Regression of Melanomas
Tumor regression in pigmented lesions is a most interesting phenomenon occurring in both benign and malignant lesions. It basically represents an immune response to a cellular process no longer considered or recognized as essential or desirable. Molecules of the “foreign” material are carried by dendritic macrophages to regional lymph nodes where killer T-cells are activated to destroy the unwanted substance.
As this process progresses, the pigmented lesion starts to regress both in substance and color. Over time the lesions may completely disappear leaving no evidence they ever existed. Examples abound for many of the pigmented melanocytic nevi found on children and young adolescents. This process can be quite dramatic clinically as in the case of halo nevi or the targetoid nevus, or occur so subtly that the individual patient is completely unaware of the process.
Examples of targetoid nevi:
In the case of malignant melanomas, the process is usually partial with areas of the tumor undergoing regesssion with loss of substance and pigment while other areas of the tumor are expanding and increasing in tissue mass. It is important to recognizes areas of regression when present in these tumors clinically. Occasionally, all clinical evidence of the melanoma disappears except for a pigment smudge or faint surface irregularity or scar to mark its’ original location. Metastases to lymph nodes or internal organs may be the first clinical evidence of the disease.
Examples of regression resulting in a “smudge” appearance:
Another useful clue to the presence of a melanoma is what I refer to as the Clearing Zone. It is a fairly well demarked area around the circumference of a melanoma in which the normal evidence of sun damaged skin (telangiectatic blood vessels, ephelides and lentigenes) has disappeared. When seen, it is presumptive evidence the lesion is malignant.