Lumps are a common finding in many older rats, and making a decision on surgical removal or benign neglect can be difficult sometimes. Many owners will be hesitant to go ahead with surgery due to the cost, the age of the rat, or the risk. A helpful thing to do would be to get some idea of what the lump consists of, which will affect the prognosis with or without surgical removal. Many softer, easily mobile subcutaneous lumps in older, overweight rats will be lipomas, which can safely be left in the rat as long as they are not too large and easily traumatized. Harder masses with knobbly edges that are more adherent to the underlying tissue are often more sinister, especially if they occur along the mammary chain. Fine needle aspirates of the mass are often a good place to start, and will give the clinician an idea of whether to advise the owner to observe the mass, or to start planning for surgery.

Concurrent diseases must also be taken into consideration, as many older rats will also suffer from chronic respiratory disease. Mammary tumours will often be under hormonal control, which means that recurrence is likely if the patient is an intact female or has a pituitary prolactinoma, in which case spaying (for the intact female) or cabergoline will be useful as an adjunct treatment to reduce the risk of recurrence. All these factors must also be considered along with the rat’s age, and many clients do prefer to allow the rat to live out the rest of his or her lifespan without surgical intervention.