Alternate Test Names:
gp100; Melanoma Specific Antigen; HMB45

Methodology: IHC

Clinical Significance:
Identifies: The gp100 protein, found in premelanosomes. As such, HMB-45 is a highly sensitive and specific marker of melanoma, particularly in the metastatic setting. The epitope targeted by HMB-45 behaves as an ‘oncofetal’ antigen that is not expressed in normal, resting melanocytes but is present in reactive and neoplastic melanocytic processes. Furthermore, as a marker of a premelanosomal protein, it is also an excellent marker of clear cell sarcoma as well as PEComas.

Subcellular Localization: Cytoplasmic, granular

Organ: Skin & Mucosa

Disease State: Clear Cell Sarcoma, Large Cell Undifferentiated Malignant Neoplams, Melanoma, PEComas, Spindle Cell Tumors / Sarcoma Subtyping

CPT Code(s): 88342 or 88341 (reference only; CPTs may vary)

Turnaround Time: Within 1-2 business days of receipt

Schedule: Monday - Friday

Specimen Requirements:
• Formalin-fixed, paraffin-embedded (FFPE) tissue block or cell block - OR -
• 1 unstained slide for each test requested plus 3-4 additional unstained slides cut at 4µm