Prostatic tumors are rare in dogs. The majority of canine prostatic tumors are malignant carcinomas, accounting for 98% of prostatic tumors, and include transitional cell carcinoma (TCC), adenocarcinoma, squamous cell carcinoma, and undifferentiated carcinoma. Prostatic tumors have an insidious onset and most are advanced at the time of diagnosis with 70%-80% of dogs having evidence of metastasis. The management of non-metastatic prostatic tumors is challenging because the majority of these dogs present as a result of secondary urethral obstruction or urinary tract infection.
Management options include non-steroidal anti-inflammatory drugs alone or in combination with chemotherapy, tube cystostomy to bypass the urinary obstruction, transurethral resection or ultrasound-guided endoscopic diode laser ablation of the intraurethral component of the prostatic tumor, urethral stents for dogs with secondary urinary obstruction, partial prostatectomy, and radiation therapy. Other than radiation therapy, particularly intensity-modulated and image-guided radiation therapy (IMRT) (see Nolan et al, J Vet Intern Med 26:987-995, 2012), all of these techniques are palliative. Theoretically, for dogs with non-metastatic prostatic carcinomas, control of the local tumor followed by chemotherapy should provide the best chance for resolution of the clinical signs associated with the local prostatic tumor as well as long-term tumor control.
Total prostatectomy has traditionally not recommended for the management of dogs with prostatic tumors because of the high risk of morbidity and no improvement in local tumor control or survival times compared to less aggressive techniques. However, much of this research was performed over 30 years ago when surgery was performed on more advanced cases and when owner tolerance of outcomes such as urinary incontinence was less than it is now. In addition, the inevitability of urinary incontinence following total prostatectomy has been questioned following the publication and personal experience of outcomes following inadvertent total prostatectomy in cryptorchid dogs where urinary incontinence is exceedingly rare. As a result, some surgical oncologists are re-exploring total prostatectomy as an option for the management of dogs with localized, non-metastatic prostatic carcinomas, particularly where IMRT is either not available or declined by the owners.
Dr. Ralph Henderson has extensive experience with total prostatectomy in dogs. Based on his advice, I have been offering total prostatectomy for dogs with non-metastatic prostatic carcinomas confined to the prostate with no extension into the pre- or post-prostatic urethra. Contrast-enhanced CT scans are recommended preoperatively to determine the extent of the local prostatic tumor, as well as for abdominal and thoracic staging. Total prostatectomy is performed through a ventral midline celiotomy. In most cases, a pubic symphyseal osteotomy (Figure 1) or pubic flap is required to access the prostate and post-prostatic urethra for resection and anastomosis. The prostate is dissected free from adjacent tissue with care, especially dorsally where the capsule is closely associated with neurovascular structures important for maintaining continence. The prostate is resected with 1cm margins cranially and caudally (Figure 2) and the pre- and post-prostatic urethra is anastomosed with either a simple interrupted or simple continuous suture pattern (Figure 3). Urinary incontinence is less likely postoperatively with a delicate dissection technique and by preserving the urethral sphincter and urinary bladder neck.
I have now done five total prostatectomies, four for prostatic TCCs and one for a dog with congenital vascular ectasia of the prostate. Three of these dogs required a pubic osteotomy procedure for total prostatectomy whereas total prostatectomy was able to be performed via a caudal ventral midline celiotomy alone in two dogs. One dog had urinary leakage from the anastomosis site and required revision. One dog had a histologically incomplete excision but did not develop local recurrence. One dog was incontinent prior to surgery and continued to be incontinent following surgery. The remaining four dogs were either continent immediately (n=2) or were initially incontinent but regained continence over a 1-3 month period (n=2). The dog with prostatic vascular ectasia is alive, disease-free, and continent 9 years postoperatively. For the four dogs with TCC, three were treated with chemotherapy (mitoxantrone and a non-steroidal anti-inflammatory drug) and chemotherapy was declined for one dog. The one dog treated with surgery alone was euthanatized at 9 months because of suspected local tumor recurrence. Of the three dogs treated with total prostatectomy and chemotherapy, one was lost to follow-up at 12 months (and was disease-free at the time), and two were euthanatized because of lung metastasis 10 months and 13 months postoperatively.
The advantages of total prostatectomy include better local tumor control than any other technique (and hence the resolution of clinical signs commonly associated with non-metastatic prostatic tumors), less expensive than either palliative urethral stenting or curative-intent IMRT, more readily available than IMRT, and a relatively low risk of postoperative complications. The incidence of urinary incontinence following total prostatectomy is similar to urethral stenting (20%-25%). Furthermore, there is the theoretical advantage that chemotherapy should be more effective following adequate local tumor control, but larger case studies are required to investigate whether there is a survival benefit over less aggressive management strategies such as chemotherapy alone. While total prostatectomy is not for every owner, and it should only be offered as a treatment alternative for dogs with localized and non-metastatic prostatic tumors, it does present another option for a select subset of dogs with prostatic carcinomas.
ACVS Founding Fellow in Surgical Oncology
Alta Vista Animal Hospital, Ottawa, Ontario, Canada