A broom is a benign tumor, which originates from the connective tissue and thus usually occurs in the skin and the sub skin. We typically see it in the older cat. They are well defined, generally quite firm, but sometimes softer and usually have a round or oval shape. After surgical removal, we typically do not see any recurrence.
Fibrosarcoma is the malignant variant, which occurs regularly in cats. We usually find them in the skin, the underskin, the oral cavity, the nasal cavity, but also elsewhere in the body. They vary in size, but can sometimes become very large. They are irregular, poorly bounded with often a broken parent (ulcerated) skin. They quickly seed out, mostly to the lungs, and rarely to the regional lymph nodes. After surgical removal, one often immediately sees recurrence.