Lump on Your Dog's Testicle or Genital Area

Name: Lump on Your Dog's Testicle or Genital Area
Creator: Dr. Zubair Khalid

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-10-03

A dog lump on the testicle is a common finding in older unneutered males, and in most cases it turns out to be a tumor. Testicular tumors are the second most common tumor type in male dogs, behind only skin tumors [1]. Because of that, any new lump in the scrotum or genital area deserves a veterinary exam instead of a wait-and-see approach.

This article is educational and is not a substitute for veterinary diagnosis or treatment.

Quick Answer

A painless swelling or firm bump on one or both testicles in an intact male dog is most often a testicular tumor, and these tumors are the most common cancer of the male reproductive tract in dogs [1].
The three most frequent types are seminomas, Sertoli cell tumors, and interstitial (Leydig) cell tumors [1].
Testicles that never descended into the scrotum (cryptorchidism) carry a higher risk of tumor development, so a lump may be hidden inside the abdomen instead of visible in the scrotum [1].
Neutering removes the source of the problem and is both the standard treatment for most testicular lumps and the way to prevent them [2].
Diagnosis usually starts with a hands-on exam and ultrasound, and a definitive answer comes from laboratory analysis of the removed tissue [3][4].

What You Are Seeing and What Is Normal

The scrotum is the pouch of skin outside the abdomen that holds the testicles. Testicles need that cooler location because normal body temperature is too high for sperm to develop properly [2]. In a healthy intact male, both testicles should sit in the scrotum, feel similar in size and firmness, and move freely.

Normal testicles are smooth and roughly symmetrical. What owners often notice first is a change on one side only. One testicle may feel larger, firmer, or heavier than the other. Sometimes the whole scrotum looks swollen. Other times there is a distinct pea-sized or marble-sized bump on the surface of the testicle itself.

Some lumps cause no obvious discomfort. Your dog may eat, play, and behave normally while a tumor grows quietly. That is one reason these lumps are easy to miss until they are fairly large.

It also helps to know what is not a testicular lump. A swelling in the scrotal area can come from a scrotal hernia, where abdominal contents push into the scrotum. In one review of 21 dogs with scrotal hernias, 15 were intact and 6 had already been castrated, and scrotal swelling was seen on examination in 20 of them [5]. So a scrotal bulge is not automatically a tumor, and it is not automatically ruled out by neutering.

Main Causes of a Dog Lump on the Testicle

Testicular Tumors

Testicular tumors occur more frequently in dogs than in any other animal species [1]. The cause is not fully understood, but the position of the testicle matters. Testicles that stay inside the abdomen instead of descending into the scrotum are more likely to develop tumors [1].

The three most common types behave differently:

Seminomas tend to be firm and can grow large.
Sertoli cell tumors can produce estrogen, which sometimes causes feminizing signs such as a pendulous prepuce or symmetrical hair loss.
Interstitial (Leydig) cell tumors are often small and may be found incidentally.

More than one tumor type can appear in the same testicle. In a review of 326 cases of testicular tumors in dogs, 27 (8.28%) had multiple tumors within a single testicle, and the most common pairing was seminoma with interstitial cell tumor [1].

Other Causes

Not every lump is cancer. Inflammation of the testicle (orchitis) is one of the more common testicular diseases in dogs, along with degeneration of the sperm-producing tissue, cryptorchidism, and testicular atrophy [3]. A chronic, quiet form of orchitis can exist without obvious signs and is recognized as a cause of infertility in male dogs [6].

Scrotal hernia is another possibility, as noted above [5]. A transmissible venereal tumor can also affect the genital area, though it is more often seen on the external genitalia than inside the testicle itself [7].

Cause	Typical clues	How urgent
Testicular tumor	Firm, painless swelling on one testicle, often in an older intact male	See a vet within days
Cryptorchid tumor	No testicle in one side of the scrotum, or an abdominal mass	See a vet promptly
Orchitis (inflammation)	Painful, warm, swollen testicle, sometimes with lethargy	Same-day visit
Scrotal hernia	Soft scrotal swelling, sometimes vomiting or not eating	Emergency if vomiting
Transmissible venereal tumor	Cauliflower-like mass on the genitalia, often with discharge	See a vet within days

Red Flags That Make It an Emergency

Most testicular lumps are not emergencies on their own. Some situations are.

