To begin, a biopsy of the tested area is taken. There are three types of biopsies: Incisional Biopsy, where a portion of the lesion is removed; Excisional Biopsy, where the entire lesion is removed; and Needle Biopsy, where a needle is used to collect tissue samples (commonly performed on organs such as the liver or breast).

Immediately after collection, the specimen is immersed in a fixative solution (usually formalin) to preserve cellular structures. Once fixation is complete the biopsy moves through a series of processes before it is ready to be examined under the microscope.

During processing the tissue is dehydrated to remove water and replaced with an embedding medium (paraffin wax) for slide preparation. The tissue is passed through a series of increasing concentrations of alcohol (e.g., 70%, 80%, 95%, and 100%) to gradually remove water from the tissue.

A clearing agent (like xylene) removes the alcohol and renders the tissue transparent ready for infiltration and embedding.

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