The ABCD rule is a clinical heuristic for distinguishing malignant melanoma from benign melanocytic nevi based on four morphologic features—asymmetry, border irregularity, color variation, and diameter/growth over time—reflecting the underlying pathologic distinction between disorganized malignant proliferation and uniform benign growth. Melanoma is further subclassified into four histopathologic subtypes distinguished by growth pattern and depth of invasion (horizontal/superficial vs. vertical/deep), which determines metastatic risk, and staging relies on lesion depth (Clark's Levels) combined with TNM criteria (tumor size, nodal involvement, metastasis) to predict prognosis. This is a topic within dermatology/dermatopathology and oncology, linking clinical lesion morphology to underlying tumor biology, invasion depth, and prognostic staging.
The ABCD rule is a clinical heuristic for distinguishing malignant melanoma from benign melanocytic nevi based on four morphologic features—asymmetry, border irregularity, color variation, and diamet…