Your dog has two anal sacs or scent glands. The anal sacs are small, round glands located just under your dog’s skin next to his anus. The anal sacs are capable of secreting a small amount of liquid which is usually brown or grey and has strong foul odor. This liquid is used by your dog for communication purposes. A small amount of liquid is expelled when your dog defecates and also when your dog is frightened. Most anal sac tumors (adenocarcinomas) originate from cells within the sac and are almost always malignant. In addition, these tumors are known to metastasize or spread.

You will be able to see or feel a firm, enlarged anal sac next to your dog’s anus. Your dog may lick his rear end frequently and may have trouble defecating. Your dog’s stool will likely decrease in size and width due to the tumor.

Anal sac tumors also can cause an irregular elevation of calcium in your dog’s bloodstream. If this is the case, your dog will have a diminished appetite, weakness, vomiting, constipation, and increased thirst and urination.