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Prostate tumours in the dog

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Category: Schede
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  • Disciplina: Urologia
  • Specie: Cane

Malignant prostate tumours usually affect dogs, and only occasionally cats, the prostate of which has an anatomical conformation that is extremely different from that of the prostate of both humans and dogs. 1-4

 

AETIOLOGY AND PATHOGENESIS

To date, the precise aetiology of prostate tumours in the dog has not been identified, despite the major studies that have been carried out, given that the dog, after man, is the only mammal that spontaneously develops neoplasms of this organ.5-6 In a recent study an aberrant clonal polysomy of chromosome 13 was found in two dogs with prostate cancer, while in man the subjects who develop prostate cancer have trisomy of chromosome 7, 8, or 17.5 Apart from these cytogenetic considerations, which are clearly of limited clinical value, it should be noted that prostate cancer may develop in both castrated and non-castrated dogs and the role of androgens in the pathogenesis of prostate cancer does, therefore, remain controversial.7-10

Various studies have shown that castrated dogs may develop prostate cancer and that both genetic factors and breed predispose to this condition10. In the same study, Brayn et al. observed that genetics and breed also played a role in the development of transitional cell carcinomas of the bladder in castrated dogs, leading to the idea that, in the dog, some urothelial tumours of transitional and ductal cells originate from prostate tumours.10

Prostate tumours are prevalently of epithelial origin, although occasionally tumours of mesenchymal origin have been reported.11 More precisely, prostate epithelial tumours originate from the ductal epithelium, where the cells often lack androgenic receptors, thus confirming the limited role of male sex hormones in the pathogenesis of the disease.9  No predisposing environmental factors have been identified.

 

EPIDEMIOLOGY

The incidence of prostate cancer in the dog is 0.2-0.6% of all tumours, however the figure comes from autopsy studies. The average age of onset is 10 years.7,12

 

SIGNS AND SYMPTOMS

The signs and symptoms are secondary to the growth of the tumour, within a highly complex anatomical region, and to its locoregional metastases (with spread to iliac lymph nodes and mostly to the vertebral bodies of the sixth and seventh lumbar vertebrae).

The most commonly found sign in dogs with prostate cancer is prostatomegaly, with an asymmetric enlargement of the prostatic lobes which become hard, usually non-mobile, and painful. Other signs include the presence of tape-like stools (because of compression of the overlying rectum) or haematuria/pyuria caused by the involvement of the underlying urethra. The expansive growth of the tumour may result in invasion of the lumbar nervous plexus or vertebral canal, with consequent lameness and neurological deficits caused by the involvement of  lower motor neurons. Another occasionally reported clinical sign is a trumpet-like posture of the tail.

Of all signs, pain is certainly the most frequent. It is manifested by restlessness, rectal and urethral tenesmus (dysuria/stranguria), lameness of the hind limbs or severe pain during transrectal digital palpation of the prostate, or more simply during dorsal palpation of the lumbosacral vertebral column or deep palpation of the caudal abdomen.

All the above signs and symptoms are also found in many other diseases; pain is frequently present in subjects with prostate cancer but it is not sufficient to be able to make a definitive diagnosis.

 

DIAGNOSTIC EXAMINATIONS

Transrectal palpation, when possible in an alert patient, can confirm the presence of prostatic enlargement, determine the shape of the organ and presence of pain and give a rough indication of the possible involvement of other organs.

Among the instrumental investigations, direct X-rays of the caudal abdomen may show the  enlarged prostate and any lymphoadenomegaly as well as alterations of the ventral margin of the cortical bone of the bodies of lumbar vertebrae L6 and L7.

Abdominal ultrasound examination allows a better view of the prostate, of the continuity of the prostatic capsule as well as of any involvement of the urethra. Recently the use of ultrasound contrast media was proposed for better visualisation of the vascular compartment; in a study on a limited number of subjects this strategy successfully allowed differentiation between benign and malignant lesions, later confirmed by histology.13,14  Abdominal ultrasonography also enables visualisation of the iliac lymph nodes and, during the same examination, inspection of both the retroperitoneal space and the entire abdomen, with the goal of detecting any possible kidney involvement (hydronephrosis/hydroureters in the case of involvement of the bladder trigone) and identifying any metastatic foci (particularly in the liver and other lymph nodes).

In a recent study, direct radiography of the caudal abdomen was compared to ultrasonography for the identification of prostate mineralization. The study concluded that castrated subjects with prostate mineralization have a higher probability of having prostate cancer, while sexually intact dogs with no prostate mineralization are less likely to develop prostate tumours.15

Computed tomography X-ray (CTX) with a contrast medium and nuclear magnetic resonance imaging are two extremely important diagnostic techniques which can be used to visualise the prostate and establish its contiguity/continuity with the viscera and the skeleton. In addition, CTX enables the entire abdomen and thorax to be inspected in the same session in order to exclude the presence of metastases.

The definitive diagnosis of a prostate tumour is based on cytology and/or histology. The specimen for the cytological/histological studies may be taken under ultrasound guidance, under CTX guidance or by a surgical coeliotomic approach. Although the percutaneous ultrasound-guided and CTX-guided approaches are less invasive and less laborious than coeliotomy, neoplastic needle-tract implantation, with consequent spread of tumour cells into the abdomen, has been reported following fine needle aspiration biopsy.16

 

DIFFERENTIAL DIAGNOSES

In the presence of prostate enlargement the more probable differential diagnoses are: 

  • benign prostatic hyperplasia
  • paraprostatic cysts
  • prostatitis
  • prostatic abscess
  • secondary prostatic neoplasms (rare), for example, lymphoma17,18

 

TREATMENT

The management of prostatic tumours depends entirely on the clinical stage. Surgery is indicated when there is no expansion of the prostatic tumour to the capsule, with or without invasion of the regional lymph nodes. It is worth recalling that prostatic surgery may cause post-operative complications, such as urinary incontinence.19-21 Surgery must always be followed by chemotherapy.

