+ General Considerations

  • Prostatic tumors are very rare in cats and rare in dogs
  • Majority of prostatic tumors (98%) are carcinomas: TCC, ADC, SCC, and undifferentiated carcinoma
  • Intratumoral heterogeneity is common with many prostatic tumors exhibiting ≥ 2 patterns of differentiation (i.e., glandular, urothelial, squamoid, or sarcomatoid) and 50% showing mixed glandular and urothelial pattern
  • Intratumoral heterogeneity is characteristic of lethal malignancy
  • Prostatic ADC: body weight is significantly greater than other tumor types (22.5 kg v 15.0 kg) with significantly greater exposure to male hormones (8 years v 6 years) with 60% intact at diagnosis and median time intact 100%
  • Mesenchymal tumors (i.e., OSA, HSA, FSA, and leiomyosarcoma) account for 2% of prostatic tumors
  • Benign prostatic tumors are rare in dogs
  • Bladder and urethral TCC can extend into prostate

+ Biologic Behavior

  • Prostatic carcinoma is a multistep process as high-grade prostatic intraepithelial neoplasia is considered the precursor to human prostate cancer and strongly associated with invasive carcinoma in dogs and humans
  • Prostatic carcinoma is not associated with benign prostatic hyperplasia
  • Insidious onset and most are advanced with 70%-80% metastatic at diagnosis
  • Diffuse or focal with metastasis common through vertebral sinuses and lymphatics
  • Metastatic sites: sublumbar lymph nodes and lungs most common followed by axial skeleton, liver, colon, kidney, heart, adrenal gland, brain, and spleen
  • Pulmonary metastasis is more common in castrated dogs
  • Bone metastasis is reported in 22%-24% dogs
  • Skeletal metastasis more common in young dogs
  • Axial skeleton is more commonly affected (with an axial-to-appendicular ratio of 3.2:1)
  • Pelvis and lumbar spine account for 45% of skeletal metastases
  • Metastatic lesions in bone have variable radiographic pattern with 75% either productive or mixed
  • Urokinase plasminogen activator has been implicated in the pathogenesis of osteoblastic metastasis
  • Urinary excretion of calcium is used in humans to monitor prostatic bone metastases
  • Metastasis is not affected by duration of exposure to testicular hormones
  • Castration may result in progression of prostatic tumors toward a more aggressive, androgen-independent state, and increase metastatic capacity compared to male intact dogs
  • Direct extension into adjacent organs (i.e., bladder, urethra, colon, and musculature) has also been reported


+ Signalment

  • Medium to large breed dogs are more commonly affected (median body weight 20.5 kg)
  • Mean age 10 years
  • Male intact or castrated dogs with 63% castrated and 37% intact
  • Median age at castration 5 years with < 8% castrated before 6 months
  • Median time from castration to diagnosis of prostatic carcinoma: 7 years

+ Clinical Signs

  • Urinary tract signs in 62% of dogs with prostatic carcinoma, including polyuria-polydipsia, stranguria (30%), hematuria (25%), and obstruction
  • Systemic signs include weight loss, inappetance, and fever (42%-70%)
  • GI signs: tenesmus (30%-45%)
  • Gait abnormality manifesting primarily as pelvic limb weakness and lumbar pain or myelopathy due to spinal metastasis or direct tumor extension (36%-50%)
  • Benign prostatic hyperplasia may occur concurrently and exacerbate clinical signs
  • Lower urinary tract signs are most common in cats with no skeletal metastasis, but soft tissue metastasis is common

+ Diagnosis

  • Diagnosis: thoracic and abdominal radiographs, abdominal ultrasound, prostate cytology, and prostate biopsy
  • Rectal palpation: firm, painful, irregular, nodular, and immobile prostate ± sublumbar lymph node enlargement
  • Survey radiographs: mineralization of prostate suggestive of carcinoma
  • Retrograde urethrography can be used to assess irregular prostatic urethral lining
  • Abdominal ultrasonography: hyperechoic foci ± guided-aspirate or biopsy
  • Cytology of prostatic aspiration or fluid collection may reveal cancer cells
  • Aspirates can be collected via trans-abdominal, perineal, or peri-rectal approaches
  • Acute prostatitis and prostatic abscess are contraindications for prostatic aspirate or biopsy
  • Total acid phosphatase, prostatic acid phosphatase, and non-prostatic acid phosphatase are significantly higher in dogs with prostatic carcinoma compared to normal dogs or dogs with benign prostatic hyperplasia
  • Definitive diagnosis requires tissue biopsy
  • Diagnosis of prostatic carcinoma should not be excluded if other prostatic diseases are diagnosed as prostatic carcinoma has been reported to occur concurrently with benign prostatic hyperplasia, abscesses, and cysts


+ General Considerations

  • Chemotherapy, radiation therapy, and surgery have been attempted but are seldom effective
  • Prostate tumors are unresponsive to androgenic stimulation hence castration is ineffective in the prevention and treatment of prostatic carcinomas
  • However, concurrent benign prostatic hyperplasia will respond to castration and may improve clinical signs

+ Chemotherapy

  • Prostatic neoplasia traditionally does not respond to chemotherapeutic agents
  • Dogs with prostatic carcinoma treated with piroxicam or carprofen have a significantly improved survival time than untreated dogs (6.9 months v 0.7 months)

+ Radiation Therapy

  • Intraoperative and postoperative radiation therapy in dogs
  • Brachytherapy and external beam therapy, either alone or in combination, is used in humans

Surgical Management

+ Tube Cystotomy

  • Palliative procedures are preferred as aggressive approaches (i.e., total prostatectomy) are limited by metastatic disease and complicated by tumor extension into the bladder and urethra and frequent surgical complications
  • Types: tube cystotomy or indwelling urethral catheter

+ Photodynamic Therapy

  • Photodynamic therapy using photosensitizer motexafin lutetium is effective in inducing prostatic necrosis with persistent glandular atrophy with connective and stromal regeneration at 2 mg/kg, but 6 mg/kg results in fatal prostatic necrosis
  • Photodynamic therapy using 5-aminolevulinic acid as a photosensitizer has been used in 1 dog with prostatic carcinoma with a 35 week survival time

+ Transurethral Resection

  • Transurethral resection is a palliative procedure for dogs with urinary obstruction
  • Transurethral resection can be combined with intraoperative radiation therapy and chemotherapy
  • Advantages: no tube drainage

+ Urethral Stening

  • Urethral stenting is a palliative procedure for dogs with urethral obstruction
  • Urethral stenting can be performed either retrograde or normograde
  • 25% urinary incontinence

+ Partial and Total Prostatectomy

  • Total prostatectomy may be a viable option for localized and well-circumscribed prostatic tumors, but the risk of postoperative urinary incontinence is high
  • Partial prostatectomy has been described to decrease the volume of tumor compressing the colon and/or urethra, while preserving the dorsal neural supply to the bladder and bladder neck and hence continence

+ Prognosis

  • Prognosis is poor as prostate tumors are biologically aggressive and usually unresponsive to treatment
  • Overall MST 0 days because > 50% dogs are euthanased at diagnosis
  • MST 30 days for dogs surviving > 7 days after diagnosis