Canine Anal Sac/Gland Adenocarcinoma. Tumors of the anal sac are uncommon a represent a small percentage of all tumors in dogs (<1%). The most common. Anal sac apocrine gland adenocarcinoma is locally invasive and typically affects one anal sac; however, bilateral tumors can occur.4 The metastatic potential is. Anal Sac (Apocrine Gland) Tumors in Dogs and Cats KEY TAKEAWAYS * Anal sac (apocrine gland) tumors can be found by rectal examination.