Melanoma In Situ, Nos
Soheil Sam Dadras, MD, PhD
Olubukola Babalola
David Cassarino, MD, PhD
Key Facts
Terminology
In situ melanoma that cannot be neatly categorized as well-recognized type of MIS such as lentigo maligna or superficial spreading type
Microscopic Pathology
Asymmetric, poorly circumscribed atypical junctional melanocytic proliferation
Single atypical melanocytes with lentiginous spread and pagetoid upward scatter
Peripheral trailing off of single atypical cells
Spitzoid features may be present in some cases
Cells are markedly enlarged and atypical to bizarreappearing
Top Differential Diagnoses
Melanoma in situ, superficial spreading type
Melanoma in situ, lentigo maligna type
Atypical (dysplastic) junctional melanocytic nevus
Irritated/traumatized nevi and nevi of special sites
 MIS-NOS shows numerous atypical lentiginous cells  along the junction (similar to lentigo maligna), but there is also focal pagetoid scatter  and irregular nesting  (similar to MIS-SST). |
 Higher power magnification shows a predominantly lentiginous proliferation of atypical cells along the junction, with bridging across rete ridges  and limited pagetoid upward scatter of a few cells  . |
TERMINOLOGY
Abbreviations
Melanoma in situ, not otherwise specified (MIS-NOS)
Synonyms
Melanoma in situ, unspecified type
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