DESCRIPTION

Dr. Jeyrroy Gabriel
Senior Specialist Biomedical Scientist | St. John’s Specialist Dermatology Laboratories at St Thomas' Hospital London

The diagnosis of heavily pigmented melanocytic lesions is problematic. This is often compounded by lack of visibility of nuclear detail of tumour cells due to physical masking by melanin pigment. Similarly there can be colour merging of chromogenic final reaction products with melanin, making evidence of antigenic localisation problematic. There is a number of melanin bleaching techniques available, the most widely employed method for immunohistochemical (IHC) assessments is the use of dilute hydrogen peroxide (H2O2). All methods to date have involved the bleaching of melanin as a manually performed primary step before loading subsequently bleached slides onto automated IHC platforms. Here we define a semi- automated bleaching procedure that allows full integration on one of the most widely employed automated IHC staining platforms. The bleaching protocol was defined on a widely used platform and involved the assessment of 24 histological cases of heavily pigmented malignant melanoma lesions (13 cutaneous and 11 metastatic) which were routinely fixed processed and paraffin wax embedded. Completion of the bleaching was assessed on H&E preparations performed following the semi-automated bleaching step for 60 minutes at 42 degree Celsius. Complete IHC staining was achieved on the IHC automated platform within 5 hours including the bleaching step. Results were consistent across all tissue evaluated. This data provides evidence that the dilute H2O2 bleaching procedure can be adapted for integration on one of the most widely employed automated IHC staining platforms and as a result improve the efficiency and reproducibility of the technique.

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