Melanoma Stages Explained: From In Situ to Stage IV
Melanoma staging determines prognosis and treatment. The stage depends on tumor thickness (Breslow depth), whether it has spread to lymph nodes, and whether it has metastasized to distant organs. Early detection is critical - 5-year survival drops from 99% at stage I to about 35% at stage IV.
Stage 0: Melanoma in situ
Melanoma cells are confined entirely to the epidermis. Also called melanoma in situ or lentigo maligna on sun-damaged facial skin. Treatment is surgical excision with clear margins. Cure rate is nearly 100%.
Stage I: Early melanoma
The tumor has invaded the dermis but remains thin. Stage IA: 1mm or less thick without ulceration. Stage IB: 1mm or less with ulceration, or 1-2mm without ulceration. Treatment is wide local excision. Sentinel lymph node biopsy may be recommended for IB. 5-year survival: 97-99%.
Stage II: Thicker melanoma
The tumor is thicker but has not spread to lymph nodes. Stage IIA: 1-2mm with ulceration, or 2-4mm without. Stage IIB: 2-4mm with ulceration, or over 4mm without. Stage IIC: over 4mm with ulceration. Treatment includes wide excision and sentinel node biopsy. 5-year survival: 80-94%.
Stage III: Regional spread
Melanoma has spread to nearby lymph nodes or has in-transit metastases (tumor deposits between the primary site and regional nodes). Treatment may include complete lymph node dissection, immunotherapy, targeted therapy, or radiation. 5-year survival: 40-78% depending on substage.
Stage IV: Distant metastasis
Melanoma has spread to distant organs - most commonly lungs, liver, brain, bone, or distant skin. Modern immunotherapy (checkpoint inhibitors like pembrolizumab and nivolumab) has dramatically improved outcomes. Before immunotherapy, median survival was 6-9 months. Now, about 40-50% of stage IV patients survive 5+ years with immunotherapy.
Breslow thickness: the key measurement
Breslow depth measures tumor thickness in millimeters from the top of the epidermis to the deepest tumor cell. It is the single most important prognostic factor for localized melanoma. Less than 1mm: thin melanoma, excellent prognosis. 1-2mm: intermediate. 2-4mm: thick, higher risk. Over 4mm: very thick, significant risk of metastasis.
Nodular melanoma and other subtypes
Nodular melanoma grows vertically (downward) rather than spreading horizontally first. It accounts for about 15% of melanomas but a disproportionate share of thick melanomas and deaths because it reaches dangerous thickness faster. Acral lentiginous melanoma occurs on palms, soles, and under nails - the most common subtype in darker-skinned individuals. Amelanotic melanoma lacks pigment, making it harder to detect visually.
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