Case Number : Case 2892 - 06 August 2021 Posted By: Dr. Richard Carr

Left--> Melanoma, balloon cell type, sprung by a Lentigo Maligna. Right--> nevus. 

Melanoma has an expansive nodular growth and pushes the elastic fibers, while nevus has an infiltrative one, between collagen and elastic fibers. 

Beauty!!

The DD here is balloon cell change in a nevus (with overlying junctional component) vs balloon cell melanoma. Age of the pt, nuclear pleomorphism, lack of (maturation, pigmentation, intervening stroma) and prominent nucleoli favor the 2nd. Also atypical mitosis, if present.

There appears to be expansile nodule with cytological atypia. Loss of p16 in this zone compared to the rest. I would favour nodular melanoma arising in a nevus. 

Looks like a different clone, melanoma (p16 loss) arising in nevus (p16 preserved )

AGREE MELANOMA IN A NEVUS

agree with melanoma in a nevus.  also curious to know what is the BAP-1 status? it does have that BAPoma look of those epithelioid melanocytes with binucleation and lymphocytes response.

Agree with melanoma in a naevus. p16 was helpful for assessing the depth. Nice example of a background Miescher type naevus with exaggerated elastic fibres not seen in the melanoma part. p16 null and a small lateral SSMM were present (not shown) so I did not do BAP1 but agree worth considering in all biphenotypic naevi (although the "sptizoid" component here is a little too pleomorphic with quite irregular chromatin).