Treatment (ACVS)

Consultation with your primary care veterinarian may result in a referral to a veterinary surgeon to fully explore your options.

• Surgery is the mainstay of treatment. It is the only proven method to influence survival of dogs with these tumors.
  • The tumor is removed through an incision adjacent to the anal opening directly over the tumor.
  • Wide and aggressive removal is not feasible due to the adjacent rectum and anus.
  • With large tumors, additional tissue attached to the tumor may need to be removed. This may result in some of the complications.
• If there are enlarged lymph nodes in the abdomen, they are removed through an abdominal surgical approach on the underside of the dog.
  • These nodes are enlarged in about 50% of cases.
  • This can be done at the time of the primary tumor removal, shortly thereafter, or later if these nodes enlarge.
  • This procedure is done to alleviate the constipation and difficulty defecating.
• If kidney failure or hypercalcemia is present, therapy with intravenous fluids and medications may be needed prior to surgery to make your dog a more suitable candidate for anesthesia. In some cases, kidney failure can be permanent.
• After surgery, chemotherapy and/or radiation treatment may improve the life expectancy of your pet. (ACVS)

How is it Treated? (Cornell)

Dogs with hypercalcemia may need to be stabilized with intravenous fluids and medications, such as corticosteroids or diuretics. 

• Surgery to remove the mass and the entire anal sac (anal sacculectomy) is the treatment of choice. Complete removal can be challenging for larger masses due to their proximity to the rectum. One of the major complications of surgery is fecal incontinence, which may be temporary or permanent. Other complications include infection, poor wound healing and anal stricture.
• If enlarged lymph nodes are present, they can be removed via a separate approach through the abdominal wall. This can be a complicated procedure, and it carries risks of severe hemorrhage and nerve damage that can result in temporary or permanent urinary incontinence. The overall complication rate is approximately 10%.
• Radiation therapy may be used preoperatively, intraoperatively or postoperatively on the anal sac mass and the lymph nodes — reducing the risk of recurrence in cases where complete removal is not possible. It can also be used palliatively in cases where surgery is not an option. Complications, including life-threatening ones, can occur. 
• Chemotherapy has not been proven to improve survival, but may provide some benefits, especially when combined with radiation therapy.
• Palliative care will include pain medications, such as nonsteroidal anti-inflammatories (NSAIDS), corticosteroids (not if NSAIDS are being used), fluid therapy and diuretics. (Cornell)

Chemotherapy (Improve Vet Practice)

Chemotherapy, targeted therapy, RT (radiation therapy) or combinations of these treatment modalities can be considered in cases where surgical management is not possible or not elected by the owner, or in cases of stage IV disease.

• The two main chemotherapy drugs with demonstrated efficacy in the gross disease setting include carboplatin (33 percent partial response rate) and actinomycin-D (50 percent partial response rate), although it should be noted that these figures come from very small study populations (Bennett et al., 2002; Hammer et al., 1994).
• Targeted therapy with toceranib phosphate (Palladia) is perhaps a more promising medical option for the management of gross disease, with clinical benefit seen in 69 to 88 percent of cases (Heaton et al., 2020; London et al., 2012); around 20 to 25 percent of dogs will demonstrate a partial response with 60 to 70 percent achieving stable disease.
  • A clinical benefit is also observed in the majority of stage IV patients, despite no partial or complete responses being observed in one study (Elliott, 2019).
  • Toceranib inhibits a number of targets including VEGFR-2, PDGFR-ß, KIT, FLT3 and CSF1R, a number of which are known to be expressed in canine AGASAC as discussed earlier (Urie et al., 2012).
• Regarding RT, in the gross disease setting response rates of up to 75 percent have been reported, and resolution of hypercalcaemia has been reported in 31 percent of cases (McDonald et al., 2012).
• A variety of protocols, both definitive-intent and palliative-intent, have been described and can be tailored to patient and client needs. In some specific situations, such as stage IIIb disease, RT may be superior to surgery (Meier et al., 2017). (Improve Vet Practice)