What is the malignant tumor composed of a mass of minute lymph vessels known as?

A malignant tumor composed of a mass of minute lymph vessels is known as lymphangiosarcoma. This type of cancer arises from the lymphatic vessels, which are part of the lymphatic system responsible for transporting lymph, a fluid that is crucial for immune function. Lymphangiosarcoma is particularly associated with chronic lymphedema, which can occur after the surgical removal of lymph nodes or radiation treatment. The condition reflects the malignant transformation of cells within the lymphatic vessels, leading to the proliferation of these cells and the formation of a tumor.

The other options refer to different types of tumors: angiosarcoma involves malignant growths of blood vessels; cystosarcoma is associated with cystic structures; and mesothelioma primarily affects the lining of the lungs and abdomen, often related to asbestos exposure. Each of these tumors has distinct characteristics and origins, further highlighting why lymphangiosarcoma is specifically identified as being derived from lymphatic vessels.