Page 492 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

470 PART IV Specific Malignancies in the Small Animal Patient

margins are recommended for perianal adenocarcinomas because is relatively successful with respect to disease control. The rate of
of their propensity for local recurrence after more conservative metastasis at diagnosis is 15% and is a poor prognostic factor for
576
The MST for dogs with LN or distant metastasis was
survival.
574
Castration is also recommended in intact male dogs
resections.
VetBooks.ir with perianal adenomas because of the role of testosterone in the 7 months; however, aggressive treatment was not attempted in five
569,587
In a smaller study, tumor recurrence occurred in
of six dogs.
576
For diffuse or large perianal
tumorigenesis of these tumors.
adenomas located on or in the anal sphincter, staged surgery may 75% of dogs; however, tumor size, surgical approach, and com-
be preferable with castration initially to decrease tumor volume pleteness of excision were not reported. 574
followed by surgical resection when the perianal adenoma is small If present, regional LN metastasis may be resected and this
enough that it can be more easily and safely resected. More than may result in improved ST. The use of RT and/or chemotherapy,
90% of male dogs will be cured with castration and local resection including actinomycin D, has been reported anecdotally, but their
of the perianal adenoma. 558,569 role in local or distant control is undefined. 576,594,595 Nuclear
Cryosurgery and carbon dioxide laser ablation are possible size, as measured by computer-assisted image analysis in cytologic
alternative treatment options for perianal adenomas, especially tumor samples, and Ki67 expression may correlate with biologic
if small, 588,589 but the major limitation of these techniques is an behavior of perianal adenocarcinoma. 574,596
inability to assess the surgical margins for the completeness of exci-
sion. Hyperthermia and RT have also been used successfully. 590,591
The cost, added morbidity, and limited availability of these modali- Apocrine Gland Anal Sac Adenocarcinoma
ties make them a poor alternative to standard surgical resection.
Electrochemotherapy has been described in dogs with peri- and Other Tumors of the Anal Sac
anal adenoma and consists of intratumoral injections of chemo- Incidence and Risk Factors
therapy followed by local delivery of electric pulses to potentiate
drug uptake by tumor cells. 587,592 Treatments are delivered in AGASAC accounts for 17% of perianal malignancies and 2%
1 or 2 weekly sessions. Based on limited studies, the reported of all skin and subcutaneous tumors. 568,597 Spaniels, particularly
overall response rate is greater than 90%, with 65% complete English cocker spaniels, German shepherds, Alaskan malamutes,
responses. 587,592 Smaller tumors (<5 cm) generally respond bet- and dachshunds have been reported to have an increased risk of
ter than larger tumors. 587,592 Larger tumors are more likely to AGASAC. 598–601 A female predilection was reported in earlier
develop local complications, including focal necrosis, erythema, studies 601–604 ; however, an approximately equal sex distribution
and inflammation. 587,592 Systemic effects are not reported. 587,592 has been shown in multiple larger series. 598–601,605 Neutering
Perianal adenoma may also regress after estrogen therapy 575 ; how- may be associated with increased incidence of AGASAC in male
ever, its use is associated with a risk of myelosuppression. Cyclo- dogs. 598 The mean age of dogs at diagnosis of AGASAC is 9 to
sporin is reported to have had a palliative effect in one dog with 11 years. 568,599–606 Tumors in dogs as young as 5 years have been
multiple ulcerated perianal adenomas and a measurable reduction reported, suggesting that evaluation of the perineum and palpa-
in tumor size was observed. 593 tion of the anal sacs should be a routine part of the physical exami-
Perianal sebaceous gland adenocarcinoma is more locally inva- nation of every adult dog.
sive and generally does not respond to castration. 569 Aggressive AGASAC is a rare tumor in the cat, representing 0.5% of all
surgical resection with a minimum of 1-cm lateral margins is feline skin and subcutaneous neoplasms. 565 The median age of
recommended. Removal of one-half or more of the anal sphinc- affected cats is 13 years, although animals as young as 6 years have
ter is possible with only rare transient loss of fecal continence. been reported. 565,566 Siamese cats may be at higher risk. 565,566
Preoperative incisional biopsy is recommended to differentiate
perianal adenoma from adenocarcinoma because this differentia- Pathology and Natural Behavior
tion may not be possible based on history, gross tumor charac-
teristics, or cytology. If an excisional biopsy is performed, then AGASACs are distinct from perianal gland adenocarcinomas
there is a risk of incomplete histologic excision and local tumor histologically and clinically. Histologic patterns of tumor cell
recurrence. The rate of local tumor recurrence is unknown after arrangement in AGASAC have been classified as solid (closely
incomplete histologic excision, but further surgery is complicated packed neoplastic cells in lobules or nests with minimal stroma),
by the regional anatomy with a greater risk of treatment-associated tubules/rosettes/pseudorosettes (cells are radially arranged around
morbidity. Adjuvant RT may improve local tumor control after a central tubule or a collection of cytoplastic processes or a small
incomplete excision; however, data for this approach are lack- blood vessel), and papillary (elongated tree-like projections with a
ing. The use of electrochemotherapy has been reported in a small fibrovascular stalk). 607,608 The solid and tubules/rosettes/pseudo-
series of dogs. 587,592 Favorable outcomes have been reported, but rosettes patterns occur in about 95% of cases. 607,608
additional clinical studies are needed to validate the efficacy of AGASACs are usually unilateral, although bilateral AGASACs
electrochemotherapy. 587,592 have been reported. 564,603–606,609–611 The overall incidence of bilat-
eral AGASACs, either simultaneously or temporally separated, is
Prognosis up to 14%. 603,604,606,611,612
Paraneoplastic hypercalcemia is reported in 16% to 53% of
The vast majority of dogs with perianal adenoma are cured with dogs with AGASAC. 564,581–602,605–607,609,613–617 Hypercalcemia is
surgical resection and, if indicated, castration. 558,561 Serum VEGF caused by the synthesis and secretion of parathyroid hormone–
levels may correlate with biologic behavior of this tumor type. 576 related peptide from neoplastic tissue. 618–620 Hypertrophic oste-
In a series of 41 dogs with perianal adenocarcinoma, stage of opathy in association with pulmonary involvement has been
tumor had a significant influence on DFI and overall survival reported in two dogs. 621,622 Metastasis is common in dogs with
times (OSTs). 576 Tumors less than 5 cm in diameter (T2) were AGASAC. Overall, metastasis is reported in 26% to 96% of dogs
associated with 2-year tumor control rates in excess of 60%, 576 at the time of diagnosis, with 26% to 89% of dogs having metas-
suggesting that surgical removal of these masses at an early stage tasis to the regional LNs and 0% to 42% with metastasis to distant