Interpretation of Common Used Tumor Markers Affected by Systemic and Inflammatory Diseases Introduction: An examination of tumor markers is often made as a basis for the successful diagnosis and follow-up treatment of patients with malignant tumors. However, are tumor markers truly significant by themselves, or are they just a baseline quantitative expression of value that we use to diagnose a patient as better or worse based on it increasing or decreasing value? Objective: This paper attempts to answer the question of what factors can affect serum protein and mucin markers and thus lead to a misinterpretation of their results. Methods: Tumor markers were determined by isotopic and non-isotopic laboratory analysis methods, using operational protocols of the immunoanalytic laboratory. All methods were checked using internal quality control, and four times a year using an external quality control. Additionally, 16 236 samples were analysed using 3180 probands during the period 2008-2014. Results: We discovered that in premenopausal women, the markers AFP, CA 125 and HE 4 rise during ovulation peak periods while other markers changed minimally or not at all. However, in postmenopausal women, we proved the incidence of a false positivity marker. With women in the 1st and 2nd trimester of pregnancy, the...