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Total prostatectomy for treatment of prostatic carcinoma in dogs | VETgirl Veterinary Continuing Education Podcasts

In this VETgirl online veterinary continuing education podcast, we review total prostatectomy for the treatment of prostatic carcinoma in dogs.

If you just diagnosed a dog with prostatic neoplasia, what should you do? Dogs are one of the few species known to spontaneously develop prostatic neoplasia. Prostatic carcinoma is the most common diagnosis of neoplasia, with transitional cell carcinoma (TCC), adenocarcinoma (ADC), and squamous cell carcinoma (SCC) being other differentials. Unfortunately, in male dogs, prostatic carcinomas are often diagnosed late, with high rate of local invasion and distant metastasis at the time of diagnosis. Traditionally, treatment options for prostatic neoplasia include NSAIDs, chemotherapy, radiation therapy, photodynamic therapy, and surgery. Surgical options include total prostatectomy (a surgery with curative intent), partial prostatectomy, transurethral resection, urethral stenting, and urinary diversion (all palliative-intent procedures).

But what’s the overall prognosis for prostatic neoplasia?

Previously reported survival times vary from 17-654 days, depending on stage at time of diagnosis. With total prostatectomy, reported survival times for prostatic neoplasia in dogs was 5-45 days (Vlasin), and was considerably shorter as compared to subtotal intracapsular prostatectomy (Vlasin). Unfortunately, urinary incontinence can occur as a post-operative complication (similar to humans) secondary to total prostatectomy; previous studies of prostatectomy in dogs report a range of this complication from 33-100% (Basinger, Goldsmid).

There are very few reports of prostatectomy, especially focused on patients with prostatic neoplasia. So, Bennett et al wanted to evaluate this in a study called Total prostatectomy as a treatment for prostatic carcinoma in 25 dogs (Bennett). This was a multi-center, VSSO-approved (Vet Society for Surgical Oncology) study that specifically looked at signalment, presenting signs, complications, diagnosis and outcome in dogs treated with total prostatectomy for prostatic neoplasia between 2004-2016. In this study, a total of 25 dogs were evaluated, with a median age of 9.3 years and a median weight of 25.0 kg. All of the dogs were neutered males with the Laborador retriever being the most common (n=5), followed by mixed breeds (n=5) and German Shepherds (n=2). In this study, the signalment and presenting clinical signs were similar to prior reports.

In this study (Bennett), the most common clinical signs seen in these dogs with prostatic neoplasia included dysuria, dyschezia, gross hematuria, pollakiuria, hyporexia and lethargy. Prostatic enlargement was found as an incidental findings in 4 dogs via rectal exam and was present in 16/25 (64%) of dogs overall. Two dogs had a caudal abdominal mass on abdominal palpation. All of the dogs underwent total prostatectomy, and all dogs survived to discharge. Following total prostatectomy, various urethral reconstruction procedures were performed and included urethrourethral anastomosis (n=14), cystourethral anastomosis (n=9), ureterocolonic anastomosis (n=1), and anastomosis between the bladder neck and penile urethra (n= 1). Post-operatively, a urinary catheter was left in-situ in 20 dogs and maintained for a median of 4 days post-op. As for histologic diagnoses, 60% (n=15) of dogs were diagnosed with TCC (15 dogs), 32% (n=8) of dogs with prostatic adenocarcinoma, and 1 dog each with prostatic cystadenocarcinoma and undifferentiated carcinoma. 84% (21/25) of dogs had post-operative adjunctive therapy, including NSAIDs, piroxicam, mitoxantrone, metronomic thalidomide, cyclophosphamide, or carboplatin. There was no significant difference in mean survival times for dogs that received the maximum tolerated dose (MTD) or chemotherapy versus those that did not.

When looking specifically at complications in this study, these were defined as minor versus major. Minor complications were defined as self-limiting or those managed with medical intervention. Major complications were defined as any complication that was expected to cause death without rapid intervention, or that required a second surgical procedure. 60% (n=15) of dogs had minor complications, with 16% (n=4) developed major complications. Post-operative urinary incontinence was present in 8/23 dogs (4/14 dogs with urethrourethral anastomosis, 4/9 with cystourethral anastomosis). This 34.8% rate of post-operative permanent urinary incontinence falls within with prior reports of 33-100%. Owners should be made aware of this high rate of complication.

