Mast cell tumour
A common skin tumour in dogs that can range from a benign lump to an aggressive cancer. Many present as a "boring" skin bump and need biopsy.
Mast cell tumours (MCTs) are one of the most common skin cancers in dogs. They are notorious for variability — some are entirely benign and excised cleanly, others are aggressive and metastatic. Outwardly they often look like a simple lump, sometimes hairless, sometimes red or itchy, sometimes changing in size.
Breeds with higher incidence: Boxer, Bulldog, Labrador, Golden Retriever, Pug, Boston Terrier, Pit Bull. The "Boxer with a lump" stereotype is grounded in reality.
The right approach to any new lump: fine-needle aspirate first. Mast cells are highly distinctive on cytology, so a quick in-clinic aspirate (often the same day as discovery) can confirm or rule out MCT before any decision about surgery.
Treatment depends on grading. Low-grade MCTs are usually cured by surgical removal with wide margins. Higher-grade tumours may need chemotherapy, radiation, or targeted therapy. Localised cases often have good outcomes; metastatic cases require oncology specialist input.
Bottom line: never "watch and see" a new lump on a Boxer or similar predisposed breed. Aspirate first.