Introduction

Prostatic tumors develop following abnormal growth of cells in the prostate or in the urethra that spread to the prostate. Most of these tumors are either transitional cell carcinomas (TCC) or adenocarcinomas. It can be difficult to differentiate between the two, however, the behavior and treatment for both is similar. Prostatic tumors are locally aggressive and carry a high likelihood of metastasis to local lymph nodes, lung and bone.

While surgical removal of the prostate would be an ideal treatment method, it is not the most practical as it is associated with a high complication rate and mortality risk, and has little impact on overall survival. Alternatively, a combination of radiation therapy and IV chemotherapy is usually recommended.

Unfortunately, the prognosis for dogs with prostatic carcinoma is poor. Without treatment, median survival time is often less than 30 days. The goal of treatment is to control the clinical signs associated with the tumor and increase quality of life. Generally, clinical signs can be controlled for 4 to 8 months.

Case History

Memphis, a ten-year-old castrated male mixed breed canine was presented to the Iowa State University (ISU) Emergency service for persistent dysuria, pollakiuria and further evaluation of a mass associated with his prostate. On physical exam, his bladder was enlarged but comfortable, and he did not appear to show signs of pain, although he was unable to urinate.

Approximately one month prior, the owners noticed that Memphis was straining to urinate. After no improvement with antibiotics, an abdominal ultrasound was performed which revealed a prostatic mass. He was prescribed piroxicam to help with the pain and inflammation, however, his clinical signs persisted, prompting his owners to present him to ISU.

Treatment Methods

A repeat abdominal ultrasound was performed and confirmed the presence of a prostatic mass with mineralization and urethral compression. A fine needle aspirate of the mass was taken and cytology was consistent with prostatic carcinoma. There was no evidence of metastasis found on abdominal ultrasound, or abdominal and thoracic radiographs.

Because the prostate is positioned around the urethra, the presence of a prostate mass can cause it to become compressed, rendering a patient unable to urinate. Since Memphis was already straining, it was recommended that he have a urethral stent placed to physically keep his urethra open, preventing his bladder from becoming overly distended. He was placed under general anesthesia for placement of the stent which was measured to span the distance of the compressed portion of the urethra. It is important to note that over time, the mass could continue to grow and cause urethral compression outside of the stented area, causing a secondary urinary obstruction.

Following placement of the stent, Memphis’ owners elected to pursue definitive radiation therapy in conjunction with IV chemotherapy. A CT scan was completed for radiation planning and a radiation therapy plan was developed by a radiation oncologist. Memphis’ plan required him to be placed under general anesthesia every day (Monday-Friday) for a total of 20 treatments. Memphis received intensity-modulated radiation therapy (IMRT), a type of radiation that allows us to specifically target the tumor with little impact on the surrounding normal tissues.

During his first week of radiation therapy, Memphis also received his first dose of IV mitoxantrone chemotherapy. This was given every three weeks for a total of four doses with some treatment delays as needed due to expected toxicities. Typically, 4–6 doses of mitoxantrone are recommended for the treatment of transitional cell carcinoma (TCC), however, there is little evidence to suggest that 6 doses yield a longer survival time than 4, and the number of treatments are up to the discretion of the attending oncologist. Memphis’ owners elected to finish chemotherapy after his fourth dose. Having a urethral stent in place meant that Memphis would continue to leak urine during and after chemotherapy administration. Presence of metabolites can be found in the urine of chemotherapy patients, which meant that Memphis’ family and medical team were at an increased risk of exposure to chemotherapy. Extra precautions were taken to protect the people involved with Memphis’ care both in the clinic and at home while he received treatment.

Results and Outcomes

At the end of his chemotherapy and radiation therapy protocols, Memphis had clinically stable disease: his prostate palpated normally on rectal exam and there was no evidence of pain or discomfort (thoracic radiographs and abdominal ultrasound were declined). Approximately 2 months after completion of chemotherapy, an abdominal CT scan showed severe left medial iliac lymphadenopathy, a mineralized area in the right medial iliac lymph node, and possible metastatic spread to the vertebrae. However, his thoracic radiographs were not indicative of metastatic spread to the lungs and his prostate was decreased in size compared to its size prior to radiation therapy.

As these findings indicated that Memphis was likely out of remission, he received IV carboplatin as a rescue agent. Unfortunately, at his appointment for his second dose of carboplatin, he had a markedly decreased appetite, muscle wasting, weight loss and hind limb edema (probably due to enlarged lymph nodes causing lymphedema). Due to his clinical condition he was considered to have further progressive disease. It was decided to discontinue chemotherapy at that time and pursue palliative care. Zoledronate, an aminobisphosphonate, was used to control Memphis’ bone pain associated with his suspected metastatic spread to the vertebral bodies. This was given IV and in conjunction with oral Gabapentin and Amantadine to help keep Memphis comfortable for as long as possible.

Memphis was humanely euthanized approximately one month later, due to continued disease progression and inability to adequately control his pain. Unfortunately, his disease progressed rapidly. However, due to a combination of many treatment methods, he was able to enjoy a good quality of life and seven extra months with his owner.

Unfortunately, even with multimodal therapy, prostatic carcinomas are difficult to treat and early detection is imperative to control clinical signs and give our patients longer survival times.

References

1.  Vail DM, Thamm D, Liptak J. Withrow and MacEwen’s Small Animal Clinical Oncology - E-Book, 6th ed. St. Louis, MO: Elsevier Health Sciences; 2019.