Mast cell tumors (MCTs) are a common skin growth in dogs and cats, originating from immune cells abundant in the skin. Recognizing these growths can be challenging for pet owners due to their varied appearance, making it important to know when to seek veterinary attention.
The Varied Appearance of Mast Cell Tumors
Mast cell tumors are often called “great imitators” due to their diverse visual characteristics. They vary considerably in size, from small bumps to large masses. Shapes can differ widely, appearing as round, irregular, flat, or cauliflower-like growths. Some may present as firm plaques, which are hard, flattened areas on the skin.
Their color is equally variable, appearing pink, red, skin-colored, or dark; they may also be ulcerated, bruised, or swollen. When touched, their texture can be soft, firm, rubbery, or fluid-filled, and they might be mobile under the skin or fixed to deeper tissues. Some may also show hair loss or develop open sores and crusting on their surface.
These tumors can develop anywhere, though often on the trunk, limbs, head, and neck. A distinctive feature is their tendency to fluctuate in size, spontaneously getting larger or smaller, sometimes daily. This is due to histamine release from mast cells within the tumor. Size changes can occur after agitation, leading to localized swelling.
Why Visual Identification Isn’t Enough
The variable appearance of mast cell tumors means visual inspection alone is insufficient for diagnosis. Many other benign or malignant skin growths can mimic a mast cell tumor, making distinction impossible without further testing. For instance, a mast cell tumor might resemble a fatty tumor (lipoma), a fluid-filled cyst, a wart, a histiocytoma, or an abscess.
Even experienced veterinarians cannot definitively diagnose a mast cell tumor by looking or feeling. The tumor’s internal cellular structure and behavior, which determine its nature and potential for spread, are not visible. Relying solely on appearance could lead to misdiagnosis, potentially delaying appropriate intervention. Accurate identification necessitates specific diagnostic procedures examining the growth’s cellular composition.
Next Steps: What to Do If You Find a Suspect Lump
If a lump or bump is discovered on your pet, schedule an immediate veterinary consultation. While many lumps are benign, any new or changing growth warrants professional evaluation to rule out serious conditions like mast cell tumors. The veterinarian will conduct a thorough physical examination, carefully assessing the lump and checking for other masses.
To determine the lump’s nature, the veterinarian will likely recommend diagnostic tests, most commonly a fine needle aspiration (FNA) or a biopsy. An FNA involves using a small needle to collect cells from the lump, which are then examined under a microscope by a pathologist. This quick procedure often provides enough information to identify mast cells due to their distinct appearance. If FNA is inconclusive or if more information about the tumor’s aggressiveness (grade) is needed, a biopsy may be performed, removing a larger tissue sample for detailed microscopic evaluation. These tests are essential for accurate diagnosis and to guide any necessary treatment plan.