Testicular tumours are easily prevented through routine castration of male dogs. Castration in young dogs prevents aggression, roaming, urine marking, and a variety of other unwanted male behaviours. The surgery is safe and relatively inexpensive, and in the long run saves the owner money. Dogs that are used for breeding can be castrated when they are no longer used for breeding. Dogs that are cryptorchid should always be castrated and the owner should insist that both testicles be removed. Since cryptorchidism is considered to be an inherited trait, cryptorchid dogs should never be used for breeding. Because the retained testicle is 13 times more likely to develop a tumour, it should always be removed.

Testicular tumours are considered one of the most common tumours in older intact male dogs. Some of these tumours are found within the abdominal cavity if the testicle did not descend into the scrotum. Some of these tumours may produce excessive estrogens which causes hair loss, nipple enlargement and a stripe of inflammation on the prepuce. The prognosis tends to be favourable, as only 10% of these spread. 

What are testicular tumors? 

  • Testicular tumors are considered one of the most common tumors in older intact male dogs.  The overall incidence in dogs is not very high because most dogs dogs are castrated (neutered) at a young age. The three most common types of testicular tumors are Sertoli cell tumors, interstitial (Leydig) cell tumors, and seminomas.  About one third of dogs that develop a tumor will have more that one of these types of tumors present.  Other types of testicular tumors (i.e. embryonal carcinoma, lipoma, fibroma, hemangioma, chondroma, teratoma) can occur, but are rare. 
  • The current cause of testicular tumor development is unknown.  Although they are most common in intact older male dog (>10 years), they can occur in intact males of any age and breed.  Male dogs that have one or both testicles that have not descended from the belly cavity are much more likely to develop a tumor than dogs with normal (scrotal) testicles.       
  • Tumors of normal descended, or scrotal, testicles are usually benign while those still located in the abdomen are much more likely to be malignant.  Testicles retained in the abdomen are predisposed to the development of Sertoli cell tumors and seminomas. The tumor is slow to metastasize and the common site of spreading include lymph nodes.  
  • Tumor specifics
    • Testicular tumors produce excessive hormones such as estrogen or testosterone. 
    • Sertoli cell tumors have a higher rate of spread than other testicular tumors and are more common in cryptorchid testes.  Dogs affected with these tumors show swelling of the testicular or scrotal area. 
    • Interstitial (Leydig) cell tumors are benign and small.  Dogs affected with these tumors show very few symptoms and the tumors are usually incidental findings. 
    • Seminomas arise from the cells of the testicle that normally produce sperm.  The majority of seminomas are benign and they rarely spread.  Seminomas may lead to signs of femal characteristics in a male dog.  Most dogs are not ill, and many of these tumors are found during a routine physical examination.

Clinical Signs

  • Soft swellings in one or both testicles
  • Single enlarged testicle or asymmetric testicles
  • Generalized scrotal enlargement
  • Infertility in the breeding stud
  • Hair & Skin changes:
    • Symmetrical hair loss
    • Brittle hair
    • Poor hair regrowth
    • Thin skin
    • Hyperpigmentation (darkening of the skin)
    • Stripe of red inflammation along the midline of the prepuce
  • Other signs:
    • Nipple elongation (see photo below right) Mammary enlargement
    • Penile atrophy
    • Preputial swelling and sagging
    • Testicular atrophy of the unaffected (non-cancerous testicle)
    • Prostatic atrophy or enlargement
    • Anemia
    • Behavioral changes:
      • Nipple
      • Squatting to urinate
      • Reduced sex drive
      • Attraction of other male dogs


  • History
  • Presentation - see above clinical signs
  • A thorough physical examination including palpation of the testicles; the stripe of inflammation seen along the prepuce (arrow in the photo to the right) is classic for an estrogen producing tumor
  • Complete blood count (CBC)
  • Biochemistry profile
  • Urinalysis +/- culture and sensitivity
  • Chest and abdominal radiographs (x-rays)
  • Abdominal and scrotal ultrasound
  • Fine needle aspiration or biopsy
  • Biopsy of the removed testicle


  • Surgery: Surgical castration or an abdominal exploratory may be performed.
  • Chemotherapy and radiation therapy can be pursued if the tumor has metastasized.  Treatment of metastatic disease should be pursued. 

Potential Complications

  • Anemia - High levels of estrogen can reduce the function of the bone marrow which may lead to significant decreases in the number of white blood cells, red blood cells, and platelets.  The patient is then at risk of developing infections, anemia, and bleeding tendencies that can be life-threatening.
  • Occasionally testicular tumors may predispose the testicle to twist, called testicular torsion.  The twisting of the testicle will cause sudden swelling of the scrotum and pain. 
  • If the tumor has spread and is an estrogen producing tumor; these clinical signs do not disappear even though the cancerous testicle was removed.
  • Complications following properly performed castrations are rare.  Potential complications may include incisional problems such as swelling, infection, bleeding into the scrotum and self-mutilation of the incision.

Aftercare (Home Care)

  • Animals undergoing surgery are monitored for pain, hemorrhage, and infection.  At home the incision and scrotum will need to be checked twice daily for any signs of swelling, redness, or discharge.  If a significant amount of discharge from the incision is present or swelling, infection may be present and antibiotic therapy will need to be prescribed. 
  • A recheck in 10-14 days following surgery is recommended to evaluate incision healing. 
  • If bone marrow disease is present follow-up blood work will need to be performed to monitor for improvement in red blood cell, white blood cell, and platelet numbers. 
  • Patients with malignant tumors should be re-evaluated every three to four months for recurrence or metastasis.


  • Surgery is curative for most testicular tumors. About 10 to 20% of the cases have spread at the time of diagnosis.
    • Interstitial cell tumors and Sertoli cell tumors without spread or damage to the cells of the bone marrow have an excellent prognosis. 
    • Seminomas without signs of hyperestrogenism also have an excellent prognosis. 
    • Damage to the cells of the bone marrow (caused by the excessive estrogen levels) can be fatal despite therapy, but usually improves two to three weeks after tumor removal. 
    • The prognosis for testicular tumors that have spread is more guarded, but varies greatly depending on the location, type of tumor, and treatment options.  

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