What is a tumor?

Ajay K. Sahajpal, MD
Transplant Surgery
A tumor is a mass that results from abnormal cell division. It can be both benign or noninvasive like a mole or it can be malignant. Malignant tumors are by definition essentially cancers.
A tumor is a "ball" (collection) of cancer cells large enough to see on a scan or by examination. There are tumors that are very bad called malignant tumors and there are tumors that are not harmful called benign tumors. Tumors can occur anywhere in the body; and depending where they start, they can create problems for the surrounding organs. Tumors that start in the breast are called breast cancer; tumors that start in the lungs are called lung cancer etc... Another name for a tumors is a "Mass." So if you ever see "Tumor" or "Mass" mentioned, then these are referring to the same object. To tell whether a tumor is bad or good depends on what is found from obtaining a biopsy of the abnormality.
Discovery Health

When cells divide at an accelerated rate, they often form a mass of tissue called a tumor. The tumor feeds on nutrients that diffuse through neighboring blood vessels and it can also grow by forming something that is called a tumor angiogenesis (vessel forming) factor. The factor stimulates growth of an independent blood supply for the tumor.