Stains
MelanA / MART1

Author: Yao-Tseng Chen, M.D., Ph.D. (see Authors page)
Deputy Editor Review: Debra Zynger, M.D.

Revised: 17 July 2018, last major update May 2018

Copyright: (c) 2002-2018, PathologyOutlines.com, Inc.

PubMed Search: MelanA[TI] OR MART1[TI]

Cite this page: Chen, Y.T. MelanA / MART1. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/stainsmart1.html. Accessed October 19th, 2018.
Definition / general
  • Melanocyte specific cytoplasmic protein involved in the formation of stage II melanosomes
  • MelanA was discovered as an antigen recognized by tumor infiltrating cytotoxic T cells from a melanoma patient, hence the name Melanoma Antigen (J Exp Med 1994;180:35)
  • Same gene was independently identified by a different research group who named it MART1 (Melanoma Antigen Recognized by T cells 1) (Proc Natl Acad Sci USA 1994;91:3515); MelanA and MART1 are synonyms
  • Two antibodies are commercially available: A103 and M2-7C10
    • A103: mouse monoclonal antibody against MelanA recombinant protein (Proc Natl Acad Sci USA 1996;93:5915, US patent 5,674,749)
      • In addition to melanocytes, A103 also stains adrenal cortical cells and steroid producing cells in testis and ovary
      • This is due to antibody cross reactivity to an unknown molecule in these cells; these cells do not produce MelanA / MART1 mRNA or protein (Am J Surg Pathol 1998;22:595)
    • M2-7C10: mouse monoclonal antibody clone produced against MART1 protein
      • This antibody stains only melanocytes among normal tissues; negative for adrenal cortical cells and steroid producing cells in testis or ovary (J Immunother 1997;20:60)
Essential features
  • Melanocyte lineage specific marker, more sensitive than HMB45 in the diagnosis of metastatic melanoma
  • Cytoplasmic protein
  • Positive in most primary melanomas but desmoplastic melanoma can be negative
  • Also positive in nonmelanocytic tumors with melanosomes, including angiomyolipoma, PEComa, lymphangioleiomyomatosis
  • Depending on antibody, positive in adrenal cortical tumors and sex cord stromal tumors
Pathophysiology
  • Melanosome specific protein
  • Plays a vital role in the expression, stability, trafficking and processing of Pmel17, which is critical to the formation of stage II melanosomes (J Biol Chem 2005;280:14006)
Interpretation
  • Cytoplasmic staining
  • Staining in any percentage of tumor cells is interpreted as positive
Uses by pathologists
Microscopic (histologic) images

Images hosted on PathOut server:

Contributed by Yao-Tseng Chen, M.D., Ph.D.

Lentiginous lesion, A103 vs. HMB45

Primary melanoma, A103 vs. HMB45

Metastatic melanoma, A103 vs. HMB45

Angiomyolipoma of the liver, A103



Contributed by
Semir Vranić, M.D., Ph.D.

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Small bowel, metastatic melanoma


Contributed by
Kristine Cornejo, M.D.

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Testis, Leydig cell tumor



Case of the Week #32:

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Kidney, atypical epithelioid angiomyolipoma



Case of the Week #109:

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Uterus, melanoma



Images hosted on other servers:
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Adrenal cortical adenoma, A103+

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Bladder PEComa, HMB45+, MelanA+

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Pancreas, PEComa (MelanA+)

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Skin, dermal nevus

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Skin, melanoma, fibrohistiocytic proliferation


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Skin, melanoma, sentinel lymph nodes with "stealth" metastases

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Skin, neurotized melanocytic nevi

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Small bowel, metastatic melanoma

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Stomach, metastatic melanoma, MelanA

Positive staining - normal
  • Melanocytes in skin, retina - both A103 and M2-7C10 clones
  • Adrenal cortex, testis (Leydig cells and occasional Sertoli cells), ovary (granulosa / theca cells, hilus and stromal cells) - clone A103 only
Negative staining - disease
  • All tumors not listed above, including all carcinomas, lymphomas, etc.
Board review question #1
Which of the following lesions will stain positively for MelanA antibody (clone A103) but does not express MelanA mRNA or protein?

  1. Adrenal cortical adenoma
  2. Angiomyolipoma
  3. Benign melanocytic nevus
  4. Lymphangiomyomatosis
  5. PEComa
Board review answer #1
A. Adrenal cortical adenoma. A103 stains adrenal cortical cells and steroid producing cells in testis and ovary due to antibody cross reactivity to an unknown molecule in these cells; these cells do not produce MelanA / MART1 mRNA or protein.
Board review question #2
Which of the following statements is false about gp100 (HMB45 antibody) and MelanA (A103 antibody)?

  1. Both are likely to be positive in angiomyolipoma
  2. Both are markers for melanocyte differentiation
  3. HMB45 is more sensitive than MelanA (A103) in detecting metastatic melanoma in sentinel lymph nodes
  4. Neither can be used to distinguish melanomas from benign nevi
  5. Only MelanA (A103 antibody) is positive in adrenal cortical adenoma
Board review answer #2
C. HMB45 is more sensitive than MelanA (A103) in detecting metastatic melanoma in sentinel lymph nodes is false. MelanA (A103) is more sensitive than HMB45 (gp100) in detecting metastatic melanoma in sentinel lymph nodes.