Original contributionKBA.62: a useful marker for primary and metastatic melanomas
Introduction
Melanoma diagnosis can be challenging, particularly in metastatic conditions, because it can mimic undifferentiated carcinoma, sarcoma, or large cell lymphoma. Furthermore, desmoplastic or spindle cell melanoma may be difficult to identify when tumor cells lack melanin pigment, when the biopsy is small, or in metastatic conditions. Moreover, these tumors sometimes display focal, equivocal staining or even negative staining for S-100 protein [1], [2], [3]. HMB-45 and Melan-A antibodies are of limited value in these cases because several studies have reported either very focal staining or virtually no staining at all with these 2 antibodies [4]. These discrepancies in sensitivity and specificity of melanoma markers have been confirmed by numerous studies on the best panel for the evaluation of sentinel lymph node (SLN) from patients with melanoma [5], [6], [7], [8], [9]. The strategy to enhance tumor detection consists of serial sections of lymph node. Several studies have shown that exhaustive sectioning permits a histologic review of the entire lymph node but does not increase significantly tumor detection [5], [10]. Although it is now recognized that immunohistochemistry is more sensitive than hematoxylin and eosin (H&E), there is no consensus regarding the optimal panel of antibodies [6], [7], [9], [11]. However, anti–S-100 protein antibody remains the gold standard and HMB-45 antibody the most commonly associated marker [12].
In 1995, we described a novel antimelanoma monoclonal antibody, designated KBA.62, which reacts with most of benign and malignant melanocytic proliferations and with well-differentiated squamous carcinomas [13]. However, the differential diagnosis between melanocytic proliferation and well-differentiated squamous carcinomas is not considered a challenging problem, easily resolved through morphological features and S-100/cytokeratin immunophenotype. Besides, other markers such as anti–S-100 protein, HMB-45, MITF, PNL2, and Melan-A antibodies known to react with nonmelanocytic tumors are nevertheless considered good melanoma markers [14], [15], [16], [17]. However, review of the literature showed that only a few studies have reported on KBA.62 antibody [1], [18], [19].
The purpose of the current study was to report our experience in the diagnosis of melanoma using KBA.62 by comparison with anti–S-100 protein and HMB-45 antibodies in both primary and metastatic conditions, including pure and combined desmoplastic melanomas, and with regard to the management of a series of 215 SLN biopsies.
Section snippets
Primary and metastatic melanomas
Cases diagnosed in 2005 were selected from the archives of the Department of Pathology, Centre Hospitalo-Universitaire (CHU) Purpan, Toulouse, France. The study was carried out in accordance with the institutional review board–approved protocol. Seventy-four primary melanomas consisted of 31 superficial spreading melanomas, 9 acral lentiginous melanomas, 15 lentigo maligna melanomas, 2 nodular melanomas, 3 pure desmoplastic melanomas (defined by fusiform melanocytes dispersed in a prominent
Primary and metastatic melanomas (Fig. 1, Table 1)
The results of KBA.62, HMB-45, and anti–S-100 protein stainings on primary and metastatic melanomas are detailed in Table 1. As expected, virtually all tumors were positive for S-100 protein. Overall, KBA.62 was positive in most cases (90/97 cases, 93%), with a moderate to strong membrane staining (Fig. 1B and E). The reactivities of KBA.62 and HMB-45 were comparable (93% versus 85.5%; P = .10), except for the 3 cases of pure desmoplastic primary melanomas and the nodal desmoplastic metastatic
Discussion
We have already reported the potential diagnostic value of KBA.62 monoclonal antibody in melanocytic neoplasms [13]. This antibody reacts with a not yet identified antigen, which can be detected on routinely fixed, paraffin-embedded tissues. However, during the past decade, only a few studies have dealt with this melanoma marker [1], [18], [19]. Interestingly, Kaufmann et al [18] compared tyrosinase, melan-A, and KBA.62 reactivity for the diagnosis of metastatic amelanotic melanomas. They
Acknowledgments
The authors acknowledge Florence Capilla, Michel March, and Jeanine Boyes for their excellent technical assistance.
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