Immunoperoxidase technique modified by counterstain with azure B as a diagnostic aid in evaluating heavily pigmented melanocytic neoplasms

Abstract

Heavily-pigmented melanocytic neoplasms are difficult to evaluate on routine hematoxylin and eosin stained slides because pigmented melanocytes are difficult to distinguish from the numerous melanophages that are usually seen in the background of these lesions. Immunoperoxidase staining for S100 protein or HMB-45 antibody using diaminobenzidine (DAB) as chromogen, which forms a brown product, does not adequately distinguish melanocytes from melanophages. We modified this technique by replacing hematoxylin as the counterstain with azure B, which stains melanin green-blue. Thus, positive melanocytes appear brown while melanin granules in their cytoplasm are green-blue. However, negative melanophages only stain green-blue. This technique is useful in evaluating heavily pigmented melanocytic lesions such as malignant melanomas, melanosis of regressing malignant melanoma, residual malignant melanoma in areas of granulation tissue with melanophages, blue nevi, pigmented spindle cell variant of Spitz's nevi and combined nevi.

Immunohistochemical Expression of Melanocytic Antigen PNL2, Melan A, S100, and PGP 9.5 in Equine Melanocytic Neoplasms

“…10 Melan A is one of the most commonly used melanocytic differentiation markers for human and canine melanomas. 6,14,24 In this study, Melan A was not expressed in any of the equine melanocytic tumors or in normal melanocytes of equine skin, although expression of Melan A has been reported in an equine melanocytic tumor and in equine melanocytic cell cultures. 3,25 Immunoreactivity of Melan A was not evaluated in nonmelanocytic equine tumors in those studies.…”

Targeting ER stress–induced autophagy overcomes BRAF inhibitor resistance in melanoma

“…To determine the role of autophagy in BRAFi resistance, we assessed autophagy induction in 6 BRAF V600E melanoma cell lines, including a set of paired cell lines that were BRAFi-sensitive, but had acquired BRAFi resistance through chronic in vitro exposure (15). We categorized cell lines as either BRAFi-sensitive (A375P, SKMEL5, MEL1617) or BRAFi-resistant (MEL1617R, WM983BR, MEL624) by treating cells with the highly specific BRAF inhibitor PLX4720 and identifying the IC 50 . Based on previous literature for BRAFi resistance mechanisms (15,16), we classified cell lines with nanomolar IC 50 s as BRAFi-sensitive and those with micromolar or millimolar IC 50 s as BRAFi-resistant (Figure 2A).…”

Spitz nevi and atypical Spitz nevi/tumors: a histologic and immunohistochemical analysis

“…For fatty acid synthase staining, its expression in sebaceous glands and stratum granulosum of the epidermis was used as internal positive control, in accordance with the recent work of Uchiyama et al 25 The sections were lightly counterstained by the Giemsa method so that unstained nuclei were light blue in color and any melanin pigment appeared green. 26 Each case was scored separately by two of the authors in a blinded fashion (PK and MPH). The cases, for which there was disagreement, were rescored jointly for consensus.…”