What method is primarily used to assess the prognosis of melanoma?

The depth of invasion is the most critical factor in assessing the prognosis of melanoma. This is determined by the Breslow thickness, which measures how deep the melanoma has penetrated into the skin. The thicker the melanoma, the higher the likelihood that it has spread to lymph nodes or other parts of the body, thus leading to a worse prognosis. Accurate assessment of depth allows for better staging of the melanoma, which is crucial for determining treatment options and potential outcomes.

Other factors, such as the size of the tumor, color of the lesion, and presence of ulceration, can play a role in the overall evaluation of melanoma, but none are as definitive as the depth of invasion. For instance, while a tumor's size may influence treatment decisions, it does not directly correlate with the biological behavior of the melanoma in the same way that depth does. Similarly, color and ulceration provide information about certain characteristics of the lesion, but the depth of invasion is the primary measure used to determine prognosis. Ultimately, the depth provides a clearer picture of how aggressive the melanoma may be and its potential for metastasis.