Surgery is a palliative procedure when the tumour has invaded the prostatic capsule or in the presence of vertebral or distant metastases. In such cases patients should be offered a protocol based on radiation therapy, possibly with a nuclear accelerator, and systemic chemotherapy. Intra-operative radiation therapy and photodynamic therapy have also been proposed.

As regards pain control, non-steroidal anti-inflammatory drugs (COX-2 inhibitors) should be used while waiting for inclusion into a surgical or non-surgical therapeutic protocol; these drugs can subsequently be continued in combination with chemotherapeutic and radiotherapeutic agents.

Antibiotic treatment is always advised.

 

PROGNOSIS

The prognosis of patients with prostatic cancer is always very poor because of the marked local invasiveness of this malignancy and the high probability of metastases in the regional lymph nodes, lumbar vertebrae and chest.11

 

PREVENTION

The best possible prevention consists in the early detection of prostate enlargement and diagnostic cytology/histology to exclude the presence of neoplasms, especially when the patient has severe pain.

 

Reference list

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  2. LeRoy BE, Lech ME. Prostatic carcinoma causing urethral obstruction and obstipation in a cat.J  Feline Med Surg. 6(6):397-400, 2004.
  3. 3.   Tursi M, Costa T, Valenza F, Aresu L. Adenocarcinoma of the disseminated prostate in a cat.J       Feline Med Surg.10(6):600-2, 2008.
  4. Zambelli D, Cunto M, Raccagni R, et alSuccessful surgical treatment of a prostatic biphasic
  5. tumour (sarcomatoid carcinoma) in a cat. J Feline Med Surg. 12(2):161-5, 2010.
  6. Reimann-Berg N, Willenbrock S, Murua Escobar H,  et al.Two  new cases of polysomy 13 in    canine prostate cancer.Cytogenet Genome Res. 132(1-2):16-21, 2011.
  7. Argyle DJ. Prostate cancer in dogs and men: a unique opportunity to study the disease.Vet J. 180(2):137-8, 2009.
  8. Obradovich J, Walshaw R, Goullaud E. The influence of  castration on the development of prostatic carcinoma in dog: 43 cases ( 1978-1985). J Vet Intern Med  1:183-187, 1987.
  9. Teske E, Naan EC, van Dijk EM, et al. Canine prostate carcinoma: epidemiological evidence of an increased risk in castrated dogs. Mol Cell Endocrinol. 29;197(1-2):251-5, 2002
  10. Sorenmo KU, Goldschmidt M, Shofer F, et al . Immunohistochemical characterization of canine prostatic carcinoma and correlation with castration status and castration time.Vet Comp Oncol. 1(1):48-56, 2003.
  11. Bryan JN, Keeler MR, Henry CJ, et al . A population study of neutering status as a risk factor for canine prostate cancer. Prostate. Aug 1;67(11):1174-81, 2007.
  12. Bacci B, Vignoli M, Rossi F, et al. Primary prostatic leiomyosarcoma with pulmonary metastases in a dog.J Am Anim Hosp Assoc. 46(2):103-6, 2010.
  13. Bell FW, Klausner JS, Hayden DW et al. Clinical and pathological features of prostatic adenocarcinoma in sexually intact and castrated  dogs: 31 cases ( 1970- 1987).  J Am Vet Med Assoc, 199: 1623-1630,1991.
  14. Vignoli M, Russo M, Catone G, et al. Assessment of vascular perfusion kinetics using contrast-enhanced ultrasound for the diagnosis of prostatic disease in dogs. Reprod Domest Anim 46(2):209-13, 2011.
  15. Russo M, Vignoli M, Catone G, et al . Prostatic perfusion in the dog using contrast-enhanced Doppler ultrasound. Reprod Domest Anim. 44 Suppl 2:334-5, 2009.
  16. Bradbury CA, Westropp JL, Pollard RE. Relationship between prostatomegaly, prostatic mineralization, and cytologic diagnosis. Vet Radiol Ultrasound 50(2):167-71, 2009.
  17. Nyland TG, Wallack ST, Wisner ER. Needle-tract implantation following us-guided fine-needle aspiration biopsy of transitional cell carcinoma of the bladder, urethra, and prostate. Vet Radiol Ultrasound. 43(1):50-3, 2002
  18. Winter MD, Locke JE, Penninck DG. Imagingdiagnosis--urinary obstruction secondary to prostaticlymphoma in a young dog. Vet Radiol Ultrasound. 47(6):597-60, 12, 2006.
  19. Assin R, Baldi A, Citro G, et al. Prostate as sole unusual recurrence site of lymphoma in a dog. In Vivo, 22(6):755-7, 2008.
  20. Basinger RR, Rawlings CA, Barsanti JA, et al . Urodynamic alterations after prostatectomy in dogs without clinical prostatic disease.  Vet Surg. 16(6):405-10, 1987
  21. Smith J. Canine prostatic disease: a review of anatomy, pathology, diagnosis, and treatment. Theriogenology. 70(3):375-83, 2008.
  22. Freitag T, Jerram RM, Walker AM, et al. Surgical management of common canine prostatic conditions.Compend Contin Educ Vet. 29(11):656-8, 2007