Minichromosome maintenance protein expression according to the grade of atypism in actinic keratosis.

The minichromosome maintenance (MCM) family is a group of proteins that are key initiation factors for DNA replication and are expressed only in cycling cells. Recent studies on various cancerous conditions have shown that MCM proteins are better markers for malignant cells compared to other proliferative markers. It has been also proven that MCM proteins are independent prognostic factors. The aim of this study was to characterize the pattern and frequency of MCM 2 protein expression in actinic keratosis (AK) and determine whether the expression is correlated with the degree of histological atypism. Biopsy samples of 34 patients who had been diagnosed as AK were used in this study. Samples were divided into three groups (grade I, grade II, and grade III) according to the degree of atypism. Immunohistochemical staining for MCM 2 protein, Ki-67, and proliferating cell nuclear antigen was performed, and the number of positively staining cells per unit area (10⁻⁴ μm²) was calculated for evaluation of immunoreactivity. MCM 2 protein was expressed in atypical keratinocytes in AK. Mean numbers of immunoreactive cells positive for MCM 2 were 165.1 in grade I, 304.5 in grade II, and 513.3 in grade III. Moreover, the correlation between the immunoreactivity for MCM 2 protein and AK grade was significantly more positive than that for other markers. Thus, we suggest that MCM 2 protein is a reliable marker for diagnosing and grading AK and further could be hypothesized as an important prognostic factor.