Canine Testicular Tumors Study Guide

Overview and Clinical Importance

Testicular tumors are among the most common neoplasms affecting the male reproductive system in dogs. They represent approximately 90% of all cancers originating from the male reproductive tract. These tumors are encountered frequently on the NAVLE due to their clinical significance, association with cryptorchidism, and potential paraneoplastic effects including hyperestrogenism and bone marrow suppression.

The three primary types of testicular tumors in dogs are Sertoli cell tumors (SCT), interstitial (Leydig) cell tumors (ICT), and seminomas. These tumors occur with roughly equal frequency in the general population, though their clinical presentation and behavior differ significantly. Approximately 27% of intact male dogs will develop testicular tumors in their lifetime, with incidence increasing substantially in dogs over 10 years of age.

Classification and Cell Origin

Testicular tumors arise from two primary cellular components: sex cord-stromal elements (Sertoli cells and Leydig/interstitial cells) and germ cells (seminomas). Understanding the embryonic origin of these cells is essential for predicting tumor behavior and clinical manifestations.

Tumor Classification by Cell Origin

Epidemiology and Risk Factors

Incidence and Age Distribution

Testicular tumors are most commonly diagnosed in intact male dogs over 10 years of age (median age 10-11 years). The overall incidence appears lower than expected because most dogs are neutered at a young age. Approximately 50% of dogs over 10 years of age may have multiple tumors of different histologic types within the same testicle.

Breed Predispositions

Cryptorchidism as a Major Risk Factor

Cryptorchidism (undescended testicle) is the single most important risk factor for testicular tumor development. Key statistics include:

• Cryptorchid dogs have 13.6 times higher risk of testicular tumors
• Sertoli cell tumors: greater than 20 times more common in cryptorchid testes
• Seminomas: 16 times more common in cryptorchid testes
• Interstitial cell tumors: NOT associated with cryptorchidism
• Abdominal retention poses higher risk than inguinal retention due to increased temperature

Detailed Tumor Characteristics

Sertoli Cell Tumor (SCT)

Sertoli cell tumors arise from the sustentacular cells that line the seminiferous tubules and support spermatogenesis. These tumors are clinically significant due to their propensity for estrogen production and associated paraneoplastic syndromes.

Key Features

Interstitial (Leydig) Cell Tumor (ICT)

Interstitial cell tumors arise from Leydig cells located in the fibrovascular stroma between seminiferous tubules. These cells normally produce testosterone. ICTs are the most common testicular tumor in dogs with descended (scrotal) testicles and are generally benign.

Key Features

Seminoma

Seminomas arise from spermatogonia (germinal epithelium) within seminiferous tubules. They are germ cell tumors that may occur in scrotal or cryptorchid testicles. While most seminomas are benign, they can occasionally exhibit malignant behavior.

Key Features

Clinical Signs and Presentation

Most dogs with testicular tumors are asymptomatic, and tumors are often discovered incidentally during routine physical examination. Clinical signs, when present, depend on tumor type, location (scrotal vs. cryptorchid), hormone production, and presence of metastatic disease.

Physical Examination Findings

• Asymmetric testicles (one enlarged, one potentially atrophied)
• Palpable testicular mass (nodular or diffuse enlargement)
• Scrotal swelling or generalized enlargement
• Inguinal or abdominal mass in cryptorchid dogs
• Contralateral testicular atrophy (due to estrogen suppression of gonadotropins)

Hyperestrogenism (Feminization Syndrome)

Hyperestrogenism occurs in 25-50% of dogs with Sertoli cell tumors and occasionally with seminomas. It results from excess estrogen production by neoplastic cells. Clinical signs correlate better with decreased testosterone:estradiol ratio than absolute estrogen levels.

Clinical Signs of Hyperestrogenism

Diagnostic Approach

Physical Examination

Thorough palpation of both testicles is essential. Look for asymmetry, masses, changes in consistency, and signs of feminization. In cryptorchid dogs, palpate the inguinal region and perform rectal examination to assess sublumbar lymph nodes and prostate.

Laboratory Evaluation

Diagnostic Imaging

Ultrasonography

Testicular ultrasound is sensitive for detecting testicular tumors but cannot reliably differentiate tumor types. Key findings:

Radiography

Thoracic radiographs (3 views) are recommended for staging to evaluate for pulmonary metastases. Abdominal radiographs may reveal masses in cryptorchid dogs or enlarged sublumbar lymph nodes.

Histopathology

Definitive diagnosis requires histopathological examination of the removed testicle. Fine needle aspiration is generally not recommended pre-operatively as it may compromise the testicular-blood barrier, cause spermatic granuloma formation, and obscure disease progression. Histopathology confirms tumor type, assesses margins, and evaluates for vascular or lymphatic invasion.

Treatment

Surgical Management

Castration (orchiectomy) is the treatment of choice for all testicular tumors. Key surgical considerations:

• Remove BOTH testicles (bilateral castration) as cancer may be present in both, even if only one appears affected
• Scrotal ablation may be necessary for large tumors to prevent post-operative seroma formation
• Cryptorchid testicles require abdominal or inguinal surgery depending on location
• Evaluate and potentially excise enlarged regional lymph nodes
• Submit all tissue for histopathology

Management of Bone Marrow Suppression

For dogs with myelosuppression secondary to hyperestrogenism:

• Blood transfusion (packed RBCs, whole blood, or platelet-rich plasma) if severe anemia or thrombocytopenia
• Broad-spectrum antibiotics for secondary infections
• Bone marrow stimulants (limited evidence of efficacy)
• Recovery typically occurs 2-3 weeks after tumor removal if bone marrow is not severely aplastic

Adjuvant Therapy for Metastatic Disease

Prognosis

Overall, prognosis for testicular tumors is EXCELLENT with castration, as most tumors are benign and metastasis is uncommon. Cure rates exceed 85-90% with surgical removal alone.