Not all tumors in dogs are bad news. Canine Cutaneous Histiocytoma is a very common benign skin tumor that is seen mostly in young dogs under the age of three years, however it can be seen in older dogs as well. Histiocytoma originates from histiocytes, which are a type of cell. It is usually a firm, roundish, hairless, red and 'angry' looking lump on the skin on any part of the body. It can appear very suddenly and it's appearance can be quite alarming to owners.