Testicular Cancer in Dogs

Testicular cancer in dogs usually refers to tumors that develop in one or both testicles. The three main types are Sertoli cell tumors, seminomas, and interstitial cell tumors. These tumors are seen most often in older, intact male dogs, especially if one or both testicles never descended into the scrotum. A retained testicle, called cryptorchidism, raises the risk of cancer and also increases the risk of torsion, which is painful and urgent.

Many testicular tumors stay localized, and some are found during a routine exam before a dog seems sick. That is one reason early evaluation matters. Dogs may have a firm lump, one testicle that looks larger than the other, or a swollen scrotum. Some tumors, especially Sertoli cell tumors, can make hormones that cause feminizing changes such as hair loss, enlarged mammary tissue, a pendulous prepuce, or attraction from other male dogs.

The good news is that many dogs do well when the problem is found early and treated with surgery. In many cases, neuter surgery removes the tumor completely. If your dog has a retained testicle, signs of hormone imbalance, or any new scrotal swelling, your vet may recommend imaging and lab work before surgery so the care plan matches your dog’s age, overall health, and cancer risk.

Diagnosis starts with a hands-on exam. Your vet will feel both testicles, check whether one is missing from the scrotum, and look for signs of feminization or other illness. Basic testing often includes bloodwork and a urinalysis, especially in older dogs or dogs with hormone-related changes. If your dog seems anemic, weak, or systemically unwell, those findings can affect how quickly surgery should happen and what supportive care is needed first.

Imaging may include scrotal ultrasound, abdominal ultrasound, and chest X-rays. These tests help your vet look for a retained testicle, evaluate nearby lymph nodes, and check for evidence of spread. Metastasis is not common with many testicular tumors, but it can happen, so staging is more important when a retained testicle is involved, when the mass is large, or when your dog has weight loss, appetite changes, or other concerning signs.

A final diagnosis usually comes from pathology after surgical removal of the affected testicle or both testicles. That report identifies the tumor type and whether the tissue looks benign or malignant. In breeding dogs, your vet may discuss fine-needle sampling or biopsy in select cases, but surgery is still the most common path to both diagnosis and treatment.

There is no single known cause of testicular cancer in dogs. Like many cancers, it likely develops from a mix of age, genetics, hormone influences, and chance cellular changes over time. What is clear is that intact male dogs are at risk because the testicular tissue remains in place, and risk rises with age.

Cryptorchidism is the most important known risk factor. Dogs with a retained testicle have a much higher chance of developing testicular tumors than dogs whose testicles descended normally. Retained testicles are also at risk for torsion. Because cryptorchidism has a hereditary basis, affected dogs should not be used for breeding, and your vet will usually recommend surgical removal of both testicles.

Breed predispositions have been reported, including Boxers, German Shepherds, Afghan Hounds, Weimaraners, Shetland Sheepdogs, Collies, and Maltese. Tumor type also matters. Sertoli cell tumors and seminomas are more associated with retained testicles, while interstitial cell tumors are often benign and less likely to spread. Even so, any new testicular change deserves an exam because appearance alone cannot confirm the tumor type.

The most effective prevention step is timely neuter planning with your vet. Removing the testicles eliminates the tissue where these tumors develop. For dogs with cryptorchidism, surgery is especially important because retained testicles carry a much higher cancer risk and can also twist. Dogs with retained testicles should not be bred because the condition is inherited.

Prevention is not only about surgery timing. Routine wellness exams matter because many dogs show few signs early on. If your dog is intact, monthly at-home checks for symmetry, swelling, or firmness can help you catch changes sooner. Bring up any new lump, scrotal enlargement, or hormone-related skin and coat changes right away.

Some large-breed dogs may have individualized neuter timing discussions for orthopedic or other health reasons. That decision should be made with your vet based on breed, age, lifestyle, and overall risk. Even when neuter is delayed for a medical reason, regular monitoring of the testicles becomes more important, not less.

Many dogs have a favorable outlook after surgery, especially when the tumor is found early and has not spread. Interstitial cell tumors are usually benign. Seminomas and Sertoli cell tumors can be malignant, but metastasis is still relatively uncommon in many cases. When the disease is confined to the testicle, neuter surgery is often curative.

Recovery from surgery is similar to other neuter procedures, though abdominal cryptorchid surgery can involve a longer recovery than a routine scrotal neuter. Most dogs need activity restriction, incision monitoring, and an e-collar or recovery suit to prevent licking. Your vet may recommend a recheck and will review the pathology report to decide whether more testing is needed.

Prognosis becomes more guarded if the tumor has spread or if a Sertoli cell tumor has caused significant estrogen-related bone marrow suppression. Those dogs may need more intensive monitoring and supportive care. Even then, there are still treatment options, and your vet can help you weigh conservative, standard, and advanced paths based on your dog’s comfort, overall health, and your goals.