Interstitial Cell Tumor in Dogs


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An interstitial cell tumor is a benign tumor of the testicle. There are no specific causes identified and it is more common in dogs than cats.

This tumor is more common in older dogs and is seen in all breeds, although boxers may be predisposed. Many individuals do not show any clinical signs. The owner may notice enlargement of one or both testicles, change in shape, or change in texture.

Occasionally, these tumors are associated with estrogen secretion, causing feminization (female-like characteristics) and bone marrow suppression.

What to Watch For

  • Gynecomastia (enlarged breasts)
  • A pendulous prepuce (sheath that covers the penis)
  • Alopecia (hair loss)
  • Hyperpigmentation (dark colored skin)
  • Decreased libido and fertility
  • Bleeding (secondary to decreased platelets)
  • Weakness (due to anemia)
  • Infection


  • Baseline tests, to include a complete blood count (CBC), biochemical profile, and urinalysis are recommended. Although usually within normal limits, occasionally there may be various cytopenias (low cell counts of either red blood cells, white blood cells, and/or platelets).

  • Abdominal radiographs (X-rays) may be recommended in some cases.

  • Ultrasound of the abdomen and testicles may reveal changes in the prostate or lymph nodes, locate an undescended testicle, and/or support testicular changes consistent with a testicular tumor.

  • Cytologic examination of the testicular mass may support a diagnosis of an interstitial cell tumor.

  • Definitive diagnosis is based on excision and biopsy of the testicle/mass.


  • Castration is the treatment of choice and is curative.
  • Supportive care may be necessary in cases with associated estrogen suppression and bone marrow hypoplasia.

    Home Care and Prevention

    Follow the instructions given to you by your veterinarian. Recovery in cases with bone marrow involvement is variable, depending on the cell types involved. Feminization generally resolves within 60 days of neutering. Prognosis is good.

    The best preventative measure is to neuter your pet.

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