Final answer:
A biopsy is the surgical removal of a small piece of living tissue for microscopic examination to diagnose diseases, such as cancer.
Step-by-step explanation:
The excision of a small piece of living tissue for microscopic examination to diagnose diseases such as cancer is called a biopsy. During a biopsy, a tissue sample is removed from the patient and is then examined under a microscope by a pathologist. Pathologists can identify cancer by examining changes in the tissue cells and can classify the cancer based on the type of tissue it originates from, such as carcinomas arising from epithelial cells. Knowing the specific type of cancer, such as small-cell carcinomas versus non-small-cell carcinomas of the lung, is crucial as it can significantly influence the prognosis and treatment plan.