Sertoli Cell Tumour

A Sertoli cell tumour is a growth that develops from the cells in the testicle that normally support sperm production. These tumours occur almost exclusively in dogs that have an undescended testicle (one that remained in the abdomen or groin rather than descending into the scrotum), though they can occasionally arise in a normally positioned testicle. Some of these tumours produce hormones—particularly oestrogen—which can create effects throughout the body. Owners often notice changes in appearance or behaviour that seem unrelated to the testicles themselves: symmetrical hair loss, darkening of the skin, enlarged nipples, or that other male dogs show unusual interest in their dog. In some cases, the testicle itself may be visibly enlarged or firm, or an owner may be investigating a mass found during routine examination. Other dogs are diagnosed incidentally during investigation of blood changes or urinary signs. This page explores the patterns that can prompt investigation, what is happening at a tissue and hormonal level, the ways these tumours are identified and characterised, and the approaches available once a diagnosis is made.