Testicular Cancer in Dogs: Symptoms to Watch For and What to Do Next

Discovering an unusual lump or noticing unexpected changes in your dog can be one of the most unsettling experiences as a pet owner. If you suspect your dog may have testicular cancer, you are not alone — it is one of the most common cancers in intact male dogs, and catching it early can make a tremendous difference in outcomes. This guide will walk you through everything you need to know, from recognizing the warning signs to understanding when it is time to call your veterinarian.

Common Causes

Testicular cancer in dogs does not always have a single, identifiable cause, but veterinary researchers have identified several factors that can significantly increase your dog’s risk. Understanding these risk factors can help you stay vigilant and advocate more effectively for your dog’s health during routine checkups.

The most well-established risk factors include:

• Intact (unneutered) status: Dogs that have not been neutered are the only ones at risk for testicular cancer, since the condition requires the presence of the testicles. Neutering eliminates this risk entirely.
• Age: Testicular tumors are most commonly diagnosed in middle-aged to older dogs, typically those over six years of age. The risk increases steadily as your dog gets older.
• Cryptorchidism: This condition occurs when one or both testicles fail to descend properly into the scrotum and remain in the abdomen or inguinal canal instead. Dogs with retained testicles are significantly more likely — up to 13 times, according to some studies — to develop testicular cancer in the undescended testicle.
• Breed predisposition: Certain breeds, including Boxers, German Shepherds, Weimaraners, and Shetland Sheepdogs, appear to have a higher incidence of testicular tumors, suggesting a possible genetic component.
• Environmental factors: Prolonged exposure to certain chemicals, pesticides, or environmental toxins has been discussed as a potential contributing factor, though the research in this area is still developing.

The three most common types of testicular cancer in dogs are Sertoli cell tumors, seminomas, and interstitial (Leydig) cell tumors. Each type behaves differently, and some are more likely to spread to other parts of the body than others. Sertoli cell tumors are particularly notable because they frequently produce excess estrogen, leading to a distinct set of hormonal symptoms. Seminomas sit in the middle of the spectrum — occasionally malignant, but often slow-growing. Interstitial cell tumors are generally the most benign of the three and rarely spread beyond the testicle itself.

Age plays a meaningful role not just in overall risk but also in which tumor type tends to appear. Interstitial cell tumors are often found incidentally in older dogs during routine exams, while Sertoli cell tumors and seminomas are more likely to produce noticeable clinical signs that bring owners to the clinic. If your dog is approaching his senior years and is still intact, this is a worthwhile conversation to have with your veterinarian at his next annual visit.

From a diagnostic standpoint, identifying the cause and type of tumor typically begins with a hands-on physical examination, followed by scrotal or abdominal ultrasound to assess the size, location, and internal structure of the mass. Bloodwork helps evaluate whether hormone levels are abnormal and whether bone marrow function has been affected. However, a definitive diagnosis — meaning a confirmed tumor type — requires histopathology, which is microscopic examination of the tissue after surgical removal. This is why surgery is almost always both the treatment and the diagnostic endpoint simultaneously.

Symptoms to Watch For

One of the challenges with testicular cancer in dogs is that some cases produce very few obvious symptoms in the early stages, especially if the affected testicle is retained inside the abdomen. However, many dogs do show recognizable signs that something is wrong, and knowing what to look for puts you in a much stronger position to act quickly.

Common symptoms of testicular cancer in dogs include:

• A visible or palpable lump or swelling in one or both testicles, or asymmetry between the two testicles in size or firmness
• Scrotal swelling or changes in texture that were not previously present
• Signs of feminization, particularly associated with Sertoli cell tumors, which can produce estrogen-like hormones — these may include enlarged nipples, a symmetrical hair loss pattern, a pendulous prepuce, or attraction of other male dogs
• Bone marrow suppression, a serious complication of hormone-secreting tumors that can cause lethargy, weakness, pale gums, or increased susceptibility to infection
• Abdominal swelling or discomfort if a retained testicle is involved and has grown significantly
• Changes in behavior or energy levels, such as unusual fatigue or a decreased interest in normal activities
• Infertility in dogs used for breeding, which may be noted before any physical signs appear

It is worth noting that pain is not always present, which means your dog may appear perfectly comfortable even while a tumor is developing. Regular physical examinations at home, as well as annual veterinary checkups, are the best tools you have for early detection.

