The COVID-19 pandemic has affected the entire global healthcare system. The rising incidence of COVID-19 and the shortage of medical resources and healthcare workers in hospitals have impacted the treatment of people with various chronic diseases such as cancer and other comorbidities, especially the elderly. During the COVID-19 pandemic, cancer patients face greater challenges as they have a higher risk of progression and severe infection and, ultimately, mortality. Not all types of solid cancer and hematological malignancies have the same impact on the prognosis of patients infected with the SARS-CoV-2 coronavirus. The available data are extremely contradictory; the mechanisms of multidirectional interactions are practically not studied. On the one hand, COVID-19 negatively affects cancer patients because they have a weakened immune system, and on the other hand, the immunosuppressive state inherent in cancer excludes the cytokine storm, which predetermines multiple organ failure and mortality in patients with COVID-19. Most experts have stated that the factor in the progression of COVID-19 to severe forms and death is not so much the malignant process itself, but antitumor cytotoxic chemotherapy during the last few months before infection with the SARS-CoV-2 coronavirus, which worsens the somatic status of patients, increases susceptibility and suppresses resistance to infections. Full vaccination against SARS-CoV-2 significantly reduces the risks and increases the survival rate of cancer patients with COVID-19, but mortality remains high. Therefore, this group of patients should always be the priority for all types of preventive protection.