Immunohistochemical Localization of Phosphorylated and Unphosphorylated Form of β-catenin With Regard to Shadow Cell and Squamous Differentiation in Cutaneous Pilomatricoma

Onychomatricoma: a clinicopathological, immunohistochemical, and molecular study of 10 cases highlighting recurrent RB1 deletion and the potential diagnostic value of LEF-1

AIMS

Onychomatricoma (OM), an uncommon benign fibroepithelial neoplasm of the nail unit, is sometimes diagnostically challenging for clinicians and pathologists. OM consistently expresses CD34, but no specific immunohistohemical markers or recurrent genetic alterations have been identified to date. Recent studies have suggested that Wnt signalling is a key molecular characteristic of OM.

METHODS AND RESULTS

Ten cases were analysed: four classical OM including two with pleomorphic cells; two superficial acral fibromyxoma-like variants of OM; three micropapilliferum variants of OM including one with pleomorphic cells; and one proliferating variant of OM. Immunohistochemically, the spindle cells were positive with CD34 (n = 10) and CD99 (n = 1), with focal reactivity for CD10 (n = 5). The epithelial component of the tumours expressed immunopositivity for LEF-1. Using array comparative genomic hybridization (aCGH), we demonstrated that all OM, including its variants that were tested (n = 8), harboured a few copy number alterations with losses of whole or part of chromosome 13 including the RB1 gene (n = 8) and chromosome 16 (n = 6).

CONCLUSION

We report a recurrent loss of RB1 (13q) as a possible driver molecular event in OM indicating a relationship between OM and other lesions of the spectrum of the so-called '13q/RB1' family of tumours. We did not identify a role for the Wnt/beta-catenin signalling pathway, as has been proposed in a recent study. LEF-1 could be a potential sensitive and specific marker of OM and should be used in the differential diagnosis between OM, superficial acral fibromyxoma, and the CD34-positive fibrosing family of tumours.

Novel Mutations in Pilomatrixoma, CTNNB1 p.s45F, and FGFR2 p.s252L: A Report of Three Cases Diagnosed by Fine-Needle Aspiration Biopsy, with Review of the Literature

Pilomatrixoma (calcifying epithelioma of Malherbe) is an uncommon benign skin appendageal tumor that differentiates toward hair matrix cells. It is misdiagnosed in up to 75% of cases by nondermatologists. Although the histopathological findings are well recognized and characteristic, diagnosis by fine-needle aspiration biopsy may be quite challenging. Several reports have emphasized the challenges in cytodiagnosis of pilomatrixoma, leading to a false-positive diagnosis. The lesions may show avidity for fludeoxyglucose on positron emission tomography/computed tomography scan, raising concern of a possible malignant neoplasm. CTNNB1 mutations have been reported in a high percentage of pilomatrixomas. Expression of β-catenin, the protein encoded by CTNNB1, is also frequently observed. To determine if routine cytological specimens can be successfully used to perform additional investigation and support or confirm the diagnosis in three cases of pilomatrixoma, we performed molecular analysis and immunohistochemistry to search for CTNNB1 mutation and β-catenin, respectively. β-Catenin positivity by immunohistochemistry was observed in basaloid cells in all three cases. Exon 3 mutations in CTNNB1 were detected in all cases. In addition, we detected a fibroblast growth factor receptor 2 (FGFR2) mutation in one of the cases. We reviewed the literature and present the clinical and morphological characteristics that must be considered along with other findings to accurately achieve the correct diagnosis, in correlation with the results of the ancillary technique. In conclusion, routine cytological specimens can be successfully used to perform additional investigations and support cytodiagnosis in difficult cases.