[1718] Expression of Melanoma Markers in Plasma Cell Dyscrasias (PCD): A Possibility for Misdiagnosis

MK Atieh, GA Barkan, EM Wojcik, S Alkan. Loyola University Medical Center, Maywood, IL

Background: Plasma cells have not been known to express melanocytic markers such as S100 and Melan-A/Mart-1. Due to a recent case of a plasmacytoma mimicking a melanoma (morphologically as well as immunohistochemically) in a patient with history of melanoma, we have pursued the current study to evaluate the potential ability of neoplastic plasma cells to express melanocytic markers.
Design: A retrospective database search was performed for PCD (plasmacytoma (P) or multiple myeloma (MM)) from 1998 to 2007. Only patients with a documented diagnosis of a PCD were included. A total of 37 cases were used in this study, (5-P, 32-MM). The patients ages ranged from 28 to 89 years (mean= 52.5 years) with 54% being male, and 46% female. Tissue microarray blocks were made from the paraffin embedded tissue using 4-mm cores. Slides from these tissue microarray blocks were stained with H&E, S100 and Melan-A/Mart-1. Staining intensity was graded as negative, 1+, 2+, and 3+ when compared to the control slides. Zero and 1+ staining were noted as negative, 2+ and 3+ staining were noted as positive.
Results: Analysis of the immunohistochemical stains in plasma cells showed that 5/37 cases (13.5 %) exhibited a diffuse staining pattern with strong cytoplasmic positivity for both S100 and Melan-A/Mart-1. Of these, 4/5 (80%) were from patients that had a diagnosis of multiple myeloma; 1/5 (20%) had a diagnosis of plasmacytoma.

Plasma Cell Expression Of Melanoma Antigens

	S100(n,%)	Melan-A/Mart-1(n,%)
NEGATIVE	32(86.5%)	32(86.5%)
1+	0(0%)	0(0%)
2+	3(8.1%)	1(2.7%)
3+	2(5.4%)	4(10.8%)

Conclusions: It can be difficult to render a diagnosis of a PCD in a patient with a history of malignant melanoma when complicated by atypical plasma cell morphology with expression of aberrant melanoma antigens. We have shown that 13.5% of PCD express S100 and Melan-A/Mart-1. If the suspicion for a PCD is high, other immunohistochemical stains (CD 138 and kappa/lambda light chain) and additional modalities should be utilized to rule out such a diagnosis. The current study aims to alert practicing pathologists to this potential pitfall that they may encounter in their daily practice.
Category: Techniques

Monday, March 9, 2009 9:30 AM

Poster Session I Stowell-Orbison/Autopsy Award # 243, Monday Morning