PATHOPHYSIOLOGY

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

Seminoma

•seminomas arise from germinal epithelium and are usually solitary masses

•seminomas are bilateral in 18% dogs

•34% of seminomas are found in cryptorchid testicles

•16-times risk of developing seminoma in the cryptorchid testicle compared to descended testicle in dogs with unilateral cryptorchidism

•seminoma in descended testicle found in younger dogs and associated with contralateral cryptorchid testicle

•seminomas are associated with prostatic disease and enlargement, circumanal gland hyperplasia, and perianal tumors ± perineal hernia

•< 10% metastatic rate

•metastatic sites including sublumbar lymph node (common), lungs, liver, spleen, adrenal glands, pancreas, CNS, eyes, and skin

•AgNOR counts are higher in dogs with metastatic seminoma compared to non-metastatic seminoma

Other Testicular Tumors

•other tumors include hemangioma, granulosa cell tumor, sarcoma, embryonal carcinoma, gonadoblastoma, and LSA

•testicular teratoma is very rare in dogs

•metastatic testicular tumors from GI ADC have been reported in 3 dogs

CLINICAL FEATURES

Clinical Signs

•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 is rare in dogs with seminomas

Diagnosis

•scrotal palpation

•rectal examination, lateral abdominal radiograph, abdominal ultrasonography, or direct examination during exploratory celiotomy to assess ± biopsy the sublumbar lymph nodes

•infertility associated with spermatozoal abnormalities such as lesions in mid-piece region, poor spermatozoal motility, and low total spermatozoal output

•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

•137cesium external beam radiation therapy has been used in 4 dogs with metastatic seminoma with CR in 3 dogs and no evidence of recurrence

•platinum-based chemotherapy protocols are recommended in humans and dogs with metastatic seminoma

•bleomycin used successfully in 1 dog with cutaneous metastasis with no recurrence by 12 months

•vincristine and cyclophosphamide were not effective in 1 dog with cutaneous metastasis

Prognosis

•castration is curative if no bone marrow hypoplasia, myelosuppression, or metastatic disease