Complex sentence: This tumor is thought to arise from sebaceous glands in the skin, thus, it may arise anywhere in the body where these glands exist, knowing that the periocular region is rich in this type of gland, so this tumor commonly arise in this region.
Split into simpler sentences: This tumor is thought to arise from sebaceous glands in the skin. Because the periocular region is rich in this type of gland, this tumor commonly arises in this region.