Mixed nuclear-cytoplasmic immunostaining for cyclin D1, MMP-9, TIMP- 1 in actinic keratosis and correlation with cellular proliferation Hlushok VS 1 , Sviatenko TV 2 , Shponka IS 2 , Poslavska OV 2 . 1 Ternopil Regional Dermatovenerologic Dispensary, Ternopil, Ukraine 2 SE "Dnipropetrovsk Medical Academy", Dnipro, Ukraine Abstract. Actinic keratosis (AK) is an obligate precancerous skin condition that most often occurs in open areas of the skin (primarily, the head, neck and extremities) after prolonged or intense ultraviolet radiation exposure in genetically predisposed people. Materials and methods. Immunohistochemical study of vascularization and stromal degradation processes in 24 panch skin biopsy specimens (15 actinic keratoses and 9 seborrheic keratoses) with cyclin D1, MMP-9, TIMP-1, Кі-67 markers (Thermo Scientific, USA) was performed. The aim of the study was to analyze the expression of the cyclin D1, MMP-9, TIMP-1 and the cellular proliferation level of various clinical and morphological forms and stages of actinic keratosis severity , in comparison with seborrheic keratosis, for the development of effective differential diagnostic criteria. Results. Thus, by analyzing the immunohistochemical profile of samples of actinic keratosis, the following features can be separated: AK very often have the moderate mixed nuclear-cytoplasmic overexpression of cyclin D1 (33.33% of cases had an expression above 30%). In addition, in AK, these changes usually spread to the epithelium of hair follicles and sebaceous glands. In assessing the proteolytic activity in the AK and SC samples with the MMP-9 expression and its TIMP-1 antagonist, only a relatively strong correlation relationship was detected with the MMP-9 expression (p 3 =0.002186, C = 0.721), but the presence of aberrant expression MMP-9 and TIMP-1 in both subgroups further indicate the presence of cellular atypia and serves as a reliable prognostic indicator of increasing proliferative activity. Key words: actinic keratosis, seborrheic keratosis, cyclin D1, MMP-9, TIMP- 1, proliferative activity.