I'm sorry that your question wasn't answered in a timely manner, Phyllis. First of all it's important that an anal sac adenocarcinoma be differentiated from a perianal adenoma/adenocarcinoma. Anal sac adenocarcinomas are very aggressive tumors which are likely to have already metastasized by the time of diagnosis. They require wide surgical exicision and a search for metastases is essential prior to such extensive surgery because obvious metastases might preclude such surgery. Ancillary chemotherapy is usually recommended for these cancers. Do you know if your dog's tumor involves his anal sac or is the tumor involving only his anus - a perianal adenoma/adenocarcinoma?
A perianal adenoma, however, might result in full or partial tumor regression if an intact male is castrated. Tumors that persist after castration should be removed surgically. For histologically confirmed perianal adenocarcinomas, however, wide surgical resection is indicated.
Biopsy is usually performed after surgical excision which avoids having to anesthetize your dog twice - once for a biopsy and a second time for surgical excision. Here is a summary of the prognosis and outcome for perianal adenoma/adenocarcinoma:
1) For benign perianal adenomas, prognosis is excellent.
2) Adenocarcinomas can recur locally and have a 16% metastasis rate. Tumors larger than 5 cm in diameter are more likely to recur and those dogs are more likely to die of their disease.
3) The prognosis worsens with lymph node/distant metastasis.
4) For dogs with adenocarcinomas less than 5 cm in diameter and greater than 5 cm in diameter without evidence of metastasis, the median survival is 24 and 12 months, respectively.
5) For dogs with adenocarcinomas that exhibit evidence of local or distant metastasis, the median survival is 7 months.
Please respond with the additional information and further questions or concerns if you wish.