• Standardized staging for cutaneous melanoma to establish prognosis.
• Basis for directing surgical intervention (e.g., margins, sentinel lymph node biopsy) and adjuvant therapies.

• T (Tumor): Determined primarily by Breslow thickness (measured to the nearest 0.1 mm) and presence/absence of ulceration.
• N (Nodes): Categorized by the number of involved lymph nodes and whether they form a clinically occult (microscopic) vs. clinically apparent (macroscopic) metastasis, plus presence of in-transit, satellite, or microsatellite metastases.
• M (Metastasis): Determined by anatomic site of distant metastasis and serum LDH levels.

• Mitotic rate is no longer used as a staging criterion to differentiate T1a from T1b. Ulceration and thickness strictly demarcate the T1 categories (T1a <0.8mm without ulceration; T1b 0.8-1.0mm OR <0.8mm with ulceration).
• Microsatellite lesions are now grouped with satellite and in-transit metastases as N1c, N2c, or N3c depending on the number of nodes involved.

Pathologic staging (pTNM) requires wide local excision and sentinel lymph node biopsy (typically offered for T1b and above, or T1a under specific risk circumstances). Drives eligibility for PD-1/BRAF adjuvant therapies.