Clinical meaning
Cutaneous melanoma arises from malignant transformation of melanocytes, the pigment-producing cells in the stratum basale of the epidermis. Melanoma accounts for only 4% of skin cancers but causes 80% of skin cancer deaths due to its aggressive metastatic potential. Melanoma subtypes include: superficial spreading melanoma (70% — most common, radial growth phase with lateral spread before vertical invasion), nodular melanoma (15% — most aggressive, lacks radial growth phase, presents as rapidly growing raised nodule with early vertical invasion), lentigo maligna melanoma (10% — arises on chronically sun-damaged skin in elderly, face/neck, slow progression from lentigo maligna in situ), and acral lentiginous melanoma (5% in Caucasians, most common subtype in darker-skinned individuals — palms, soles, nail beds; Bob Marley died of undiagnosed acral melanoma). Breslow depth is the SINGLE MOST IMPORTANT prognostic factor — it measures tumor thickness in millimeters from the granular layer of the epidermis to the deepest point of tumor invasion. The 2018 AJCC 8th edition staging uses Breslow depth thresholds: T1 (≤1.0 mm), T2 (1.01-2.0 mm), T3 (2.01-4.0 mm), T4 (>4.0 mm). Ulceration upstages the T classification...