superficial spreading melanoma
Monday 30 October 2006
SSM, superficial spreading melanoma in situ
The superficial spreading melanoma may develop on any part of the body, and at any age. It is particularly common on the trunk in males and the lower extremities in females. The umbilicus is a rare site.
It has a shorter radial growth phase than lentigo maligna melanoma and is usually at least superficially invasive at the time of presentation. It also has a variegated color with an irregular expanding margin.
An amelanotic variant has also been reported; rarely, it may clinically simulate a patch of vitiligo.
Areas of regression are not uncommon in both this type of melanoma and the lentigo maligna form.
Superficial spreading melanoma can be regarded as potentially clonally unstable with two or three distinct proliferating tumor cell stem lines in nearly half of the cases tested.
Superficial spreading melanoma is characterized by a proliferation of atypical melanocytes, singly and in nests, at all levels within the epidermis. This pagetoid spread within the epidermis is sometimes known as ‘buckshot scatter’.
Cramer has expressed the view that there is no evidence to support the traditional viewpoint that pagetoid infiltration and pseudoinfiltration are active processes.
Superficial adnexal epithelium may also be involved.
Consumption of the epidermis is present in approximately 40% of cases of malignant melanoma of all types but only in a small number of cases with a benign diagnosis.
It is defined as thinning of the epidermis with attenuation of basal and suprabasal layers and loss of rete ridges adjacent to collections of melanocytes.
It appears to be a precursor to ulceration. It may be a useful clue in the distinction between a melanoma and a Spitz nevus.
Cleft formation is a related phenomenon.
Cramer has suggested that it is a reflection of aberrant melanocyte–keratinocyte interactions.
The infiltrative component may be arranged in solid masses or may have a fascicular arrangement.
The cells may be epithelioid, nevus cell-like, or even spindle-shaped without evidence of maturation during their descent into the dermis. Again the degree of cytological atypia varies from case to case.