SOX10/Keratin Dual-Color Immunohistochemistry:
An Effective First-Line Test for the Workup
of Epithelioid Malignant Neoplasms in FNA
and Small Biopsy Specimens
Jeffrey K. Mito, MD, PhD; James R. Conner, MD, PhD; Jason L. Hornick, MD, PhD;
Edmund S. Cibas, MD
; and Xiaohua Qian, MD, PhD
BACKGROUND: The characterization of poorly differentiated neoplasms in fine-needle aspiration (FNA) and small biopsy
specimens usually requires immunohistochemistry (IHC) with a panel of markers. Because of an increasing need to pre-
serve limited diagnostic material for tumor genotyping and a mounting demand for cost containment, the authors investi-
gated the usefulness of dual-color IHC with antibodies directed against broad-spectrum keratins and SOX10, a
neuroectodermal transcription factor consistently expressed in melanoma, in the workup of epithelioid malignant
neoplasms. METHODS: A total of 107 cases of FNA cell blocks (49 cases) and small biopsies (58 cases) were selected,
including 34 melanomas, 31 epithelioid/pleomorphic sarcomas, and 42 carcinomas. IHC was performed on all specimens
using a peroxidase-based brown chromogen for SOX10 and an alkaline phosphatase-based red chromogen for keratins
AE1/AE3. The presence or absence of staining in lesional cells was scored. RESULTS: The majority of tumors demonstrated
1 of 3 distinct patterns: 1) malignant melanomas with nuclear SOX10 (sensitivity of 94% and specificity of 95%); 2) epithe-
lioid/pleomorphic sarcomas negative for both SOX10 and AE1/AE3 (sensitivity of 84% and specificity of 88%); and 3) car-
cinomas with cytoplasmic AE1/AE3 (sensitivity of 76% and specificity of 98%). In addition, a fourth pattern with
cytoplasmic AE1/AE3 and nuclear SOX10 was observed in a subset of carcinomas, most notably triple-negative breast
cancers. CONCLUSIONS: SOX10/keratin dual-color IHC appears to be an effective, sensitive, and specific test to distinguish
between melanoma, sarcoma, and carcinoma. This approach can identify melanoma, prioritize additional studies, and limit
the number of markers needed to workup an epithelioid malignant neoplasm, thereby potentially reducing costs and pre-
serving valuable tissue for ancillary studies with which to guide therapy. Cancer Cytopathol 2018;126:179-89.
American Cancer Society.
KEY WORDS: AE1/AE3; dual-color immunohistochemistry; epithelioid; fine-needle aspiration (FNA); melanoma; poorly dif-
ferentiated; sarcoma; SOX10; triple-negative breast carcinoma; unknown primary.
The timely and accurate diagnosis of poorly differentiated epithelioid neoplasms often is challenging due to a
broad differential diagnosis that includes melanoma, carcinoma, and certain sarcomas with an epithelioid mor-
phology. Thus, a panel of immunohistochemical stains covering several lineages of differentiation often is
required for the precise classification of these tumors.
This is especially true in the 3% to 5% of patients who
Corresponding author: Xiaohua Qian, MD, PhD, Department of Pathology, Brigham and Women’s Hospital, 75 Francis St, Amory 3, Boston, MA
Department of Pathology, Brigham and Women’s Hospital, and Harvard Medical School, Boston, Massachusetts
James R. Conner’s current address: Department of Pathology and Laboratory Medicine, Mt. Sinai Hospital, Toronto, Ontario, Canada
Presented in part at the 104th Annual Meeting of the United States and Canadian Academy of Pathology; March 21-27, 2015; Boston, MA.
Received: September 8, 2017; Revised: November 18, 2017; Accepted: December 1, 2017
Published online January 31, 2018 in Wiley Online Library (wileyonlinelibrary.com)
DOI: 10.1002/cncy.21960, wileyonlinelibrary.com