A biopsy of the tested area is taken. There are three methods of biopsies:

Incisional Biopsy: A portion of the lesion is removed.

Excisional Biopsy: The entire lesion is removed.

Needle Biopsy: A needle is used to collect tissue samples (common for organs like the liver or breast).

Immediately after collection, the specimen is immersed in a fixative solution (usually formalin) to preserve cellular structures. When it is ready to be examined and the required time of fixation, for the size specimen, has been met then the biopsy is prepared into a small enough sample to be examined under the microscope.

The tissue is dehydrated to remove water and replace it with a solvent that is miscible with the embedding medium (paraffin wax). 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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