Background: Immune suppression and coagulopathy development in cancer patients receiving chemotherapy determines a high incidence of complications, including venous thrombosis, and mortality from COVID-19 infection. There are still no explicit data on managing cancer patients when anticancer treatment is resumed after coronavirus disease. According to clinical guidelines for the prevention of venous thromboembolic complications in cancer patients receiving chemotherapy, patients with breast cancer are classified as having a low risk of these complications and do not require prophylactic anticoagulation. The purpose of this study was to assess the parameters of the blood coagulation system and the frequency of venous thrombosis in breast cancer patients with chemotherapy resumption after coronavirus disease. Methods: The study included 30 patients receiving anticancer medical therapy for breast cancer after COVID-19. Anticancer treatment was resumed no earlier than 4 weeks after clinical recovery, absence of SARS-CoV-2 RNAs in nasopharyngeal swabs, infiltrative lung damage according to a chest CT scan, exclusion of venous thrombosis by a lower extremity venous ultrasound. Control group included 20 breast cancer patients without a history of COVID-19. Stage I tumors were registered in 26.6% in the main group vs 15% controls; II - 40% vs 60%; III - 20% vs 15%. Some patients were diagnosed with distant metastases (stage IV- 13.3% vs 10%). Results: Initially, before chemotherapy resumption in the main group, half of the patients had elevated levels of fibrinogen and D-dimer compared with the control group (66.7% vs. 35%, p > 0.05). After a cycle of chemotherapy, a significant difference in the coagulation system parameters was noted (73.3% vs 30%). A lower extremity venous ultrasound after the end of the therapy cycle in the main group showed venous thrombosis in 3 patients (catheter-related n = 2, distal vein thrombosis of the lower extremities n = 1), while no venous thrombotic complications were detected in the control group (10% vs. 0%). Conclusions: Breast cancer patients after coronavirus disease 2019 have hemostasis abnormalities and higher risk of venous thrombosis, and the resumption of anticancer treatment increases the incidence of thrombotic complications. COVID-19 should be considered an additional risk factor of venous thrombosis in cancer patients and requires reconsideration of indications for prophylactic anticoagulation when resuming anticancer treatment for patients with breast cancer.