Melanoma Grading

Two sourcing tiers

Modules A–C (Breslow thickness, AJCC T-category, Clark level) are built from a supplied CAP/AJCC protocol excerpt, which cites the 8th edition of the AJCC melanoma staging system — consult the current AJCC Cancer Staging Manual (melanoma chapter) directly.

Module D (mitotic rate) is built from standard, well-established published AJCC/CAP methodology rather than a pasted excerpt — confirm against your institution's current protocol before clinical use.

Measurement technique

Maximum tumor thickness is measured with a calibrated ocular micrometer at a right angle to the surface of the lesion at the point of measurement.

Upper reference point: the upper edge of the granular layer of the epidermis of the overlying skin (if intact), or the base of the ulcer, if the lesion is ulcerated.

Lower reference point: the deepest point of tumor invasion — the leading edge of a single mass or an isolated group of cells deep to the main mass.

For melanomas lacking an intraepidermal component, thickness is measured from the top of the epidermal granular layer to the deepest invasive cell.

Transected deep margin: if the tumor is transected at the deep margin of the specimen, depth may be indicated as "at least __ mm" with a comment explaining the limitation — e.g., "The maximum tumor thickness cannot be determined in this specimen because the deep plane of the biopsy transects the tumor."

Periadnexal extension: thickness measurements should not be based on periadnexal extension (adventitial or extra-adventitial), except when it is the only focus of invasion — in which case thickness may be measured from the inner layer of the outer root sheath epithelium, or the inner luminal surface of sweat glands/ducts, to the furthest extent of periadnexal dermal infiltration.

Excluded from thickness: satellites (macroscopic or microscopic) and foci of neurotropism or lymphovascular invasion should not be included in tumor thickness measurements.

Reporting precision & rounding

The AJCC 8th edition recommends thickness be recorded to the nearest 0.1 mm, not the nearest 0.01 mm, due to the impracticality and imprecision of finer measurement — particularly for tumors >1 mm thick. Tumors ≤1 mm may be measured to the nearest 0.01 mm if practical, but are still reported to the nearest 0.1 mm.

AJCC 8th edition T-category

T1 is subcategorized at a 0.8 mm threshold; tumor mitotic rate is no longer used as a T1 staging criterion.

The T1 thickness/ulceration definitions (0.8 mm and 1.0 mm thresholds) are quoted from the supplied protocol excerpt. The T2–T4 thickness bands (>1.0–2.0 mm, >2.0–4.0 mm, >4.0 mm) reflect standard AJCC 8th edition melanoma T-category criteria, which were not themselves included in that excerpt — confirm against the current AJCC Cancer Staging Manual.

Anatomic (Clark) level

Clark level remains an independent predictor of outcome and is recommended by the AJCC to be reported as a primary tumor characteristic. However, assessment of Clark level is less reproducible among pathologists than tumor thickness, and Clark level is not used in the AJCC staging system for pT status — it is included in the source checklist as an optional data item.

Mitotic rate — counting method

Counting begins in the area of highest mitotic activity within the invasive tumor component (the "hot spot"). If no clear hot spot is present, counting begins in a representative cellular area. Counting extends into contiguous fields until a total area of approximately 1 mm² has been assessed; the total mitotic count is then divided by the area actually assessed and reported as mitoses per mm², rounded to the nearest whole number. If any mitoses are identified but the rate rounds to less than 1/mm², it is conventionally reported as 1/mm²; if none are identified, it is reported as 0/mm².

This is standard, widely used mitotic-rate counting methodology (informed by the hot-spot method used in AJCC 7th/8th edition melanoma protocols), not a quotation from a pasted source document. Confirm the exact convention against your institution's current protocol. Mitotic rate is no longer a T1 staging criterion for melanoma in the AJCC 8th edition but remains a widely reported parameter due to its independent prognostic value.