What determines whether a melanoma is classified as invasive?

The classification of melanoma as invasive is primarily determined by the depth of skin penetration. Invasive melanoma is defined by how deeply the cancerous cells have invaded the skin layers, particularly the dermis and beyond. This depth is measured using the Breslow thickness, which quantifies the distance that the melanoma has penetrated from the surface of the skin down to the deepest point of tumor cell involvement.

Melanomas can range from thin, in situ lesions that are not invasive, to thick, invasive tumors that can spread and metastasize. Understanding the depth of invasion is crucial, as it correlates with the aggressiveness of the disease and helps inform treatment decisions and prognostic outcomes. In contrast, characteristics such as color change, size of the lesion, and metastasis to other organs, while important in assessing overall disease progression and management, do not define the initial classification of a melanoma as invasive. Thus, depth of skin penetration remains the definitive criterion.