Testicular Tumours

Testicular tumours are abnormal growths that develop in one or both testicles of intact male dogs. They arise when cells in the testicular tissue begin to multiply in an uncontrolled way, forming a mass that can vary in size and behaviour. Some testicular tumours grow slowly and remain contained within the testicle, while others can produce hormones that affect behaviour, coat quality, or other parts of the body. Owners often notice a change in the size, shape, or firmness of one testicle, or observe that the two testicles no longer feel symmetrical. In some cases, the first signs are not related to the testicles themselves—these can include hair loss, skin changes, behavioural shifts, or changes in the way other dogs respond to the affected animal. Occasionally, a testicular mass is found during a routine examination when no outward signs have been noticed. This page explores what signs may be observed, what processes lead to different types of testicular tumour, how they are investigated, and what approaches exist once a tumour is identified. The goal is to help orient your understanding of what may be happening and what the shape of the conversation with your veterinary team might look like.