Veterinary Society of
Surgical Oncology

Types

  • 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 Behaviour

  • 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

CLINICAL FEATURES

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

TREATMENT

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

PROSTATIC TUMORS

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