Table 2.

Summary of common immunohistochemical stains used in Mohs micrographic surgery for melanoma

Immunostaining antibodies	Cellular targets	Stained cells	Strengths	Weaknesses
S-100	• Intracellular calcium	• Melanocytes • Neural crest derivatives • Histiocytes • Chondrocytes • Lipocytes • Muscle	• Best sensitivity for melanoma • Stain of choice for spindle cell and desmoplastic melanoma • Strong positive staining for deep melanoma components	• Variable staining of epidermis  ○ Problematic for MIS • Poor specificity  ○ High background noise
Human melanoma black-45 (HMB-45)	• gp100 glycoprotein on cytoplasmic premelanosomes	• Immature or proliferating melanocytes • Other cells containing melanosomes	• Greater specificity than S-100	• Less sensitive than S-100 (85%–97%) • Inconsistent staining of pseudonevoid nests  ○ False negatives • Poor staining of spindle cell and desmoplastic melanomas
Mel-5	• g75 pigment-associated glycoprotein on cytoplasmic melanosomes	• Melanocytes • Other cells with melanosomes	• Stains both proliferating and mature melanocytes • Greater specificity and staining intensity than S-100	• Less specific than HMB-45 • Stains nonmelanocytic pigmented cells (e.g., basal epithelial cells, pigmented AKs) • May miss amelanotic or desmoplastic melanomas
Micropthalmia transcription factor (MiTF)	• Transcription factor (nuclear)	• Melanocytes • Schwann cells • Histiocytes • Fibroblasts • Lymphocytes • Smooth muscle	• Great sensitivity and high specificity (88%–100%) • Nuclear staining  ○ Clearly delineates individual cells  ○ Ideal for melanocyte quantification and nucleus diameter measurement  ○ Improves differentiation of chronic sun damage from MIS • Stains epithelioid and spindle cell melanoma • Useful for metastatic melanoma	• Poor staining of desmoplastic melanoma
Melanoma antigen recognized by T cells (MART-1)	• MART-1 glycoprotein on cytoplasmic melanosomes	• Melanocytes • Other cells with melanosomes  ○ Adrenal cortex  ○ Testis, ovary  ○ Retina	• Most useful immunostain • High sensitivity and specificity • Easiest to interpret, crisp staining of melanocytes • Fast immunostaining protocols • Useful for metastatic melanoma	• Does not distinguish benign from malignant melanocytes • Not reliable for desmoplastic or spindle cell melanoma • Severely sun damaged or inflamed skin can lead to false positives
Sry-related HMG-BOX gene 10 (SOX10)	• Transcription factor (nuclear)	• Melanocytes • Schwann cells • Eccrine glands	• High sensitivity and better specificity than MiTF or S100 • Useful for desmoplastic and spindle cell melanoma • Nuclear staining  ○ Clearly delineates individual cells  ○ Ideal for melanocyte quantification and nucleus diameter measurement  ○ Improves differentiation of chronic sun damage from MIS  ○ Useful for metastatic melanoma	• Does not distinguish benign from malignant melanocytes

Note: Table adapted from information presented by Miller et al,³⁶ Hui et al,⁸ Kwon and Miller,³ and Ferringer.⁸⁷

Abbreviations: MIS, melanoma in situ; AKs, actinic keratoses.