Path report

The diagnosis of melanoma is made with a biopsy. This is a removal, usually in a dermatologist’s office, of all or a portion of the suspicious area on your skin. The biopsy in turn generates a pathology report from the lab, which is the most important thing for you to know about.

If you haven’t done so yet, get a copy of your pathology report. You should start a file with all your melanoma related info. Page one of that file is your pathology report. Keep that and all subsequent pathology reports, from either second opinions or other biopsies) together in the file.

What should you look for on your pathology report?

First, make sure it has your name and birthdate on the top. Make sure there are no errors in your personal information. Make sure the date of the biopsy (specimen date) is correct—if the date is wrong, maybe it’s not your specimen. Make sure the location of the specimen is correct, especially “sidedness” ie left or right, top or bottom, etc. These are all important for the basic “quality control” of your pathology report. With any quality control issue described in this section, if that piece of information is wrong or missing, you should immediately call the lab and/or your doctor on the phone and demand a correction or explanation. I can assure you that my office does it for all our patients to make sure we aren’t missing something important.

Here are the key features of any melanoma, in descending order of importance to your treatment and prognosis:

Thickness or Breslow thickness, measured in mm and fractions of mm

Ulceration

Clark’s level, in roman numerals

Margins (possibly described as lateral, peripheral , deep, base of biopsy, etc.)

Other factors that have a lesser or emerging and variably important influence on prognosis and treatment:

Regression

Vertical growth phase

Sub-type of melanoma

Mitotic rate

Lymphatic or vascular or lymphovascular invasion

The most important prognostic factor in melanoma is the measured “Breslow” thickness, in mm, of the melanoma under the microscope, from the most superficial area to the deepest melanoma seen on the biopsy slides. This is named after the dermatopathologist who described their significance several decades ago. The AJCC staging system (an internationally published standard that correlates, for any cancer, clinical and pathologic criteria with survival and groups these criteria by shared survival outcomes) divides Breslow thickness into various risk levels. Other physicians may use slightly different thickness criteria for risk level assignment.

However, the important thing is that Breslow thickness is a continuously variable and continuously relevant prognostic piece of information. That means that regardless of any other information, the thicker the Breslow measurement is, the riskier the melanoma. Thus, even though (by my criteria) melanomas with Breslow thickness and 2.2 mm and 3.8 mm are both “intermediate risk” and by the AJCC staging criteria both are “T3”, the 3.8 mm melanoma is much higher risk and carries a worse prognosis.

Ulceration refers to a pathologic finding (ie under the microscope) that the top of the melanoma had fallen off, leaving an absence of the top layer or epidermis. This is not the same as shaving or picking off the top of what later proves to be a melanoma—it must be designated ulceration by the pathologist. Since the AJCC stage (and potentially, treatment) changes with the presence or absence of ulceration, all pathology reports should include a mention of ulceration status. In my experience, this is the most important crucial information that pathologists do not include, so this is another quality control check for your pathology report.

Clark’s level is also named after a pathologist and is in some ways an older version of Breslow thickness. It classifies the depth (yes we are distinguishing depth from thickness…) of a melanoma based on the skin structures or components near the deepest part of the melanoma, from Level I through Level V. In general, the Clark’s level correlates with Breslow thickness, but prognosis from melanoma is better correlated with Breslow thickness; thus Breslow thickness is more commonly used and many pathology reports may not report Clark’s level at all. That is fine except in one instance: the Clark’s level is still relevant (provides additional information on prognosis) with Breslow thickness less than 1 mm, and only if the Clark’s Level is IV or greater. Thus for any melanoma of Breslow thickness 1 mm or less, the pathology report should also include a Clark’s level assessment: another quality control measure.

Mitotic rate or mitotic index has recently been assigned greater importance. It is an assessment of how actively the melanoma cells are growing. In general, like Clark’s level, it is most important when the melanoma is relatively thin but the mitotic index is higher than expected (ie Breslow less than 1 mm but mitotic index 1 or more per square millimeter. If the Breslow thickness is greater than 1 mm, the mitotic index is not as important and generally correlates with thickness.

In pathology reports, “margins” refer to the edges of the specimen. Specifically, does the melanoma extend up to any edge of the biopsy specimen? Most of the time, margins are “clear” or “negative”, meaning that the melanoma is completely contained within the biopsy tissue. Other times, the melanoma is found to extend to peripheral or lateral margins, meaning that the malignant cells extend to a sideways edge of the specimen. In my practice, this does not generally change the treatment planning, because experienced dermatologists generally are able to identify the thickest or riskiest part of the melanoma when performing a biopsy. For example, if the suspicious skin lesion is several inches in size, the dermatologist may only biopsy a portion, enough to obtain a diagnosis. Thus when the peripheral or lateral margins (only) are “positive” for melanoma, that usually is enough information to plan treatment. This has been confirmed in recent studies.

However, a positive “deep” margin, which may alternatively be described in the pathology report as “extending to the base of the specimen”, may be much more significant. The reason for this is actually very straightforward: since the most important prognostic factor is tumor thickness, having the tumor extend to the bottom of the specimen suggests that the tumor may have extended beyond the biopsied tissue. The actual tumor thickness could therefore be greater and therefore in those cases I use the measured Breslow thickness as a minimal estimate rather than an absolute measurement. This may change the planned treatment.

The other factors listed, including regression, mitotic rate, lymphatic or vascular invasion, and vertical growth phase, are usually listed in the pathology report as either “present” or “absent”.  The other listed factors are generally present in higher risk melanomas, or at least suggest a riskier profile of a given melanoma. For example, if the only difference between two melanomas with Breslow thickness 0.9 mm is that one has vertical growth phase, it is probable that the one with vertical growth phase has a slightly (very difficult to exactly estimate or measure) worse prognosis. However, a melanoma’s riskiness is most clearly defined by Breslow thickness and ulceration; these other factors contribute to but do not ultimately define the prognosis.

There are several subtypes of melanoma. The most common, probably occurring at least 85% of the time, is called superficial spreading melanoma. The next most common is probably nodular melanoma. More uncommon types of melanoma include acral lentiginous (mostly on the hands or feet), desmoplastic (a pathology term describing the architecture of the cells), and neurotropic (growing along nerves). These occur rarely enough that it is not known if they carry a different prognosis than the more common superficial spreading or nodular sub-types. It is generally felt that the same prognostic factors (ie tumor thickness and ulceration) apply to all subtypes of melanoma, although there is a general impression among melanoma experts that certain subtypes may spread or “behave” slightly differently.

There are also a few subtypes that are extremely low risk. Melanoma in situ means that the skin cells are abnormal, like other melanoma cells, but have not invaded past the usual boundaries of the skin. In situ means “in place” in Latin, referring to the fact that the bad cells do not go beyond where they are supposed to be in the skin architecture. Since the tumor cells have not invaded beyond their natural boundaries, these melanomas (if an invasive area has not been missed) are much less aggressive that true, invasive (Breslow thickness is actually a numeric measurement of invasion) melanomas. Another special type of melanoma is called “Lentigo Maligna.” These are a form of melanoma in situ, and generally have little if any metastatic potential.

Ultimately, the information on your pathology report is used to formulate your treatment plan. It is without a doubt the most important information about your melanoma initially. Make sure you get a copy!


 

Eric D. Whitman, MD
Senior Editor, TheMelanomaCenter.com

(Publisher’s note: Dr. Whitman is currently finishing his first publication, which will expand this discussion on pathology report and give you insider-level knowledge on how to analyze and act on your pathology report and its findings. This e-publication will be available exclusively through TheMelanomaCenter.com. For more information, click here.)

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