A tumor is an abnormal growth of tissue. Tumors can be benign, which means they are not cancerous, or malignant, which means they are cancerous. Benign tumors grow slowly and do not spread to other parts of the body. Malignant tumors grow quickly and can spread to other parts of the body.
Most tumors form in specific organs, such as the brain, breast, or colon. However, some types of tumors, such as lymphoma and leukemia, form in the blood cells or in the tissues that support the blood cells.
Tumors can be either primary or secondary. A primary tumor is one that forms in the organ where it originates (for example, in the breast). A secondary tumor is a metastatic tumor; it forms when cancer cells break away from a primary tumor and travel through the bloodstream to another part of the body and begin growing there (for example, in the lung). Secondary tumors are more common than primary tumors because most cancers have already spread by the time they are diagnosed.
There are many different types of cancer; each type develops from a different kind of cell in the body. The four main types of cancer are carcinomas (cancer that begins in epithelial cells), sarcomas (cancer that begins in connective tissue), lymphomas (cancer that begins in white blood cells), and leukemias (cancer that begins in blood-forming cells).
Cancer is treated with surgery, radiation therapy, chemotherapy, targeted therapy, or immunotherapy. Surgery is used to remove a tumor; radiation therapy uses high-energy rays to kill cancer cells; chemotherapy uses drugs to kill cancer cells; targeted therapy targets specific molecules involved in cancer cell growth; immunotherapy boosts the immune system’s ability to fight cancer.