Which of the following is a benign mass commonly removed from small animals?

The correct answer is a benign mass that is commonly removed from small animals, which is a sebaceous cyst. Sebaceous cysts are formed from blocked sebaceous glands and are typically filled with a thick, cheese-like substance. They are often benign and may not cause harm to the animal unless they become infected or grow large enough to cause discomfort or other issues.

While lipomas, which are fatty tumors, are also benign and frequently removed, they are specifically characterized by their composition of adipose tissue. They too are commonly found in small animals and may require surgical removal if they interfere with mobility or become painful.

Hemangiosarcoma and osteosarcoma, on the other hand, are malignant tumors. Hemangiosarcoma arises from blood vessels and carries a poor prognosis due to its aggressive nature, while osteosarcoma primarily affects bone and is known for its invasive behavior. These conditions necessitate more extensive treatment due to their potential to metastasize and resulting risks to the animal's health.

Thus, the selection of a sebaceous cyst aligns with the definition of benign masses that are often surgically removed from small animals.