Biopsy, << BY op see, >> is a medical technique by which living tissue is obtained for examination under the microscope. For example, a doctor may remove a small piece of tissue from a patient’s tumor. This tissue may be frozen immediately and sliced into extremely thin sections. When a pathologist examines the tissue under a microscope, it can be determined whether the tumor is benign (noncancerous) or malignant (cancerous). This information is important to the doctor in deciding how to complete the operation. Malignant tumors tend to invade (grow into) surrounding tissues. If the tumor is malignant, a surgeon often must remove large amounts of tissue surrounding it in order to be sure of complete removal of the tumor cells. But if the tumor is benign, doctors usually remove only the tumor. See Tumor .
Biopsy also serves as an aid to the diagnosis of certain diseases. In these diseases, characteristic kinds of cells appear in specific places in the body. For example, certain diseases cause changes in the appearance of the cells in the lymph nodes (see Lymphatic system ). Lymph nodes can be examined easily, because some of them lie just under the skin. Doctors may also obtain tissue for microscopic examination by scraping epithelial tissues (the tissues that line the surfaces of the body cavities). They may obtain bits of tissue from structures, such as the liver or kidney, deep inside the body by using a hollow needle. Cells from bone marrow (soft spongy material in the center of bones) can be removed by suction through the needle. Specific diseases are indicated by the presence of certain types of cells in excessive numbers in the marrow.
