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Karl D. Lewis, MD


Diagnostic Utility of Immunohistochemistry for Cutaneous Basaloid Neoplasms

By: Julia Fiederlein
Posted: Tuesday, May 24, 2022

According to David P. Frishberg, MD, of Cedars-Sinai Medical Center, Los Angeles, and colleagues, morphologic analysis alone may be insufficient to distinguish among cutaneous basaloid neoplasms. A retrospective analysis, which was published in Applied Immunohistochemistry & Molecular Morphology, evaluated the diagnostic utility of immunohistochemistry in this clinical context.

“Except Ki67, our immunohistochemical panel showed no significant added diagnostic utility of immunohistochemistry in discriminating among trichoepithelioma, desmoplastic trichoepithelioma, morpheaform basal cell carcinoma [MBCC], and microcystic adnexal carcinoma,” the investigators commented. “Among the four cutaneous neoplasms, desmoplastic trichoepithelioma and MBCC show a small but discernible difference in Ki67.”

The investigators identified patients with a final histopathologic diagnosis of trichoepithelioma (n = 14), desmoplastic trichoepithelioma (n = 9), MBCC (n = 6), and microcystic adnexal carcinoma (n = 6) from whom samples were collected and stained with nine immunohistochemical markers: p40, IMP3, ProEx C, p16, CK20, Ki67, androgen receptor, D2-40, and beta-catenin. Contrary to previous findings, CK20 and IMP3 were found to be negative in all cases. Androgen receptor immunoreactivity was observed in trichoepithelioma alone. Among the evaluated cutaneous basaloid neoplasms, the expression levels of beta-catenin, p16, ProEx C, and p40 did not seem to significantly differ.

The mean Ki67 labeling index was 8% for MBCC and 3% for desmoplastic trichoepithelioma. Of note, the proliferation index for trichoepithelioma (15%) appeared to be significantly higher than that of MBCC. A total of 100% and 36% of the microcystic adnexal carcinoma and trichoepithelioma cases, respectively, were found to express D2-40; on the other hand, neither the MBCC nor desmoplastic trichoepithelioma cases demonstrated D2-40 immunoreactivity. According to the investigators, in all cases of desmoplastic trichoepithelioma, the results confirmed the previously published observation of scattered CK20-positive Merkel cells in the epidermis; no Merkel cells were identified in the MBCC and microcystic adnexal carcinoma cases.

Disclosure: The study authors reported no conflicts of interest.

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