Yes, dogs can get testicular cancer, and it’s actually the most common type of reproductive tumor in intact (unneutered) male dogs. Testicular tumors account for up to 90% of all cancers in the male reproductive system. Prevalence estimates vary, with recent studies placing the rate between 5% and 27% of intact males, depending on the population studied. The good news: most testicular tumors in dogs are treatable, and surgical removal is curative in the vast majority of cases.
Types of Testicular Tumors in Dogs
Three types of testicular tumors make up nearly all cases in dogs. Seminomas arise from the cells that produce sperm. Sertoli cell tumors develop in the cells that support and nourish developing sperm. Interstitial (Leydig) cell tumors grow from the cells that produce testosterone. It’s not uncommon for a dog to have more than one type at the same time, or even to have tumors in both testicles.
These tumor types behave differently. Interstitial cell tumors are almost always benign and rarely cause problems beyond the testicle itself. Seminomas and Sertoli cell tumors carry a higher risk of spreading, though metastasis is still relatively uncommon overall.
Sertoli Cell Tumors and Hormonal Effects
Sertoli cell tumors deserve special attention because they can produce estrogen, which causes a recognizable set of symptoms sometimes called “feminization syndrome.” Dogs with estrogen-producing tumors may develop symmetrical hair loss (especially along the flanks and belly), darkened skin, enlarged nipples, a swollen prostate, and behavioral changes like reduced aggression or increased attraction from other male dogs.
In severe cases, excess estrogen suppresses the bone marrow, which can lead to dangerously low blood cell counts. This complication, called estrogen toxicity, is the most life-threatening aspect of Sertoli cell tumors and requires urgent veterinary treatment.
Cryptorchidism Is the Biggest Risk Factor
Cryptorchidism, a condition where one or both testicles fail to descend into the scrotum, dramatically increases a dog’s cancer risk. Studies show cryptorchid dogs are 9 to 14 times more likely to develop testicular cancer than dogs whose testicles descended normally. The risk is even more striking when broken down by tumor type: retained testicles face a 23-times greater risk of Sertoli cell tumors and a 16-times greater risk of seminomas compared to normally positioned testicles.
The retained testicle sits in the abdomen or inguinal canal, where it’s exposed to higher body temperatures than a scrotal testicle. This abnormal environment is thought to promote tumor development. Because the retained testicle is hidden inside the body, tumors there can grow undetected for longer, making regular veterinary checkups especially important for cryptorchid dogs.
Breeds With Higher Risk
Certain breeds show a predisposition to specific tumor types. Shetland Sheepdogs and Collies are more prone to Sertoli cell tumors, while Norwegian Elkhounds have a higher incidence of seminomas. Breeds with elevated rates of cryptorchidism, such as Yorkshire Terriers, Pomeranians, and Chihuahuas, also face greater overall testicular cancer risk simply because undescended testicles are more common in those breeds.
Age is another factor. Testicular tumors are most frequently diagnosed in middle-aged to older dogs, typically between 7 and 12 years old.
Signs You Might Notice at Home
The most obvious sign is a lump or swelling in one testicle, or a noticeable difference in size between the two testicles. Some tumors grow slowly and remain small, while others can become quite large. Beyond the visible swelling, watch for:
- Hair loss on both sides of the body, particularly along the flanks, belly, or chest
- Skin darkening in areas where hair has thinned
- Enlarged nipples or mammary tissue
- Swelling near the prepuce (the skin covering the penis), which can indicate a prostate problem driven by excess estrogen
- Lethargy or weakness, which may signal bone marrow suppression in advanced cases
Some testicular tumors produce no obvious external symptoms at all, especially interstitial cell tumors. These are often discovered incidentally during a routine exam or an unrelated procedure.
How Testicular Cancer Is Diagnosed
A veterinarian can often detect a testicular mass through physical examination alone, but ultrasound provides much finer detail. It can reveal lesions too small or too deep to feel by hand, and it helps characterize the tumor’s size, location, and structure. However, ultrasound alone can’t determine whether a mass is cancerous or benign.
To confirm the diagnosis, your vet may perform a fine-needle aspiration, where a thin needle draws a small sample of cells from the mass for examination under a microscope. In many cases, definitive diagnosis happens after surgery, when the removed testicle is sent to a pathologist for a full tissue analysis. If there’s concern the cancer may have spread, chest X-rays and abdominal imaging can check for tumors in the lymph nodes or other organs.
Treatment and Prognosis
Surgical removal of the affected testicle (orchiectomy) is the standard treatment, and for the vast majority of dogs, it’s curative. Most veterinarians recommend removing both testicles even if only one appears affected, since the remaining testicle is still at risk. If a dog has a retained testicle with a tumor, the surgery is slightly more involved because the vet needs to locate and remove the testicle from within the abdomen.
For the small percentage of cases where cancer has already spread at the time of diagnosis, chemotherapy may be recommended after surgery. Cisplatin-based protocols, similar to those used in human testicular cancer, have been used in dogs with aggressive tumors. Prognosis for metastatic testicular cancer is less favorable, but the overall metastasis rate is low enough that most dogs are cured by surgery alone.
What Recovery Looks Like
After surgery, your dog will likely be groggy for the first 24 to 48 hours as the anesthesia wears off. Offer a small meal a few hours after arriving home rather than a full portion, since nausea after general anesthesia is common. An Elizabethan collar or recovery suit prevents your dog from licking or chewing the incision, which is one of the most important things you can manage during healing.
A small amount of blood seeping from the incision in the first 24 hours is normal. Contact your vet if you notice continuous bleeding, excessive swelling, redness, discharge, or an unpleasant odor at the surgical site. Stitches are typically removed 7 to 14 days after surgery. Most dogs return to their normal behavior within a few days, though you’ll want to limit vigorous activity until the incision has fully healed.
If the tumor was producing excess estrogen, hormonal symptoms like hair loss and skin changes typically reverse within a few weeks to months after surgery. Bone marrow suppression, if present, also begins to recover once the estrogen source is removed, though severe cases may need supportive care during that period.
Does Neutering Prevent Testicular Cancer?
Neutering eliminates testicular cancer risk entirely, since it removes the testicles. This is one of the most straightforward cancer prevention measures in veterinary medicine. For cryptorchid dogs especially, early neutering is strongly recommended because of the dramatically elevated cancer risk in retained testicles.
The ideal timing of neutering is more nuanced than it once seemed. A large study covering 35 breeds found that for most breeds, neutering can be performed at any age without significantly increasing the risk of joint disorders or other cancers. But certain breeds benefit from delayed neutering: Golden Retrievers and Border Collies do better when neutering is delayed past one year, Boxers past two years, and Irish Wolfhounds past two years for males. A few breeds, like Boston Terriers and Shih Tzus, actually showed increased rates of other cancers with neutering, making the decision more complex. The best approach depends on your dog’s breed, size, and individual health profile.