Table 1.

Distinguishing features of Pigmented Epithelioid Melanocytoma (PEM) and Melanoma

Sl no.	Key features	PEM	Melanoma
1.	Clinical presentation
a.	Lesion appearance	Presents as a darkly pigmented, well-circumscribed lesion with variable coloration, including shades of brown, black, gray, and sometimes blue.	Presents as a darkly pigmented, asymmetrical lesion with irregular borders and variable coloration with shades of brown and black. They are usually evolving lesions which change in size, shape or color
b.	Size and Growth	Typically smaller in size and tend to grow slowly over time	Can vary in size and often exhibit rapid growth.
2.	Histopathology:
a.	Cellular Architecture	Proliferation of epithelioid melanocytes with abundant eosinophilic cytoplasm, vesicular nuclei, and prominent nucleoli. No atypia/pleomorphism noted.	May show a wider range of cytologic atypia and pleomorphism.
b.	Mitotic Activity	Lower mitotic rate	Usually higher mitotic rate
c.	Pagetoid Spread	Less common	Often display pagetoid (single cell) spread within the epidermis
d.	Junctional activity	Less common	More common
e.	Lymphovascular Invasion	Less common	More common
3.	Immunohistochemistry
a.	S100	Both PEM and melanoma cells may stain positive for S100 protein, but PEM cells typically show a more diffuse and strong staining pattern.
b.	HMB-45	Positive staining for HMB-45 is common in both PEM and melanoma, but PEM cells may show a more consistent and diffuse staining
c.	SOX10	Positive staining for SOX10 is often seen in both PEM and melanoma, with stronger and diffuse staining in PEM.
4.	Genetic and Molecular Features:
a.	BRAF Mutation	Less frequent	More common
b.	KIT Mutations	Some cases have been associated with KIT mutations	Less common
c.	Cytogenetic Abnormalities	Less prevalent	More prevalent in melanomas
5.	Clinical Behaviour
a.	Metastasis	Less aggressive and can metastasize	More aggressive and have a higher potential for metastasis
b.	Prognosis	Indolent clinical course with good prognosis	Poor prognosis