Veterinary Medicine - February 2009 - (Page 78) Canine anal sac adenocarcinoma PEER-REVIEWED 3A. Typical radiation-induced moist desquamation two weeks after completion of 24 fractions of 2.5 Gy to the perineum after incomplete resection of anal sac adenocarcinoma. 3B. The same dog as in Figure 3A one month later showing resolution of the erythema and moist desquamation. De nitive radiation can also be used to treat metastatic lymph nodes that could not be resected at surgery in hopes of decreasing their size and slowing growth for an extended period. In one study, three dogs with anal sac adenocarcinoma had 15 daily fractions of 3.2 Gy of megavoltage radiation therapy to enlarged iliac lymph nodes.7 Two dogs were reevaluated with abdominal ultrasonography: one had complete resolution of the enlarged lymph nodes for two years, and the other dog had one enlarged lymph node that completely responded and another node that reduced in size by more than 50%.7 Complications. Because of the location of anal sac adenocarcinoma and the iliac lymph nodes, many sensitive normal tissues, including the perineal skin, anus, rectum, and colon, may receive unavoidable radiation, and, consequently, side effects can be severe preoperatively and postoperatively. Acute complications that occur during and several weeks after treatment include colitis, tenesmus, moist desquamation of the perineal skin, and perineal discomfort (Figure 3A).7,8 Topical treatments (vitamin E, aloe, commercially available radiation creams), Elizabethan collars, and intensive pain management are required in most cases. Antibiotics may be required to treat secondary skin infections in some patients. Colitis can be managed with ber supplementation and metronidazole. The side effects are typically self-limiting and resolve several weeks after radiation is nished (Figure 3B). Late complications occur months to years after radiation therapy and may present as chronic problems such as chronic diarrhea, chronic tenesmus, rectal stricture, fecal incontinence, and colonic perforation.13 The use of smaller fractions of radiation per dose is associated with a lower risk of these complications.13 Treatment failure is another complication, de ned as regrowth of a tumor or lymph node in the area of previous radiation. In a study of 15 dogs with anal sac adenocarcinoma treated with surgery, radiation, and mitoxantrone chemotherapy, four dogs developed recurrence within the radiation eld.7 Palliative. Radiation can also be used as a palliative treatment in dogs that are not candidates for de nitive treatment with surgery and radiation. Palliative or hypofractionated radiation therapy typically consists of larger doses (6 to 8 Gy) of radiation given weekly for three or four weeks. The goal of this therapy is to provide a good quality of life by reliev- ing clinical signs associated with the anal sac mass or enlarged iliac lymph nodes for a limited amount of time. Palliative radiation therapy is often used in patients with a guarded prognosis due to distant metastatic disease, extensive local disease, or concurrent illnesses. Also, some owners may decline de nitive treatment because of cost, time commitment, or concerns about morbidity. In our experience, partial regression or stabilization of tumor size with alleviation of clinical signs is achieved in about three quarters of cases treated with hypofractionated megavoltage radiation therapy (Figures 4A & 4B). Chemotherapy Chemotherapy has been used for anal sac adenocarcinoma because of the high rates of local metastatic disease and recurrence. The information in retrospective studies can be dif cult to interpret because chemotherapy is often administered along with surgery and radiation or is only administered in dogs with advanced disease, which limits the conclusions that can be drawn about the effect of the chemotherapy. Drugs that have been used include mitoxantrone, doxorubicin, melphalan, cisplatin, carboplatin, 5- uorouracil, mithramycin, vincristine and cyclophosphamide, epirubicin, and actinomycin-D.4-8 78 February 2009 VETERINARY MEDICINE
For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.