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
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
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
