What type of tumor is typically fluid-filled and benign in nature?

A cyst is a type of tumor that is typically characterized as being fluid-filled and benign. Cysts can develop in various tissues and organs throughout the body, and they are often encapsulated by a thin wall or membrane. The fluid contained within a cyst can vary in consistency and may include serous fluid, blood, or other substances, depending on the type of tissue involved and the nature of the cyst itself.

In contrast to benign cysts, adenocarcinomas, fibrosarcomas, and hemangiosarcomas are malignant tumors. Adenocarcinoma originates from glandular tissue and can invade surrounding tissues, leading to serious health concerns. Fibrosarcomas arise from fibrous connective tissue and have the potential for aggressive behavior and metastasis. Hemangiosarcomas, originating from blood vessel endothelium, are also malignant and are known for their rapid progression and tendency to spread to other organs. The distinguishing feature of cysts as benign, fluid-filled structures is what makes them the correct answer in this context.