Aspiration biopsy technique. Illustration of the stages of a fine-needle aspiration biopsy. A needle is inserted (top) into the mass (usually a tumour or other growth) that is being investigated and cells withdrawn. The technique shown here (withdrawing and depressing the plunger) ensures the correct sampling of cells. The cells are transferred to a glass slide (final two stages) to be examined under a microscope to see if the growth is cancerous or benign. The technique is also known as fine-needle aspiration cytology.