A biopsy (in Greek: bios = life and opsy = look/appearance) is a medical test involving the removal of cells or tissues for examination. The tissue is generally examined under a microscope by a pathologist, and can also be analyzed chemically (for example, using PCR techniques). When only a sample of tissue is removed, the procedure is called an incisional biopsy or core biopsy. When an entire lump or suspicious area is removed, the procedure is called an excisional biopsy. When a sample of tissue or fluid is removed with a needle, the procedure is called a needle aspiration biopsy.
Biopsy specimens are often taken from part of a lesion when the cause of a disease is uncertain or its extent or exact character is in doubt. Vasculitis, for instance, is usually diagnosed on biopsy. Additionally, pathologic examination of a biopsy can determine whether a lesion is benign or malignant, and can help differentiate between different types of cancer. In contrast to a biopsy that merely samples a lesion, a larger excisional specimen called a resection may come to a pathologist, typically from a surgeon attempting to eradicate a known lesion from a patient. For example, a pathologist would examine a mastectomy specimen, even if a previous nonexcisional breast biopsy had already established the diagnosis of breast cancer. Examination of the full mastectomy specimen would confirm the exact nature of the cancer (subclassification of tumor and histologic "grading") and reveal the extent of its spread (pathologic "staging").
In an excisional biopsy, the margins of the specimen may be carefully examined to see if the disease has spread beyond the area biopsied. "Clear margins," or "negative margins," means that no disease was found at the edges of the biopsy specimen. "Positive margins" means that disease was found, and additional treatment may be needed.