Cytopathology is the study of disease on a cellular level.  A common application of cytopathology is the Pap smear used as a screening tool to detect precancerous cervical lesions and prevent cervical cancer Cytopathology is also commonly used to investigate thyroid lesions, salivary gland lesions, lung lesions, or other diseases involving sterile body cavities. Cytopathology is generally used on samples of free cells or tissue fragments in contrast to histopathology which studies whole tissues. Cytopathologists may implore a method known as “Fine Needle Aspiration” in which a small caliber needle is inserted into a lesion either by palpation or with radiographic guidance, and a minute sample is removed for microscopic evaluation.