Apocrine gland adenocarcinoma of the anal sac: Catch it early to improve prognosis - DVM
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Apocrine gland adenocarcinoma of the anal sac: Catch it early to improve prognosis


Even for those dogs that have sublumbar lymph-node metastasis, surgery still may be an option. For those owners who wish to be aggressive, removal of both the primary tumor and the sublumbar lymph nodes should be considered. Successful excision of the lymph nodes is possible in some dogs, although in others removal is prevented by the tumor vascularity. The most common complication associated with lymph-node removal is hemorrhage. It is not always possible to determine which patients are good surgical candidates through non-invasive means such as ultrasound.

Radiation therapy can be used either as an adjunct to surgery or the primary means of tumor control. As with any tumor, radiation therapy is most effective when the tumor volume has been reduced to a microscopic level. Full-course radiation therapy or curative intent radiation therapy would be recommended as an adjuvant to surgery. This type of radiation therapy involves the use of 15-19 treatments of radiation therapy given over a three-week to six-week period. Radiation therapy can be started once patients have reached two weeks post-op.

Photo6: Patient treated with full-course radiotherapy, two weeks post-treatment. (Photographs courtesy of Dr. Kim. L. Cronin)
Given the high rate of regional metastasis to the regional lymph nodes, it is recommended that the sublumbar lymph node bed be irradiated as well, regardless of whether there is measurable disease present. Potential acute side effects from radiation therapy include colitis, moist desquamation and alopecia, although these are self-limiting and will resolve two to four weeks after the completion of radiation therapy (Photo 6).

Late radiation side effects, which occur months to years after the completion of radiation therapy, have been reported and include rectal stricture and chronic colitis. These side effects would not be expected to resolve, but in many cases are manageable with supportive care (i.e., stool softeners).

Radiation therapy has been used to treat patients that are not surgical candidates. Full-course radiation therapy has been used in these patients, although due to the larger tumor volume control rates often are reduced.

Unmasking signs of anal-sac tumors
An alternative course of radiation therapy is palliative radiation therapy, intended to provide symptomatic relief from the tumor. The treatment schedule for palliative radiation may differ among clinics, but typically involves three to five large doses of radiation over one to four weeks.

Patients can experience symptomatic relief with this type of radiation therapy with reduced side effects. Resolution of hypercalcemia and/or tenesmus can be seen after palliative radiation therapy. However, it should be kept in mind that this type of radiation therapy is designed for symptom relief and not tumor control.

Therapeutic approaches

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Given the high metastatic rate, chemotherapy is recommended as part of the treatment plan. The most commonly used drugs include cisplatin, carboplatin and mitoxantrone. In most studies, chemotherapy has been combined with surgery and/or radiation therapy, so the true benefit of chemotherapy is not fully known. In one study, dogs that received chemotherapy alone had significantly shorter survival times (212 days) compared to those treated with a combination of surgery and/or radiation therapy as well as chemotherapy (589 days) (Williams, 2003).

In a second study, cisplatin resulted in a 31 percent response rate for the treatment of measurable disease (Bennett, 2002). Dogs treated with both surgery and chemotherapy had significantly longer survival times than either surgery or chemotherapy alone.


Source: DVM360 MAGAZINE,
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