S‐100 protein and SOX10‐positive breast carcinoma mimicking metastatic melanoma

Abstract

We present a case detailing a 70-year-old female with a history of triple-negative breast carcinoma (TNBC) of the left breast and contralateral stage pT2a nodular melanoma of the right upper arm who underwent sentinel lymph node biopsy of the right axilla demonstrating a metastatic epithelioid tumor that was strongly positive for S-100 protein and SOX10. The tumor cells were negative for HMB-45 and Melan-A and positive for CK7 and other breast markers (GCDFP15, mammaglobin, and GATA3). While concerning for metastatic melanoma based on clinical history and initial immunohistochemistry, tumor morphology and subsequent immunohistochemistry was supportive of metastatic breast adenocarcinoma. This case demonstrates a rare but perilous diagnostic pitfall of triplenegative breast carcinomas that strongly and diffusely express S-100 protein and SOX10 mimicking melanoma.

Breast Metastasis From Cutaneous Melanoma: Beyond the Infiltrating Ductal Carcinoma

“…S100 is a very sensitive marker for melanoma and is usually diffusely positive, but it is also positive in approximately 40% of mammary carcinomas. Sox10 is also diffusely positive in most melanomas but is positive in approximately 10% of breast cancers, particularly basal-like carcinomas [ 13 ]. Melan-A and HMB45 are useful because they are more specific, but staining is sometimes focal and they are occasionally expressed by breast cancer [ 14 ].…”

Melanocyte colonization and pigmentation of breast carcinoma: A case report

“…18 Things may get even more complicated in the case of pigmented triple-negative breast cancers, as SOX10 also labels primary breast carcinomas, particularly those with the basal-like, triple-negative phenotype. [19][20][21] In this particular circumstance, it is imperative to meticulously evaluate suitable immunohistochemical stains. Cases of similar pigmented invasive breast carcinomas from the literature are summarized in Table 1.…”

“…Recently, a similar case was stained with dual‐labeling (PHH3 and Melan‐A) and showed negative PHH3 labeling for the melanocytes, which indicated that the melanocytes were not undergoing mitosis 18 . Things may get even more complicated in the case of pigmented triple‐negative breast cancers, as SOX10 also labels primary breast carcinomas, particularly those with the basal‐like, triple‐negative phenotype 19–21 . In this particular circumstance, it is imperative to meticulously evaluate suitable immunohistochemical stains.…”

Pigmented Epidermotropic Breast Carcinoma: A Diagnostic Pitfall Mimicking Melanoma A Case Report and Literature Review

“…In fact, SOX10 and S100 protein positive staining are recognised in up to 50% and 66%, respectively, of breast carcinomas, particularly in triple-negative breast carcinomas, assigning further potential hazard in a pigmented epidermotropic carcinoma. [18][19][20][21][22][23] Melanotic carcinoma of the breast is considered a rare morphological variant of invasive breast carcinoma, of no special type (IBC-NST). 24,25 It is characterised by the combination of a carcinoma component, positive for cytokeratins and negative for melanocytic markers, interspersed with a melanocytic component, negative for cytokeratins and positive for melanocytic markers.…”

“…In fact, SOX10 and S100 protein positive staining are recognised in up to 50% and 66%, respectively, of breast carcinomas, particularly in triple-negative breast carcinomas, assigning further potential hazard in a pigmented epidermotropic carcinoma. 18–23…”