The Pathology Dictionary Team
February 17, 2023

What is HMB-45?

HMB-45 (Human Melanoma Black-45) is an antibody that binds to a protein called gp100. This protein is expressed in cells called melanocytes and tumours made up of melanocytes, including melanoma.

How is HMB-45 used in pathology?

HMB-45 staining is commonly used by pathologists to aid in the diagnosis and classification of tumors made up of melanocytes, including melanoma. In this context, it is used to distinguish melanoma from other types of cancer or noncancerous conditions that may look similar to melanoma under the microscope. However, it’s important to note that HMB-45 staining is not specific to melanoma and can also be found in other types of tumors, such as clear cell sarcoma and perivascular epithelioid cell tumors (PEComas). For that reason, HMB-45 staining should always be interpreted in the context of other diagnostic tests and clinical information.

How do pathologists test for HMB-45?

Pathologists perform a test called immunohistochemistry to look for cells that express HMB-45. The test is performed on a tissue sample such as a biopsy.

What does positive for HMB-45 mean?

Positive means that the cells in the tissue sample express HMB-45.

What does negative for HMB-45 mean?

Negative means that the cells in the tissue sample do not express HMB-45.

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