This tumour type is located in the prostate. The prostate is a gland that surrounds the urethra at the junction of the bladder neck with the urethra.

Behaviour

Benign prostate tumours are rare. Both castrated and non-castrated male dogs can develop prostate cancer.

Most prostate tumours are characterized by local ingrowth and a high chance of local and distant metastases. Metastases are mainly present in the lungs and lymph nodes, but can also occur in the bones (especially the vertebrae at the level of the lower back and hip).

Prevalence

Relatively uncommon (less than 1% of tumours) with a diagnosis made at the median age of 10 years.

Breed predisposition

A higher risk to develop this tumour type was reported for Airedale terrier, Beagle, Bouvier de Flandres, Doberman Pinscher, German Shorthaired Pointer, Norwegian Elkhound, Scottish Terrier and Shetland sheepdog as opposed to other dog breeds.

Symptoms

Clinical signs vary depending on the tumour size and metastasis’ location. Since the prostate surrounds the urethra, the prostate tumour growth may cause increased pressure on the urethra and/or on the upper intestine. With local growth of the tumour one can notice the following signs: blood in the urine, difficulties with urination/defecation and/or flattened stool. If the urethra is completely compressed, this can increase pressure on the kidneys and lead to kidney issues. Furthermore, the tumour may press against the vertebral bodies or nerves causing discomfort that may manifest through a strange walk, limping and/or constipation.

When the tumour is in an advanced stage, it can lead to general signs of disease such as loss of appetite, apathy, panting, difficulties with breathing, loss of appetite and weight loss. Bone fractures can occur due to metastases in the bone.

Rectal examination

A rectal examination allows the veterinarian to feel whether the prostate has a normal shape. Prostate tumours can cause an irregular shape of the prostate. Abnormally enlarged lymph nodes can be noticed through rectal examination or possibly through palpation of the abdominal cavity.

Blood analysis

Blood tests can indicate anaemia, an excess of white blood cells, calcium and signs of bone damage.

Urine analysis

Through urine analysis, the veterinarian can detect abnormal cells as well as indications for infection.

A positive BRAF mutation testing confirms the presence of transitional cell or prostate carcinoma. If no BRAF mutation is detected in the sample, it may be because (1) there is no cancer present, (2) there is a tumour, but it is not caused by the BRAF gene mutation, (3) the urine sample does not contain mutated cells, even though a carcinoma is present.

Imaging

Through X -rays of the lungs taken from different angles, it is possible to detect the following (if sufficiently large): lung metastases, enlargement of the lymph nodes at the level of the sternum or in rare cases metastases to the ribs or the shoulder bone. Radiographic images of the abdominal cavity can reveal an enlarged prostate, enlarged lymph nodes, and/or anomalies in surrounding bones. Contrast matter in the urethra can also be applied to assess irregularities in the prostate (however, this technique can not differentiate between an inflammation or tumoural process).

If there is uncertainty about metastases to the bone, bone scintigraphy can be used to more accurately determine the location of possible metastases.

Ultrasound of the abdominal cavity can be useful to further assess the prostate, as well as the urethra, bladder, local lymph nodes and other organs in the abdominal cavity.

Cytology

Taking tissue samples is the gold standard for the diagnosis of prostate tumours, but a definitive diagnosis can also be obtained through the aspiration of cells and their subsequent examination (cytology).

A cytologic sample can be obtained in several ways, including ejaculation, insertion of a catheter that scrapes cells away, massage of the prostate, ultrasound-guided aspiration of cells through a needle, imprints obtained during surgery. When sampling through the skin, there is a risk that this will cause bleeding, but also cause the tumour to spread via the needle’s path. In prostate tumours, it is not required to obtain a tissue sample to determine the tumour’s grade as the impact of the grade on the prognosis is unclear.

The tumour can grow unnoticed and has a high tendency to metastasize. Hence, prostate tumours in most dogs are only detected when the disease is already advanced and overall prognosis is poor. Treatment is administered palliatively. No standard treatment is available for prostate tumours, although at least the use of anti-inflammatory drugs is recommended (a high percentage of prostate tumours are responsive to (COX-2-inhibitory) anti-inflammatory drugs).

Surgery

Palliative surgery can be offered (removal of the tumour or maintaining urinary passage via a stent). Removal of the prostate is only recommended when the tumour is still completely encapsulated and has not yet broken through the capsule of the prostate. However, removal of the prostate is also associated with a high degree of post-operative discomfort and it has not yet been clearly demonstrated that it leads to an extension of life. Incontinence is a possible result of prostate removal. Partial removal of the prostate is an alternative with fewer complications and equally good survival results. Complete prostate removal and electrosurgery through the urethra are associated with a high risk of complications.

Photodynamic therapy

Photodynamic treatment remains experimental.

Radiotherapy

Radiation therapy can be helpful in reducing pain associated with bone metastasis, although the optimal dose and fractionation are unknown. Currently, it is unclear if improving local control with radiotherapy will alter the time to or pattern of metastasis.

Chemotherapy

The role of chemotherapy is unclear.

The survival time without treatment is often less than 30 days and most dogs are euthanized at the time of diagnosis.

A study examined the survival times of 25 dogs whom underwent total surgical removal of the prostate. Most of them received adjunctive therapy (such as chemotherapy and/or anti-inflammatory drugs). The median survival time for all dogs was 231 days and dogs with intracapsular tumours had a significantly longer median survival time than those with extracapsular tumours (248 vs 138 days).

In a study with ten dogs with prostatic carcinomas undergoing radiotherapy, the overall survival time was 654 days. Although multimodality therapy and anti-inflammatory drugs were not standardized, results support further prospective evaluation of radiotherapy for long-term control. Given the potential for durable tumour control after radiotherapy, it will be important to monitor for late radiation toxicity, as approximately 20% of dogs developed manageable grade 3 late toxicity (including urethral, ureteral, and rectal stricture).