HMB45

HMB‑45 is a monoclonal antibody that targets gp100, a pre-melanosome protein expressed in immature and activated melanocytes. In IHC, it shows cytoplasmic staining and is widely used to evaluate melanocytic lesions, particularly for assessing maturation in primary melanocytic tumours. Although valuable in diagnosing melanoma, it is not used as a standalone screening marker and is typically interpreted alongside other melanocytic markers. HMB‑45 can also be positive in certain non‑melanocytic tumours such as angiomyolipoma, PEComa, lymphangioleiomyomatosis, and TFE/TFEB‑rearranged renal cell carcinomas due to MiT‑family transcription factor driven by gp100 expression (1).

Recommended Controls

Criteria for acceptable staining is a cytoplasmic staining pattern. Recommended control to include a known malignant melanoma (high expressor), normal lung (negative control) and or a section of normal skin (normal dermal melanocytes will stain positive). HMB45 demonstrates a cytoplasmic pattern. Melanoma positive control and the lung as a negative control. Kidney is also recommended to be used as a negative control.

Expected staining pattern

Malignant melanoma (DAB Detection kit)

Normal Skin (DAB detection kit)

Malignant melanoma (ALK Phos detection kit)

Normal Skin (ALK Phos detection kit)

Disclaimer

These methods are intended as a guide only. Laboratories that wish to implement these methods should perform internal validation/verification prior to use. The RCPAQAP does not make any claim or warranty for the accuracy or performance of these methods.