Subungual keratoacanthoma: analysis of cell proliferation and copy number variation of oncogenes compared with periungual squamous cell carcinoma

P>Background. Subungual keratoacanthoma (SUKA) is a rare cutaneous tumour with several features distinct from ordinary KA. SUKA may not show spontaneous regression and sometimes grows progressively, resulting in phalangeal bone destruction. This makes its distinction from digital squamous cell carcinoma (SCC) difficult. Aim. To investigate differences in molecular expression between SUKA and digital SCC. Methods. In addition to immunohistochemical analysis of Ki-67, one of the markers differentiating KA from SCC, we investigated the copy numbers of various oncogenes by multiplex ligation-dependent probe amplification (MLPA) using two cases of SUKA and three cases of periungual SCC. Results. Ki-67 was moderately or strongly positive in SCC but negative in SUKA. The MLPA analysis showed that the nuclear factor (NF)kappa B1 and cortactin (CTTN; formerly known as EMS1) genes are amplified in SUKA but not in digital SCC. This increase in NF kappa B1 was confirmed by immunohistochemical analysis. Conclusion. NF kappa B1 could be a novel marker to differentiate between SUKA and SCC. Although this study was performed on limited numbers of patients with SUKA, MLPA analysis could be applied to differentiate other benign tumours from their malignant counterparts.