According to WHO, breast cancer is one of the most common forms of cancer in women. In 2020, 2.3 million women were diagnosed with breast cancer and 685,000 deaths from the disease were reported worldwide. This research aims to study the dynamics of the concentration of MMP8, osteopontin, and Ca2+ ions, as well as the pH level in patients with breast cancer during chemotherapy and specific dental treatment. Materials and methods. The study involved 60 patients, both men and women. All respondents were divided into groups by their oncological diseases: group 1 consisted of 20 patients with stage II and III breast cancer after chemotherapy, without prior dental treatment, group 2 comprised 20 patients with breast cancer after chemotherapy, with previous dental treatment, the control group included 20 people without cancer and dental pathology. Results and discussion. Dental diseases in patients of both groups were manifested by significant changes in bone metabolism, which was accompanied with sharp rise of MMP8 concentration in oral fluid during reducing osteopontin concentration. It is worth noting that the above pathobiochemical changes occurred against the background of a fall in the Ca2+ ion content and a pH shift towards the acidic side. The increase in Ca2+ is associated with a decrease in MMP8 level and the elevation in pH and osteoponine. In turn, the pH has medium power feedback with MMP8 and a direct relationship of medium force with osteoponin. MMP8 and osteopontin are associated with strong feedback, that is, an increase in the level of one of them can be displayed about reducing osteopontin. Conclusion. This study has established a statistically significant increase in MMP 8 against the background of the reducing concentration of osteoponitis. Pathobiochemical changes in bone tissue were found against the background of significant loss of Ca2+ ions and pH. Dental treatment for this category of patients has led to the improvement in the concentration of these markers. The data obtained justifies the necessity of their use as diagnostic markers and laboratory screening of the effectiveness of dental treatment in patients of this category.