Go to an emergency clinic now if your dog has a scrotal swelling along with vomiting, retching, or a hard, painful abdomen. In the scrotal hernia review, all three dogs that needed part of their intestine removed had been vomiting [5]. That pattern suggests bowel is trapped, which is a surgical emergency.

Other reasons to seek care the same day:

The scrotum is suddenly much larger, red, or hot to the touch.
Your dog cries out or snaps when the area is touched.
Your dog is straining to urinate or cannot urinate.
There is bleeding or an open wound on the scrotum.
Your dog is lethargic, not eating, or has a fever.

A firm, painless lump that has been there for weeks is not an emergency, but it should still be checked soon. Testicular tumors can spread. Reported cases show aggressive behavior and metastatic spread in the malignant forms of these tumors [8].

What You Can Safely Do at Home While You Wait

You cannot diagnose or treat this at home, but you can gather useful information and keep your dog comfortable.

Look without squeezing. Gently compare both sides with flat fingers. Do not press hard or try to pop anything.
Take photos with a ruler or a coin next to the lump so you can show change over time.
Note the date you first saw it and whether it has grown.
Check for other lumps anywhere on the body. If you find skin lumps too, our guide to Dog Skin Bumps and Lumps: When to See the Vet can help you sort out what needs attention.
Keep a simple log of appetite, energy, drinking, urination, and any vomiting.
Do not apply human creams, antibiotics, or wraps to the scrotum.
Do not give any medication without asking your veterinarian. Doses depend on your dog's weight and health, and your vet will calculate them.
Prevent breeding and keep your dog away from females in heat until your vet has evaluated the lump.

If your dog keeps licking or chewing at the area, a cone can prevent self-trauma while you wait for your appointment.

What Your Veterinarian Will Check and Test

The Physical Exam

Your vet will start by feeling both testicles and the scrotum, checking size, symmetry, and whether both testicles are present in the scrotum. A missing testicle raises the possibility of a retained testicle and a higher tumor risk [1]. The exam also includes a rectal palpation to check the prostate, since testosterone supports normal prostate function and prostate problems often travel with testicular disease [2].

Imaging

Ultrasound is a core part of the reproductive exam. It is safe, easy to perform, and minimally invasive, which is why it is used so widely for testicular conditions [3]. Standard B-mode ultrasound shows the size, shape, and texture of the testicle. Doppler techniques add information about blood flow, and newer microvascular flow imaging can show fine vessel patterns that older Doppler methods miss [3].

Different tumor types can look similar on basic ultrasound, so imaging alone does not always tell you which tumor you are dealing with [4]. Blood flow patterns do differ between tumor types, and one study found that Sertoli cell tumors had higher flow readings in the testicular and pampiniform vessels than other tumors [4]. Contrast-enhanced ultrasound was highly effective at detecting tumors, though it did not reliably separate one type from another [4].

Blood Work and Hormone Testing

Testicular function can be assessed with semen evaluation and hormone tests, and testicle examination and measurement help evaluate fertility and reveal reproductive disease [2]. If a Sertoli cell tumor is suspected, your vet may check estrogen levels because these tumors can produce it.

Tissue Analysis

The only way to know for certain what a lump is, is to look at the tissue under a microscope. That usually happens after the testicle is removed. In one study of 68 testicular tumor samples, 39.7% were Leydig cell tumors, 33.8% were seminomas, and 26.4% were Sertoli cell tumors [8]. Those proportions show why lab confirmation matters. You cannot tell the type by feel alone.

Treatment

For most testicular lumps, the treatment is neutering, which removes the affected testicle and often both. This is curative for many cases. When a tumor has already spread, other options exist. In one reported case, a 13-year-old cryptorchid dog with seminoma that had spread to a lymph node was treated with radiation therapy, and the tumor shrank from 343.3 cm3 to 42.4 cm3 within four weeks [9]. Side effects in that case were mild diarrhea and reduced appetite that resolved on their own within two weeks [9]. This shows that even advanced cases can sometimes be managed, though outcomes vary by dog.

Prevention and Monitoring

Neutering is the single most effective step. It removes the tissue where these tumors form and eliminates the risk of a retained testicle becoming cancerous later [2][1]. If your dog is an older intact male, talk with your vet about whether neutering still makes sense. It usually does, and it also removes the risk of testicular tumors going forward.

