Melanoma acrolentiginousC43.7 / C43.7

Location-specific growth type of malignant melanoma growing on the palms of the hands and soles of the feet, fingers, toes and under the nails. Acral lentiginous malignant melanoma grows flat horizontally for a long time, often unnoticed or misrecognized, before it becomes recognizable as a tumor nodule by a vertical change in growth. Not infrequently, advanced melanoma of the acrolentine type lacks the "signal color black" so that the node can appear "inconspicuous" reddish or yellow-reddish. This is especially true for ulcerated acrolentiginous melanomas.

ALM accounts for about 4-5% of the total melanoma incidence, and subungual ALM for 1-3%. From this, incidence rates between 0.2-0.3/100,000 inhabitants can be calculated.

Among acrolentiginous melanomas, the subungual/interdigital group is the most diversified, with oncogenic mutations in the PIK3CA, STK11, EGFR, FGFR3 and PTPN11 genes. They are less likely to have BRAF mutations and show a higher frequency of copy variations (67%!) especially in CDK4 and cyclin-D1. (Haugh et al. 2018)

Elderly people > 60 years. No gender specificity!

Differently large, brown to black, blotchy or plaque-like skin changes.

Horizontal-radial, later circumscribed or diffuse vertical growth with infiltration of the dermis and increasing contouring, nodular, scaly elevations. Superficial erosions, ulcerations.

The clinical maximum variant is a weeping, bleeding tumour node surrounded by a thickened corneal layer.

Other ALM grow for years in a horizontal direction, remain clinically as flat plaques, almost at the skin level, usually with regressions, so that anular or circulatory structures can develop which no longer have structural commonality with the primary image. Complete regressions are also possible.

• The subungual malignant melanoma shows an independent clinical morphology. Although it is a subtype of acrolentiginous malignant melanoma, it is treated independently and as a subungual malignant melanoma.
• Reflected light microscopy: Initially striped, irregular pigmentation, orienting along the inguinal lines, brown, blurred spots in the tumor surroundings.

The prognostic indicators are by far not as precisely determinable as in malignant melanomas of other localizations, since the Breslow index in acral localized melanomas often conveys imprecise values or cannot be assessed at all.

In follow-up studies of metastatic thin melanomas (tumor thickness < 0.75 mm s. Breslow index), the ALM and LMM were significantly overrepresented.

Acral lentiginous melanomas tend to have superficial horizontal growth initially and for long periods. As they are often clinically diagnosed late, they are frequently diagnosed and treated at an advanced stage.

The expression of c-Kit plays an important role in the therapy of metastatic acrolentiginous melanoma (see imatinib below).

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2. Baumert J et al (2009) Time trends in tumour thickness vary in subgroups: analysis of 6475 patients by age, tumour site and melanoma subtype. Melanoma Res 19:24-30

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