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Introduction. The incidence and mortality of malignant melanoma have increased steadily over the last decades; therefore, the development of novel diagnostic markers for malignant melanoma is of great importance. The purpose of the study was to assess whether the development of melanoma before any treatment is accompanied by the body changes and, in particular, DNA damage in the mononuclear cells of the peripheral blood of patients. Material and Methods. In 93 patients (26 men and 67 women) admitted to the N.N. Petrov National Medical Research Center of Oncology for surgical treatment of stage T1c-2a-b-3a-b4a-bN0-1 cutaneous malignant melanoma, and in 118 healthy people as a comparison group, the level of damage to DNA in peripheral blood mononuclear cells was studied using the “comet” method. All patients were divided into two groups: group 1 included 45 patients (13 men and 32 women) who were examined before a decision on treatment was made and group 2 consisted of 48 patients (13 men and 35 women) who previously underwent excision biopsy for melanoma. Results. The level of DNA damage in peripheral blood mononuclear cells, assessed by the comet assay, was found to be signifcantly higher in patients with melanoma than in the comparison group. Moreover, the increase in the level of DNA damage was similar both in patients with a primary tumor before starting any treatment and in those who previously underwent excision biopsy for melanoma. The relationship between the level of DNA damage in peripheral blood mononuclear cells and the morphological characteristics of the tumor cells was revealed. The Spearman correlation analysis showed that all parameters that determined DNA damage positively correlated with the thickness of melanoma according to the Breslow’s depth, and the percentage of DNA in the comet and the comet tail moment correlated with the stage of the disease. Conclusion. The development of cutaneous melanoma is accompanied by an increase in the level of DNA damage in peripheral blood mononuclear cells. The level of DNA damage in peripheral blood mononuclear cells refects the changes that occur in the patient’s body under the infuence of the tumor process, which may allow using this indicator as an additional criterion for the diagnosis and aggressiveness of melanoma.

P urpose of the study : to assess whether the determination of the grade of dNA damage in the blood lymphocytes of patients with metastatic melanoma can be a criterion for assessing the effectiveness of therapy. Material and Methods. The grade of dNA damage in blood mononuclear cells was studied using the comet assay in 10 patients with progressive metastatic melanoma before therapy with Nivolumab and 3–4 months after Nivolumab therapy. Results. It was revealed that prior to treatment the level of dNA damage in blood mononuclears was higher in patients with melanoma than in controls (healthy subjects). This level significantly decreased when stable disease or complete regression were reached, while it changed less significantly or increased in cases with disease progression. Сonclusion. The initial level and changes in lymphocyte dNA damage in patients with melanoma can serve as a criterion for assessing tumor response to immunotherapy with Nivolumab.