Expression of minichromosome maintenance proteins in Merkel cell carcinoma

Minichromosome maintenance (MCM) nuclear proteins have barely been employed in the diagnosis of skin malignancies. We aimed to assess whether MCM immunohistochemistry can be utilized to examine tumour proliferation in Merkel cell carcinoma (MCC).

In this pilot study, we studied skin specimens of eight patients with MCC. As a control, eight patients with cutaneous malignant melanoma (MM) were included. Immunohistochemistry was performed for MCM4, MCM6, MCM7, Ki-67, p53, and p21.

Protein expression of MCM4 (66.0 +/- 26.5% vs. 33.9 +/- 22.4%; P = 0.017), MCM6 (70.9 +/- 11.9 vs. 31.7 +/- 22.7; P = 0.0031), and MCM7 (76.5 +/- 16.4% vs. 34.9 +/- 25.5%; P = 0.0013) was significantly increased in tumour cells of MCC when compared to tumour cells of MM. Ki-67 immunoreactivity was also significantly higher in MCC than in MM (28.7 +/- 7.9 vs. 11.0 +/- 9.2; P = 0.0012). Immunolabelling of p53 (68.6 +/- 26.2 vs. 58.4 +/- 28.8; P = 0.46) and p21 (40.1 +/- 38.8 vs. 25.8 +/- 16.1; P = 0.35) was relatively high but not significantly increased in MCC when compared to MM.

Our preliminary data indicate that MCM immunohistochemistry may be a useful tool for the determination of tumour cell proliferation in MCC.