Tumors are abnormal growths caused by uncontrolled cell division. They are classified as benign or malignant, with malignant tumors being cancerous and able to spread. There are various classification systems, with rating scales describing the aggressiveness of the tumor. Different types of cancer have different classification systems, such as brain tumors being classified by the WHO system and ovarian tumors being classified by the type of cell they originated from.
A tumor is an abnormal growth of tissue that has no physiological function. Tumors are caused by rapid, uncontrolled cell division that keeps expanding without treatment. Cancer classification is a system devised by the scientific and medical community to enable professionals to identify, diagnose and treat cancer.
When a tumor is discovered, the first step in classifying the tumor is to determine whether the growth is benign or malignant. Benign tumors are slow-growing, noncancerous, and localized, meaning they have not invaded other tissue. These growths can usually be removed and won’t come back. Benign tumors can cause serious problems, depending on their size and location, and some, like polyps in the colon, can become cancerous if not removed.
Conversely, malignant tumors are cancerous and have the ability to spread, or metastasize, to nearby tissues and organs. Cancer cells can also break away from tumors and enter the blood or lymph system, spreading the disease to other parts of the body. Malignant tumors require quick and specific treatments, thus they are the main focus of tumor classification.
There is no single system for classifying tumors. Once upon a time, tumors were classified according to how they looked under a microscope; other systems evolved based on where the growth originated and what type of tissue it most resembled. As scientific advances have allowed doctors to observe the different cellular and molecular properties of various cancers, new cancer classification systems have emerged. As a result of these changes, a single type of cancer can have multiple names, while two different cancers can have the same name. If a patient is diagnosed with cancer it is important that he not only knows the name given to him by the pathologist, but also what staging or naming system is being used.
The second part of the tumor classification is a rating scale that describes the aggressiveness and malignancy of the tumor. Most rating scales range from I to IV, with grade I describing a tumor that is slow growing and composed of fairly normal cells. Grade II is slow growing, with slightly abnormal cells and may recur after removal. Grade III is more severe and applies to more active malignancies that are invading nearby tissue. Grade IV tumors are the most critical and consist of rapidly growing, highly invasive malignant cells.
The cancer classification system employed also varies between different types of cancer. For example, brain tumors are now generally classified according to the system recently developed by the World Health Organization (WHO). This system classifies the tumor based on the type of cells present where the tumor originated and the biological behavior of those cells.
Tumor classification for ovarian tumors depends on whether they are benign or malignant and the type of cell in which the tumor originated. Tumors that start on the surface of the ovary are called epithelial tumors. Those that begin in the cells that produce eggs are called germ cell tumors, and tumors that begin in the cells that produce hormones are called stromal tumors.
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