort or become infected should be removed …