Sertoli Cell Tumour

A Sertoli cell tumour is a growth that arises from the supporting cells inside a testicle. These cells ordinarily help produce sperm; when they form a tumour, they often begin secreting hormones — particularly oestrogen — in amounts that can affect the rest of the body. The tumour itself may cause the testicle to enlarge, change shape, or become firm, though in some cases there are no obvious changes to the testicle at all. Owners most commonly notice changes in coat quality, skin darkening, or behavioural shifts in male dogs, sometimes before realising the testicle itself feels different. These tumours are far more likely to occur in a cryptorchid (undescended) testicle, but close to half arise in normally descended testicles, usually in older dogs. In some cases, the first sign is another dog showing unusual interest, or a routine examination identifying an asymmetry. This page explores what signs may appear, what is happening hormonally and within the testicle, how the condition is investigated through examination and imaging, and the approaches available once a tumour is identified. The aim is to help you understand the pattern your dog may be showing and the shape of the conversations that may follow.