Breslow Depth (Melanoma)

Key measurement rules (AJCC 8th Edition, CAP protocol): • Start point: Top of the granular layer of the epidermis (the stratum granulosum, just below the stratum corneum). If the epidermis is ulcerated (loss of epithelium), measure from the base of the ulcer (the tumor-air interface), not from the presumed original granular layer. • End point: The deepest continuous or non-continuous tumor cell at the leading invasive front. Include satellite tumor nests, single cells, and tumor cells tracking along adnexal structures (hair follicles, sweat glands, sebaceous glands). Do NOT include inflammatory cells, fibrosis, or non-tumoral melanin-laden macrophages. • Measurement tool: Ocular micrometer calibrated to the objective lens (typically 0.5 mm increments for scanning power, 0.1 mm for high power). Measure perpendicular (vertical) from the start point to the deepest invasive cell using a line perpendicular to the epidermal surface. • Multiple measurements: For tumors with irregular contours, measure from the highest point of the granular layer (or ulcer base) to the deepest invasive cell. In some cases (large desmoplastic melanoma), multiple measurements may be taken; report the greatest thickness. • Microscopic satellites: Tumor nests separated from the main mass by normal tissue (not fibrosis) should be included in the measurement if they are within 0.5 mm of the main invasive front. If beyond 0.5 mm, they are counted separately as microsatellitosis (upstages to N stage, not T).