Let’s start at the moment you are getting your skin checked at your dermatologist’s office. If everything looks normal, your doctor will send you on your way. But if a lesion or mole looks suspicious, your doctor will biopsy it, which means s/he will numb the area and cut out some or all of the suspicious lesion.

You will go home with a bandage on the wound, but where does your piece of skin go?

In most cases, your skin is placed in a labeled jar of liquid formalin (a preservative) and sent to a nearby lab. That lab is often—and hopefully—that of a dermatopathologist. A pathologist is a physician who diagnoses disease through laboratory tests and evaluation of cells, tissues, and organs. A dermatopathologist specializes in skin pathology, a subspecialty of dermatology and pathology. Dermatopathologists are highly trained physicians who complete a residency in either dermatology or pathology and then undergo further training in dermatopathology. They are skin pathology experts, and they are the most qualified to look at your biopsied tissue and determine the correct diagnosis; for example, they will decide if it is melanoma or not.

When your tissue arrives at the lab, a technician prepares it for viewing, a process that includes embedding the tissue in a block of paraffin wax, slicing it in extremely thin sections, and placing the sections on glass slides. The slides are then stained with chemicals that allow the different tissue cells to be identified when viewed under a microscope. The dermatopathologist will then view the glass slides with a microscope and look for indications of skin disease such as melanoma. Challenging cases may receive “immunostaining,” a process that helps the dermatopathologist decipher what types of cell they are looking at. If the dermatopathologist is unsure of the diagnosis, s/he will call on a colleague—or two—to view the slide and give their opinion. Melanoma can be difficult to interpret, and the notes from the dermatologist as well as any pictures that might have been taken are reviewed in conjunction with the tissue under the microscope.

The dermatopathologist will then write a report about the findings, called a pathology report. This report is written primarily for your physician, giving technical information about the findings and the medical conclusion. In the case of melanoma, the report will give details such as the thickness of the tumor and the type of melanoma. The report will also give details related to the American Joint Committee on Cancer (AJCC) staging system. The AJCC system assigns a stage based on tumor, node, metastasis (TNM) scores and other prognostic factors. Once the values for T, N, and M have been determined, they are combined to assign an overall stage in the 0-IV Roman numeral system.

The pathology report will be sent to your physician, and s/he will review the results with you. If the finding is melanoma, your pathology report will note what tumor stage (T) your melanoma is deemed to be. In nearly all cases of a biopsy of a skin lesion, your clinical stage will be designated either Stage 0, Stage I, or Stage II, because the tissue sample cannot reveal lymph node involvement (Stage III) or distant metastases (Stage IV).

Think of it this way: A dermatopathologist is a specialist you “see” without even knowing it. They are physician experts in skin pathology who review the notes on your case and study your tissue. They often call your doctor to get more information about you and the biopsy site, all to help them determine your diagnosis.