If your dog is already neutered, testicular tumors are no longer a concern, but scrotal swelling can still happen. Scrotal hernias occurred in both intact and castrated dogs in one review, so a scrotal bulge after neutering still needs an exam [5].

For intact males you are not planning to breed, check the scrotum monthly. Feel both testicles gently and note any change in size, shape, or firmness. Report anything new to your vet.

If you find lumps elsewhere on your dog, these guides can help you understand the possibilities: Why Is My Dog having lumps on skin? Lipoma vs Mast Cell vs Cyst Diagnosis and Lump Under Dogs Skin: Comprehensive Veterinary Reference Guide.

Limitations and When to Contact a Veterinarian

This article cannot tell you what your dog's lump is. Only a veterinarian who examines your dog, reviews imaging, and sees the tissue report can do that. Individual cases need a veterinarian.

Use this timing guide:

Emergency now: scrotal swelling with vomiting, a hard or painful abdomen, sudden severe enlargement, or inability to urinate.
Same day: a warm, painful, red scrotum, fever, lethargy, or a dog that will not eat.
Within a few days: a new firm lump on a testicle, a change in size of one testicle, or a testicle that cannot be found in the scrotum.
Routine visit: a stable lump you have been monitoring, or a general checkup for an older intact male.

Do not wait months to have a testicular lump evaluated. These tumors are common, and early removal gives the best chance of a simple fix.

Frequently Asked Questions

Can a puppy get a lump on its testicle?

Yes, though it is uncommon. Young dogs can develop orchitis, hernias, or other swelling in the scrotal area, and scrotal hernias have been reported in dogs as young as a few months old [5]. Any new scrotal lump in a puppy should be checked, because a testicle that has not descended normally needs attention early.

Is a dog lump on the genital area male always cancer?

No. Inflammation of the testicle, hernias, and other non-cancerous conditions can all cause swelling in that area [3][5]. That said, testicular tumors are the most common tumor of the male reproductive tract in dogs, so cancer is a real possibility that needs testing [1].

Does neutering cure a testicular tumor?

For tumors confined to the testicle, removing the testicle is curative in most cases. If the tumor has already spread to lymph nodes or elsewhere, surgery alone may not be enough, and other treatments such as radiation may be considered [9]. Your vet will stage the disease before deciding on the full plan.

Can a dog lump in the testicle be felt if the testicle never dropped?

Not from the outside. A retained testicle sits inside the abdomen, so a tumor there cannot be felt in the scrotum. Retained testicles carry a higher risk of tumor development, which is one reason neutering is recommended for cryptorchid dogs [1]. Ultrasound or other imaging is needed to find the tissue.

How do veterinarians tell which type of testicular tumor it is?

They send the removed tissue to a laboratory for microscopic analysis. Ultrasound can detect a tumor and show blood flow patterns, but different tumor types often look alike on basic imaging, so it cannot reliably separate them [4]. The final answer comes from the tissue itself, where types such as seminoma, Sertoli cell tumor, and Leydig cell tumor are identified [1][8].

References

Histological Analysis of Multiple Unilateral Testicular Tumors in Dogs. Life (Basel, Switzerland), 2025.
The Gonads and Genital Tract of Dogs - Dog Owners. Merck Veterinary Manual.
Testicular vascularization in healthy dogs using a microvascular flow imaging technique - MicroV. Brazilian journal of veterinary medicine, 2026.
Characterization of Testicular Tumor Lesions in Dogs by Different Ultrasound Techniques. Animals : an open access journal from MDPI, 2022.
Scrotal hernias in dogs should not be ruled out based on castration status and may require enterectomy. Journal of the American Veterinary Medical Association, 2026.
Detection of spermatogonial stem cells in testicular tissue of dogs with chronic asymptomatic orchitis. Frontiers in veterinary science, 2023.
Transmissible Venereal Tumor in Dogs - Dog Owners. Merck Veterinary Manual.
Vimentin expression in canine testicular tumors: a local invasion predictive biomarker. Biotechnic & histochemistry : official publication of the Biological Stain Commission, 2025.
Radiation therapy in a Yorkshire terrier with seminoma and persistent Müllerian duct syndrome. The Canadian veterinary journal = La revue veterinaire canadienne, 2025.