Symptom Severity at a Glance

Symptom	Risk Level	Action Required
Small, firm lump on one testicle with no other symptoms	Mild	Schedule a vet appointment within 1–2 weeks
Scrotal swelling or noticeable size difference between testicles	Moderate	Call your vet within 24–48 hours
Enlarged nipples, symmetrical hair loss, or feminization signs	Moderate	Call your vet within 24 hours
Lethargy, reduced appetite, or behavioral changes	Moderate	Call your vet within 24 hours
Pale or white gums, unusual bruising, or frequent infections	Serious	Seek veterinary attention the same day
Abdominal swelling or visible discomfort, especially with cryptorchidism	Serious	Seek veterinary attention the same day
Collapse, extreme weakness, or rapid deterioration	Serious	Seek emergency care immediately

Breeds Most at Risk

While testicular cancer can develop in any intact male dog, certain breeds appear in veterinary literature more consistently than others, pointing to a likely genetic predisposition.

Boxers have long been recognized as a breed with elevated cancer risk across multiple tumor types, and testicular tumors are no exception. Their genetic makeup appears to include a reduced ability to suppress abnormal cell growth, making regular monitoring especially important for intact Boxer owners.

German Shepherds show a higher-than-average incidence of cryptorchidism — the retained testicle condition that dramatically increases testicular cancer risk. Because the predisposition to cryptorchidism itself appears to be heritable in this breed, German Shepherds with an undescended testicle face a compounded risk that warrants early veterinary attention.

Shetland Sheepdogs (Shelties) have been identified in several studies as having increased susceptibility to Sertoli cell tumors specifically. This is particularly relevant because Sertoli cell tumors are the type most associated with hormonal complications and bone marrow suppression, making awareness in this breed even more critical.

If your dog belongs to one of these breeds and is intact, proactive conversations with your veterinarian about monitoring schedules — or the option of neutering — are well worth having.

What You Can Do at Home

While there is no home treatment for testicular cancer, there are meaningful steps you can take to support your dog and stay ahead of potential problems. Developing a habit of gentle, regular physical checks is one of the most valuable things any owner of an intact male dog can do.

Once or twice a month, take a few moments during a calm, relaxed time — perhaps when your dog is lying beside you — to gently feel the scrotal area for any changes in size, shape, or firmness. You are not looking to diagnose anything yourself, but rather to notice anything that seems different from the last time you checked. If something feels off, that is your cue to call your vet rather than wait.

Beyond physical monitoring, keeping a log of any behavioral or physical changes you observe can be extremely helpful when you bring your dog in for an appointment. Note things like changes in energy level, appetite, coat quality, or any unusual posturing that might suggest abdominal discomfort. The more information you can provide your veterinarian, the easier it is for them to piece together the full picture.

It is also worth having an honest conversation with your vet about neutering if your dog has not been neutered and you are not using him for breeding. In many cases, neutering is the most straightforward way to eliminate the risk of testicular cancer entirely.

When to See a Vet

You should contact your veterinarian promptly if you notice any lump, swelling, or asymmetry in your dog’s testicles, even if your dog does not seem to be in pain. Early-stage tumors are typically much easier to treat than those that have had time to grow or spread.

Seek veterinary attention without delay if your dog is showing signs of bone marrow suppression — such as lethargy, pale or white gums, unusual bruising, or frequent infections — as these can indicate a hormone-secreting tumor with serious systemic effects. Similarly, if your dog’s abdomen appears swollen or he seems uncomfortable, especially if you know he has an undescended testicle, this warrants an urgent appointment.

Your vet will likely perform a physical examination, recommend bloodwork, and may suggest imaging such as ultrasound to evaluate the extent of any abnormality. A definitive diagnosis typically requires histopathology following surgical removal of the affected testicle.

How Pet Insurance Can Help

Diagnosing and treating testicular cancer can involve imaging, surgery, laboratory testing, and in some cases oncology referrals — costs that can add up quickly and catch pet owners off guard. Having a pet insurance policy in place before a diagnosis is made can help protect both your finances and your ability to say yes to the care your dog needs.

Protective Care: Get a free pet insurance quote and protect your dog today

For times when you need immediate guidance from a licensed veterinarian without leaving home, telehealth services can be a lifesaver.

For more clinical details on canine health, you can refer to the professional guidelines from the Merck Veterinary Manual.

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Finding a potential health concern in your dog is understandably worrying, but the fact that you are looking for information and paying close attention is already a sign of how much you care. Testicular cancer in dogs is often very treatable when caught early, and with a good veterinary team on your side, many dogs go on to live full, healthy lives after treatment. Trust your instincts, stay observant, and never hesitate to reach out to your vet when something does not feel right.