Veterinary Medicine - February 2009 - (Page 76) Canine anal sac adenocarcinoma PEER-REVIEWED concentrations and urine speci c gravity in hypercalcemic dogs with anal sac adenocarcinoma is warranted, and treatment of hypercalcemia should be instituted at the discretion of the attending veterinarian. Immediate care may include sodium chloride diuresis along with furosemide. Bisphosphonate therapy may also be considered. Corticosteroids may be used once lymphoma has been ruled out as a cause of hypercalcemia.1 Surgery When technically feasible, surgery is the initial treatment of choice for anal sac alone may not result in normocalcemia. Additionally, enlarged lymph nodes that are not surgically removed will continue to grow and eventually will likely result in obstipation and tenesmus. Two small case series reported lymphadenectomy and excision of the primary tumor in four and ve dogs, with a mean survival of three years in the rst series and a median survival of 20.6 months in the second series; two dogs were still alive at 19 and 54 months.11,12 No surgical complications were noted in any of the cases. Another retrospective study found a signi cant survival advantage self-trauma to the surgical site and be rechecked two weeks after surgery for fecal incontinence or anal stricture. Because of the dif cult location of the tumor and local invasiveness, marginal resection is often performed, and recurrence is common, reported in 45% to 50% of dogs.3,4 Adjuvant treatment is recommended in cases of marginal excision to increase local control and decrease the risk of recurrence. Radiation therapy Radiation therapy can be used preoperatively or postoperatively or palliatively as the sole method of treatment. The lymph node bed may also be radiated prophylactically. adenocarcinoma limited to the primary tumor and local lymph nodes. Surgery may also be indicated in dogs with distant metastatic disease as a palliative measure if the tumor is causing clinical signs. The primary mass should be surgically resected with the intent of complete excision. Because of the tumor’s local in ltration, location, and large size at presentation, an aggressive surgery with wide margins often is not possible. Fecal incontinence is a potential complication, which can be temporary or permanent. Other postoperative complications include wound infection, which can result in dehiscence or sepsis, hypocalcemia, and perianal stula formation.3,8 Early surgical intervention is important, as the masses can be fast-growing, and a window of opportunity may be missed if the mass becomes inoperable. In dogs with hypercalcemia, even incomplete resection can lead to normalization of calcium concentrations postoperatively.3 If the iliac lymph nodes are enlarged, an exploratory laparotomy should be performed for assessment and resection if possible. In cases of hypercalcemia, the tumor cells within the lymph node can secrete PTH-rP, so primary tumor resection in dogs with anal sac gland carcinoma that underwent primary tumor removal and lymph node removal compared with dogs whose metastatic lymph nodes were not removed.6 The lymph nodes may be easily resected in some cases, but they can also be friable and invade the large blood vessels that surround them. Referral to a board-certi ed surgeon is advised for lymphadenectomy because of the dif cult location and potential complications. Fatal hemorrhage is possible, and neurologic damage can lead to transient or irreversible urinary incontinence.3,4 In a few cases in which complete resection is possible, adjuvant treatment may not be required to attain long-term survival, but more data are needed to determine whether recurrence or metastasis develops in dogs treated with surgery alone.6 Routine postoperative management includes patient-appropriate analgesia with opiates and nonsteroidal anti-in ammatory drugs. Hypercalcemia usually resolves within 24 hours. Food can be introduced within eight to 12 hours of surgery, and a stool softener can be added to the food for two or three weeks. The dog should wear an Elizabethan collar to prevent Preoperative. The goal of preoperative radiation is to kill tumor cells existing as microscopic extensions at the tumor periphery, which increases a surgeon’s ability to obtain clean margins. Radiation may also shrink the tumor, thereby increasing the ease of surgical resection. The total dose delivered to the region is decreased in preoperative radiation to prevent healing complications with the intended future surgery. At our hospital, preoperative megavoltage radiation therapy consists of 22 daily fractions of 2.5 Gy, compared with 24 daily fractions of 2.5 Gy for postoperative radiation. Surgery can be performed when the acute radiation side effects have healed, typically within two to four weeks. Postoperative. Postoperative radiation is used in cases in which clean margins are not obtained with surgery. Radiation is started at suture removal, when the surgical incision has healed, and is administered over a course of three to ve weeks. Radiation to the lymph node bed should also be considered after iliac lymph node resection in which disease breaches the capsule since a margin of normal tissue cannot be obtained in this location. The lymph node bed may also be radiated prophylactically in patients that did not have enlarged lymph nodes at presentation since that is the most common location for the development of future metastatic disease.7 76 February 2009 VETERINARY MEDICINE
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