IN SITU ACRAL LENTIGINOUS MELANOMA ARISING IN A NEVUS
It is uncommon to encounter an acral lentiginous melanoma that is not invasive, and the radial growth component of a prototypic acral lentiginous melanoma is larger than this. If the entire specimen had not been submitted for sectioning, the significant area might not have been detected. Confluent radial hyperplasia of intensely hyperchromatic melanocytes having little cytoplasm characterizes the in situ component of this lesion.

A shave type biopsy measuring 1 cm. across was taken from the foot of this 29 year old male. The specimen was trisected and the three pieces submitted for sectioning.
 
 
Scan power view of part of one of the pieces of the specimen.
Low power view of above. This, as was true of much of the specimen, has the features of an ordinary nevus with the exception of some hyperchromatic cells in the rete ridge in the extreme left side of the picture..
Composite low power view of an area that was 5 mm. in width.
Composite medium power view of above. A focus of dermal invasion was not identified in the specimen. There is confluent hyperplasia of intensely hyperchromatic melanocytes in the lower epidermis.
A high power view of above. The intensely hyperchromatic melanocytes in the lower epidermis have little cytoplasm. Some appear to be round, and others are slightly dendritic..
Another high power view. Many of the hyperchromatic melanocytes are triangular, angulated, or dendritic. 

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