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Soo Park, MD
Soo Park, MD
Posted: Wednesday, October 30, 2024
Immunohistochemically detected BCL6 corepressor (BCOR) overexpression was previously established as a marker of BCOR-altered round cell sarcoma, according to Chantal Pauli, MD, of University Hospital Zurich, and colleagues. Their findings from the present analysis, which were published in the journal Diagnostic Pathology, demonstrated the potential for strong aberrant positivity in Merkel cell carcinoma and other neuroendocrine neoplasms.
“Without considering the proper context and other immunohistochemical stains, this could potentially result in misinterpreting Merkel cell carcinoma as a sarcoma and lead to costly reflex testing for the detection of a BCOR genetic alteration,” the investigators remarked. “This pitfall might be particularly relevant in cases of Merkel cell carcinoma or small cell lung cancer [that] only exhibit a patchy cytokeratin expression, [which] potentially obscures their epithelial nature.”
The investigators presented three index cases of Merkel cell carcinoma that were found to clinically and radiologically mimic a sarcoma. Histologic analyses of biopsies from these patients revealed solid sheets of a small round blue cell neoplasm. Immunohistochemistry with a broad panel of antibodies was used for lineage classification. According to the investigators, positivity for synaptophysin, CK20, and Merkel cell polyomavirus large T antigen led to the diagnosis of Merkel cell carcinoma. They further noted strong positive nuclear staining for BCOR in all cases.
In a retrospective analysis of 31 tumor samples from 21 patients with Merkel cell carcinoma, 90% of cases exhibited at least focal positivity for BCOR (nuclear and/or cytoplasmic, strong: n = 2; heterogeneous moderate: n = 17; weak: n = 9). The expression was assessed against that of five BCOR-altered neoplasms as a positive control. Furthermore, the investigators examined 19 biopsy specimens from patients with small cell lung cancer; they found moderate (n = 8) to strong (n = 11) BCOR positivity in all cases.
Disclosure: The study authors reported no conflicts of interest.
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