34.8% permanent urinary incontinence rates is in line with prior studies, but is on the low end of prior reported rates. It is suspected that both the presence of prostatic disease contributes to incontinence. Prior studies compared two groups of dogs that underwent prostatectomy, one group of dogs with prostatic disease and another group with normal prostates pre-operatively. The dogs with prostatic disease had lower external urethral sphincter pressures post-op as compared to the normal dogs post-op, suggesting that the present of prostatic disease itself affects urethral sphincter pressures (Basinger, Basinger). These lower sphincter pressures may contribute to incontinence. Since the neurovascular supply to the bladder neck and prostate is located dorsally, dissection in this area may also contribute.

In 14/24 dogs with available data, the median disease free interval was 81.5 days. Overall, the mean survival time in dogs was 231 days, with a slightly shorter MST for prostatic TCC of 189 days, and a longer MST of 248 days for prostatic adenocarcinoma. The survival times were not statistically significant between diagnoses, however.

Local recurrence occurred in 32% of dogs (8 dogs total: 3 confirmed, 5 suspected). Metastatic disease occurred in 13 dogs (4 confirmed, 9 suspected) to the lung, sublumbar lymph nodes, pelvis, vertebrae,  and adrenal glands. This study found similar metastatic rates (52%) as prior studies (63-89%) (Liptak), but no association was found in this study between lympatic/vascular invasion and metastatic disease.

In 76% of dogs (19/25), death was considered to be due to tumor-related causes. 3 dogs were euthanized for other non-tumor related causes and 3 still alive at time of writing (65-2155 days post-operatively). The 1- and 2- year survival rates in this study was 32% and 12%, respectively. The mean survival time was shorter when the prostatic tumor was extracapsular (outside the prostatic capsule) versus intracapsular. Also, the presence of extracapsular disease was the only histologic factor to be statistically associated with outcome.  As for specific type of neoplasia, there was no difference in survival times between prostatic TCC and adenocarcinoma.

The pros of this study? This multi-institutional study shows us that total prostatectomy is a viable alternative with good post-op outcome in certain patients. This provides options for patients that were previously given a very poor prognosis and bad surgical outcomes. It is unclear based on this data if post-operative adjuvant therapy extends survival times, but this is still recommended by the authors.

The limitations of this study? This study may have inadvertently selected for patients with lower pre-operative metastatic rates, smaller tumors and lack of extracapsular invasion since it was based on patients that had been deemed good surgical candidates by the operating surgeons. Prolonged survival times should then be interpreted based on the patient population here. Also, due to the small sample size, it may have predisposed the study findings to type II errors. Also, this study did not compare patients getting surgery alone versus surgery plus post- op adjuvant treatment. Finally, this study was not able to make comparisons between presence of extracapsular disease and local recurrence or local recurrence and mean survival time; this information could be helpful in further identifying good surgical candidates and patients that would maximally benefit from curative-intent total prostatectomy. The authors also stated that case selection likely played a significant role in postoperative outcome.

So, what do we take away from this VETgirl podcast?

Total prostatectomy, along with adjunctive therapy, can prolong survival and have lower complication rates when compared to prior reports. Overall, the mean survival time was 231 days post-operatively, which is a marked improvement as compared to previously reported prognosis (some with a mean of 19 days!). Case selection likely plays an important role in positive outcomes post-operatively. When in doubt, help minimize the risks of prostatic neoplasia with early detection – perform a rectal exam on all your male dog patients at each visit! And if you find abnormalities in the prostate, get them worked up and referred ASAP for possible surgery to help improve the outcome in these canine male patients!

References:
1: Vlasin M, Rauser P, Fichtel T, et al. Subtotal intracapsular prostatectomy as a useful treatment for advanced-stage prostatic malignancies. J Vet Intern Med 2006;47:512-516.
2: Basinger RR, Rawlings CA, Barsanti JA, et al. Urodynamic alterations associated with clinical prostatic diseases and prostatic surgery in 23 dogs. J Am Anim Hosp Assoc 1989;25:385-392.
3: Basinger RR, Rawlings CA, Barsanti JA, et al. Urodynamic alterations after prostatectomy in dogs without clinical prostatic disease. Vet Surg 1987;16:405-410.
4: Liptak JM, Brutscher SP, Monnet E, et al. Transurethral resection in the management of urethral and prostatic neoplasia in 6 dogs. Vet Surg 2004;33:505-516.
6: Goldsmid SE, Bellenger CR. Urinary incontinence after prostatectomy in dogs. Vet Surg. 1991;20: 253-256.
7: Bennett TC, Matz BM, Henderson RA, et al. Total prostatectomy as a treatment for prostatic carcinoma in 25 dogs. Vet Surg 2018;47:367–377.

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