Aspirates of an anal-sac mass can confirm the presence of a tumor. The cells typically are polyhedral and have uniform round
nuclei (Photo 3). Given that these tumors are epithelial in origin, the cells are found in clusters. The cytologic features
of anal-sac tumors can be relatively benign because they lack many of the typical features of malignancy. However, this appearance
is misleading, given the potential for invasion and early metastasis.
Photo 3: Cytology of an anal-sac tumor at 1000x. (Photographs courtesy of Dr. Kim L. Cronin)
Routine staging for anal-sac tumors should include a CBC, chemistry profile, abdominal ultrasound, abdominal radiographs and
thoracic radiographs. Abdominal ultrasound is more sensitive in identifying the presence of regional lymph-node metastasis
as well as evaluating the liver and spleen for metastatic disease. Abdominal radiographs can detect metastasis to the sublumbar
lymph nodes in some patients and can be used to identify bone lysis in the lumbar region. Bone lysis can be secondary to local
osteolysis from metastatic disease in the sublumbar lymph nodes or from metastatic disease to the bone (Photo 4).
Photo 4: Cytology on an anal-sac tumor at 500X. Note that the cells are well differentiated and have few features of malignancy.
(Photographs courtesy of Dr. Kim L. Cronin)
Treatment outcome can be influenced by several factors, including tumor size, presence of hypercalcemia and the presence of
distant metastasis. For dogs with tumors <10 cm, the survival time was 584 days, while for dogs with tumors >10 cm the survival
time was only 292 days (Williams, 2003).
In the same study, it was found that dogs that were normocalcemic had survival times of 19 months while those with hypercalcemia
lived only 9.6 months. As would be expected, the presence of pulmonary metastasis reduced the survival time from 18 months
to seven months.
Interestingly, the presence of iliac lymph-node metastasis did not affect the overall survival time in this study. This supports
the recommendation to treat dogs with regional lymph-node metastasis aggressively.
The treatment of anal-sac tumors typically involves multi-modal therapy and includes surgery, radiation therapy and chemotherapy.
The first step in treating these tumors is to assess the potential for surgical excision.
Given their location and size, it can be difficult to obtain a wide margin without risk of significant surgical complications
(Photo 5). Complications include wound dehiscence, incontinence and infection.
Photo 5: Anal-sac tumor post-excision. Note the narrow margin.
In hypercalcemia patients, reduction in the tumor burden can reduce or normalize the calcium levels. Dogs treated with surgery
alone have been reported to have survival times of six to 12 months.