BAP-1 Expression Status by Immunohistochemistry in Cellular Blue Nevus and Blue Nevus–like Melanoma

Abstract

The family of blue nevi includes the common blue nevus (BN), cellular blue nevus (CBN), and atypical BN, while melanomas with BN-like morphology can either arise in association with a blue nevus (MABN) or in the de novo setting mimicking cellular blue nevus (MMCBN). Recent molecular and immunohistochemical studies have demonstrated loss of BAP-1 in MABN/MMCBN but not in BN/CBN, suggesting that loss of BAP-1 correlates with a malignant phenotype in these lesions. In this study, we applied anti–BAP-1 antibodies to a series of CBN/BN (n = 11) and MABN/MMCBN (n = 4). Nuclear BAP-1 expression was detected in the majority of CBN/BN (n = 10/11) but was lost in 1 case. Most cases of MABN/MMCBN showed loss of nuclear BAP-1 expression (n = 3/4), with one case of MMCBN showing preserved BAP-1 expression. Demonstration of BAP-1 loss in a single case of CBN and preservation of BAP-1 expression in 1 case of MMCBN may indicate that detection of alterations in BAP-1 protein expression by immunohistochemistry may not be a completely reliable biomarker for the distinction of BN/CBN from MABN/MMCBN. Further investigation of the significance of BAP-1 loss/preservation in BN-like tumors is warranted.

Melanocytic lesions with blue naevus‐like (dendritic) morphology: an update with an emphasis on histopathological, immunophenotypic, and molecular features

“…showed that 64% (7/11) of MBNs lacked immunohistochemical BAP‐1 nuclear expression, whereas none (0/24) of the CBNs in their cohort showed loss of immunohistochemical BAP‐1 nuclear expression. Similar results were also obtained in a recent study by Chen et al 32 …”

“…Furthermore, CBNs lack β‐catenin nuclear expression, 30 which is a useful immunophenotypic feature that helps to distinguish CBNs from one of their histological mimics, deep penetrating naevus (DPN) (see below for more details). BAP‐1 nuclear expression is almost always preserved in CBNs 31,32 . This contrasts with melanomas with BN‐like morphology (see below for more details), some of which can show loss of BAP‐1 nuclear expression 31,32 .…”

“…BAP‐1 nuclear expression is almost always preserved in CBNs 31,32 . This contrasts with melanomas with BN‐like morphology (see below for more details), some of which can show loss of BAP‐1 nuclear expression 31,32 . Currently, the frequency of PRAME expression and its diagnostic utility in CBNs is largely unknown.…”

Subcutaneous nodule showing loss of BAP1 in large plaque‐type blue nevus: Melanoma or not?

“…3 Recently, Costa et al 4 reported that loss of nuclear BAP1 expression strongly supported the diagnosis of melanomas associated with BN; however, a case of cellular BN with BAP1 loss was also reported. 5 In the present case, extremely unique features of both benign (low atypia and mitosis, and low MIB-1 reactivity) and malignancy (loss of BAP1 and abnormal FDG uptake) led to difficulty in diagnosis. Future studies investigating the accuracy of BAP1 staining and PET/CT to make a correct diagnosis of subcutaneous mass developed in PTBN with a large sample size are required.…”

“…Recently, Costa et al 4 . reported that loss of nuclear BAP1 expression strongly supported the diagnosis of melanomas associated with BN; however, a case of cellular BN with BAP1 loss was also reported 5 …”