Cancer of the Testicles in Dogs

Key Points

Testicular cancer is very common in intact male dogs

Most tumors are contained to the testicles, but may spread in 10 to 20% of the cases

Surgery is the the treatment of choice

Prognosis is usually very good



  • In one study showed that 27% of male dogs develop testicular tumors.1
  • Sertoli cell tumors, interstitial (Leydig) cell tumors, and seminomas are the three most common tumors.  Seminomas (42%) and interstitial cell tumors (50%) are most common with sertoli cell tumors being the least common (8%). 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.   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.
  • Undescended testicles (located in the abdomen or groin) are at increased risk to develop malignant behaving tumors (seminomas and Sertoli cell tumors). Tumors of normal descended, or scrotal, testicles are usually benign.  The tumor is slow to metastasize and the common site of spreading include lymph nodes.
  • Testicular tumors can spread to regional lymph nodes, liver and lungs.
  • Specific tumors characteristics
    • Sertoli cell tumors
      • higher rate of spread than other testicular tumors
      • more common in undescended testes.
    • Interstitial (Leydig) cell tumors
      • are benign and small
      • show very few symptoms
      • these tumors are usually incidental findings
    • Seminomas
      • arise from the cells of the testicle that normally produce sperm
      • majority are benign and they rarely spread.
      • may produce estrogen and result in feminization

testicular tumor Clinical Signs

  • Any breed can be affected and are found in older dogs (greater than 10 years) and obviously in intact males
  • Swelling of one or both testicles
  • Generalized scrotal enlargement
  • Infertility in the breeding stud
  • Effects of excessive estrogen levels due to tumor:
    • 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 (large arrow in photo right)
    • Nipple elongation (small arrow in photo right)
    • Mammary enlargement
    • Penile atrophy
    • Preputial swelling and sagging
    • Testicular atrophy of the unaffected (noncancerous testicle)
    • Prostatic atrophy or enlargement
    • Anemia
    • Behavioral changes:
      • Nipple
      • Squatting to urinate
      • Reduced sex drive
      • Attraction of other male dogs


  • A thorough physical examination including palpation of the testicles for a mass; the stripe of inflammation seen along the prepuce (arrow in the photo above) is classic for an estrogen producing tumor
  • Complete blood count (CBC) – to check for anemia
  • Biochemistry profile – to check internal organ health prior to surgery
  • Urinalysis +/- culture and sensitivity – to check for concurrent bladder infection
  • Chest and abdominal radiographs (x-rays) – to check for spread of tumor
  • Abdominal and scrotal ultrasound – to check for tumor and spread of tumor
  • Fine needle aspiration or biopsy – not commonly performed, but may be helpful to arrive at a diagnosis prior to surgery
  • Biopsy of the testicle after it is surgically removed


  • Surgical removal of the testicles is performed. This surgery is typcially very routine, however the scrotal skin should also be removed to prevent the development of a large painful swelling of the scrotum after surgery.
  • Chemotherapy can be pursued if the tumor has metastasized.  Treatment of metastatic disease should be pursued.
  • Radiotherapy

Potential Complications

  • The most common complication is marked swelling of the scrotum if it is not ablated at the time of castration.
  • Infection is uncommon
  • High estrogen levels may result in bleeding and anemia due to bone marrow suppression
  • Spread of the tumor will ultimately cause death of the patient

Care after surgery

  • Check the incision daily for 14 days for signs of infection: swelling, redness, pain or discharge.
  • 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 reevaluated 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.


  1. Grieco V, Riccardi E, Greppi GF, et al. Canine testicular tumours a study on 232 dogs. J. Comp Path 138: 86-89, 2008.
  2. McDonald RK, Walker M, Legendre AM, et al. Radiotherapy of metastatic seminoma in the dog. J Vet internal Med 2:103-107, 1988.
  3. Dhaliwal RS, Kitchel BE, Knight BL, et al. Treatment of aggressive testicular tumors in four dogs. J Am Anim Hosp Assoc 35: 311-318; 1999.

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