+w(200))
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 (Lloyd, KM (2006)) 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 (Lloyd, KM (2006)). 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.
Examples of the clearing zone around melanomas:
| 
