This is an extremely simple technique, A syringe with 22 gauge needle which is used to give routine injections is inserted into a lump (tumor), and a few tens to thousands of cells are drawn up (aspirated) into a syringe. The cells are smeared on a slide, stained, and examined under a microscope by the pathologist.
Tumors of deep, hard-to-get-to structures (pancreas, lung, and liver, for instance) are especially good candidates for FNAC, as the only other way to sample them is with major surgery.
Such FNAC procedures are typically done by a surgeon or radiologist under guidance using ultrasound or computed tomography (CT scan) and require no anesthesia, sometimes local anesthesia.
Thyroid lumps are also excellent candidates for FNAC diagnosis. A diagnosis can often be rendered in a few minutes.