Page 658 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

636 PART IV Specific Malignancies in the Small Animal Patient

The benefit of systemic therapy to manage canine prostatic development of PCA, preventative measures have focused on
tumors is also unclear, although a study demonstrated a clear sur- low-fat diets, regular exercise, and maintenance of a normal body
Like in dogs, most prostatic tumors in men are
219
mass index.
vival benefit in dogs with PCAs treated with piroxicam or carpro-
VetBooks.ir fen compared with those dogs that were untreated (MSTs of 6.9 carcinomas; however, the incidence of disease is considerably
The role of chemotherapy
200
higher in men. Because the dog is one of the few domestic spe-
months vs 0.7 months, respectively).
is less clear. cies to develop spontaneous PCA, there is indeed considerable
For dogs with skeletal metastasis, palliative options include interest in the dog as a model for PCA in men. 135,137–143 Chal-
systemic analgesics, RT, bisphosphonates, and samarium-153– lenges that exist when considering the dog as a model include
ethylenediamine–tetramethylene–phosphonic acid ( 153 SM- the lack of canine PSA that is similar to human PSA, and the
EDTMP). 249–251 Standardized protocols have not yet been most tumors in dogs are likely androgen independent. 133,219,269
determined, although RT and bisphosphonates are widely avail- PCA in men typically initiates as PIN, which is often seen as
able and relatively easy to administer. 249,251–253 multifocal premalignant lesions that progress to neoplasia; the
role of PIN in the development of canine prostatic diseases in
Feline Prostate Tumors either the intact or castrated dog is unclear. High-grade PCA in
men behaves similarly to the disease in dogs, with significant local
Prostate tumors in the cat are rare and reports in the veterinary invasion and a propensity for skeletal metastasis. Although less
literature are sparse. 254–259 Of the few case reports, most tumors common in man, the dog may serve as a good model for inter-
appear to be adenocarcinomas and affect older castrated cats. ventional strategies for androgen-independent, aggressive PCA.
Definitive risk factors have not been identified because of the Therapy in humans is highly dependent on the stage at presenta-
lack of frequent cases and epidemiologic data. Clinical signs often tion and partially dependent on a summary of risks versus benefit
include lower urinary tract signs and obstipation or constipation, of intervention. 219,270–272 Newer robotic surgery approaches are
tenesmus, and dyschezia. Rectal palpation can reveal the presence currently being evaluated in an attempt to improve periopera-
of a mass, which may be further characterized with abdominal tive and postoperative outcome after prostatectomy, which has
ultrasound. There is no standard-of-care therapy in cats and given traditionally been performed as an open or laparoscopic sur-
the paucity of reports in the literature, it is difficult to state over- gery. 272–274 Advances in RT technology have also led to the safe
all prognosis. Metastasis appears common and sites of spread can delivery of higher doses of radiation to prostate tumors, which
include pancreas, lung, and LNs; most cats died within 3 months has improved disease control while maintaining quality-of-life
of diagnosis. 254–258 Prostatectomy for a low-grade prostatic sarco- measures. 219,264,270,275,276 Although there are many nuances to
matoid carcinoma in one cat provided long-term control with no treatment beyond the scope of this chapter, androgen depriva-
evidence of local or metastatic disease at 2 years. 259 Prostatectomy tion therapy generally forms the basis for therapy for hormone-
followed by doxorubicin and cyclophosphamide was reported to sensitive prostate cancer; for CRPC, improvements in outcome
yield a survival duration of 10 months in another cat. 255 Until may be possible with docetaxel with or without novel targeted
more cats with PCA prostatic carcinoma are evaluated, therapy drugs such as abiraterone, a cytochrome P450 (17) inhibitor,
and prognosis are unclear. and enzalutamide, an antiandrogen. 219,277–279 The approaches to
screening and treatment are changing rapidly and warrant atten-
Comparative Aspects tion as novel drugs are developed, as many of these drugs that
have efficacy against CRPC may be applicable to canine PCA.
The recommendations for diagnosis and treatment of PCA in
men have changed markedly in the past decade, particularly in Canine Penile, Preputial, and Scrotal Tumors
the United States, where the value of PSA as a reliable biomarker
has been debated. 219,260 Where much emphasis is placed on early Multiple tumor types can affect the soft tissues of the canine penis,
detection in most tumor types, there has been a dramatic decrease prepuce, and scrotum, including transmissible venereal tumor
in the screening for PCA owing to the increased treatment of (TVT), SCC, sebaceous gland adenoma, mesothelioma, papil-
clinically insignificant tumors, which increase morbidity and mor- loma, lymphoma, plasma cell tumor, mast cell tumor, heman-
tality compared with that associated with natural cancer progres- gioma, melanoma, and fibrosarcoma. 38,280–287 Overall, TVT and
sion. 219,261 Active surveillance is now implemented for many men SCC are the most common neoplasms of the canine penis. Ossi-
with low-risk PCA and screening recommendations have recently fying fibroma, benign mesenchymoma, multilobular osteochon-
been updated to align with other countries. 260–264 After modi- drosarcoma and osteosarcoma can arise from the penile bone (os
fications to the US Preventative Services Task Force (USPSTF) penis). 288–293 Osteosarcoma of the os penis may behave similarly
draft guidelines, the USPSTF, American Cancer Society, Ameri- to other axial skeleton sites with a potential to develop local recur-
can Urological Association, the American Society of Clinical rence after narrow excision and distant metastasis. 288,290
Oncology, the American College of Physicians, and the National Clinical signs are often associated with local disease and
Comprehensive Cancer Network all advocate for patient educa- many dogs present with hematuria, stranguria, or dysuria.
tion and “shared decision making” when considering screening Occasionally, dogs may present with a visible mass and the
high-risk groups, men with a family history, or when other fac- absence of urinary signs; this is likely more common in scrotal
tors may influence the likelihood of nonindolent PCA. 260,261,263 tumors compared with other tumor sites. It is also possible for
Newer PCA biomarker panels may outperform PSA alone as use- clinical signs to be secondary to locoregional or distant metasta-
ful screening tools, especially in high-risk disease. 260,265–267 sis, as the biologic behavior for most tumors is poorly defined.
Well-established and consistent risk factors for PCA in men Full workup and clinical staging, including CBC, serum chem-
are race/ethnicity, family history, and age, although other fac- istry, urinalysis, and thoracic and abdominal imaging, is recom-
tors such as diet and lifestyle may contribute as well. 219,268 mended in dogs with penile tumors before definitive therapy.
Despite the lack of clear evidence for a direct causal role in the Surgical excision is generally recommended and often involves