+ General Considerations

• Testicular tumors are common and account for 4%-7% of all tumors in male dogs
• Testicular tumors broadly classified into 2 groups based on histology:
• Group I: germ cell tumors such as seminoma, embryonal carcinoma, and teratoma
• Group II: Sertoli cell tumor, interstitial cell tumor, and mixed testicular tumors
• Mixed testicular tumors may be classified separately
• Mixed germ cell-stromal tumors have a dual population of germ and Sertoli cells and account for 7% of canine testicular tumors
• Breed predisposition: Siberian Husky, Norwegian Elkhound, Fox Terrier, Afghan Hound, and Shetland Sheepdog
• Dachshund, Rottweiler, Shih Tzu, Yorkshire Terrier, Toy Poodle, Miniature Schnauzer, and mixed breed dogs have a significantly decreased risk of developing testicular tumors

From: Withrow SJ & MacEwen EG (eds): Small Animal Clinical Oncology (3rd ed).

• 50% of dogs over 10 years have multiple tumors of different histologic types
• Testicular tumors are uncommon in dogs < 6 years
• Sertoli cell tumor and seminoma are more common with cryptorchid testicles

+ Sertoli Cell Tumor

• Sertoli cells produce estrogen, support germ cells, and form seminiferous tubule basement membrane
• Sertoli cell tumors tend to grow in expansile fashion that compress and destroy surrounding parenchyma
• Sertoli cell tumors are bilateral in 11% dogs
• 54% of Sertoli cell tumors are found in cryptorchid testicles
• 8.8-times risk of developing a Sertoli cell tumor in the cryptorchid testicle compared to descended testicle in dogs with unilateral cryptorchidism
• Testicular microenvironment influences the development of testicular tumors as, in humans, early surgical correction of cryptorchidism (i.e., orchipexy) decreases risk of testicular neoplasia
• Sertoli cell tumor in descended testicle found in younger dogs and associated with contralateral cryptorchid testicle
• Sertoli cell tumors are associated with a decreased risk of prostatic disease, circumanal gland hyperplasia, perianal tumors, and perineal hernia
• 0.6%-9.0% metastatic rate with metastatic sites including sublumbar lymph node (common), lungs, liver, spleen, adrenal glands, kidney, and pancreas

+ General Considerations

• Incidental finding at surgery or necropsy
• Scrotal or inguinal mass or enlargement
• Hypertrophic osteopathy reported in 1 dog with metastatic Sertoli cell tumor to lungs and kidney

+ Feminization Syndrome

• Feminization is rare in dogs with interstitial cell tumors and seminomas, but can occur with Sertoli cell tumors
• Feminization dependent on testicular location with feminization occurring in 16% of scrotal testes, 50% of inguinal testes, and 70% of intra-abdominal testes
• Hyperestrogenism has been implicated in the pathogenesis of feminization but this has not been proven
• Clinical signs of feminization include:
• Bone marrow hypoplasia with thrombocytopenia, hemorrhage, anemia and granulocytopenia
• Symmetrical and squamous metaplasia of the prostate resulting in cystic benign prostatic hyperplasia
• Gynecomastia and galactorrhea
• Attractiveness to other males
• Atrophy of non-neoplastic testicle due to negative feedback of estrogen on the pituitary-hypothalamus axis
• Penile atrophy with pendulous prepuce
• Bilaterally symmetrical alopecia in the genital area, inner thighs, abdomen, chest, shoulders, and thighs
• 69% mortality rate

+ Diagnosis

• Scrotal palpation
• Rectal examination, lateral abdominal radiograph, abdominal ultrasonography, or direct examination during exploratory celiotomy to assess ± biopsy the sublumbar lymph nodes
• Ultrasound examination is a sensitive and relatively specific technique for the diagnosis of testicular tumors with:
• Interstitial cell tumors appearing as a well-circumscribed mass with predominantly hypoechoic and small hyperechoic areas
• Sertoli cell tumors disrupting internal architecture with echogenic pattern varying from anechoic to mixed echogenicity
• Aspiration or biopsy are invasive, compromise testicular-blood barrier and may predispose to infertility and spermatic granuloma formation
• ± thoracic radiographs
• Histopathology following castration

+ Treatment

• Castration with resection of a large amount of the spermatic cord
• Fresh whole blood transfusion for dogs with Sertoli cell tumors if myelosuppressed with thrombocytopenia and anemia

+ Prognosis

• Castration is curative if no bone marrow hypoplasia, myelosuppression, or metastatic disease
• Mortality > 80% if severe myelosuppression
• Hematologic parameters usually improve within 2-4 weeks but can take up to 5 months to return to normal