To our knowledge, this is the first study to report on COVID-19 patients with a history of cancer in Japan. The factors associated with mortality were similar to those reported in previous studies conducted on general patients with COVID-19, including lymphocytopenia on admission. Patients who received myelosuppressive chemotherapy recently or received lymphocyte-reducing chemotherapy, such as BR, were found to have a greater risk of mortality and prolonged viral shedding periods.
Lymphocytopenia is one of the frequently mentioned features of COVID-19 and correlates with clinical severity [15,16,17]. In the same way, T-cell count in peripheral blood is also significantly reduced and associated with high mortality rate [18,19,20,21]. Moreover, T-cells from COVID-19 patients have significantly higher expression levels of PD-1 and Tim-3, which suggests the surviving T-cell appear functionally exhausted [19]. These results imply that cellular immune response necessary for effective viral elimination is attenuated in COVID-19 patients. In our study, the detectable SARS-CoV-2 RNA persisted for a median of 22 days from the illness onset in survivors, which is almost the same as that reported in previous studies in general patients [22, 23]. Interestingly, the virus was detectable for especially long duration in two patients who received BR, one of whom eventually died. This treatment is known to suppress cellular immunity and reduce lymphocyte count strongly compared with rituximab plus CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisolone) [24, 25]. Thus, BR makes cellular immune response much weaker, thus leading to the prolongation of viral shedding and poor outcomes. Likewise, highly myelosuppressive chemotherapy for hematological malignancy causes pancytopenia, and also lymphocytopenia as a matter of course, and can lead to severe COVID-19. Our finding showed that patients with low lymphocyte count had poor OS regardless of the presence or absence of recent cytotoxic agent administration (Fig. 1c). However, recent cytotoxic chemotherapy may be an important adverse factor in COVID-19 patients as a cause of lymphocytopenia.
Some retrospective study did not show any significant association between recent cancer treatment and mortality, as with our study [9,10,11,12]. However, one retrospective study in China reported a higher likelihood of experiencing severe events in patients who received antitumor treatment within 14 days of COVID-19 diagnosis [5]. We described the details of the outcome including the viral shedding period and its association with treatment in patients with active cancer (Fig. 2). In this study, two patients who received cytotoxic chemotherapy within the rest periods (azacytidine for AML and A + CHP for ALK-negative ALCL) developed severe COVID-19 and eventually died. On the contrary, patients with AML and ALL, who recovered from pancytopenia and remained in remission at the onset of COVID-19 after intensive treatment, were cured. Therefore, the risk of developing severe COVID-19 must be considered in patients who received myelosuppressive chemotherapy recently.
A recent study reported that patients with different tumor types have variable COVID-19-related mortality, with significantly increased case-fatality rate in patients with leukemia [26]. In this study, there was no statistically significant difference of OS between patients with hematologic and non-hematologic malignancy, which may be due to the limited number of study population. However, patients with hematologic cancer need very careful monitoring, because they are likely to receive intensive myelosuppressive chemotherapy and to develop severe COVID-19 as described above.
One of the important aggravating mechanisms of COVID-19 is cytokine release syndrome [27, 28]. Meanwhile, immune checkpoint inhibitors may also activate the immune system and cause cytokine release syndrome [29]. One retrospective study reported that immunotherapy within 90 days was an independent risk factor for hospitalization and severe disease in cancer patients [10]. In our study, two patients received immunotherapy within 30 days. One patient had elevated CRP and ferritin levels on admission and required high-flow nasal cannula oxygen therapy. However, they eventually recovered even without receiving glucocorticoids. Further study is needed to confirm the association between immunotherapy and mortality of COVID-19.
Coagulopathy is also one of the mechanisms that can exacerbate COVID-19. Patients with COVID-19 are at risk of thromboembolism, and an increase in the concentrations of circulating d-dimer indicates pulmonary vascular bed thrombosis with fibrinolysis [30]. Several studies reported that elevated d-dimer on admission predicted mortality [22, 31, 32]. Meanwhile, cancer patients are originally at high risk of venous thromboembolism [33, 34]. Although one retrospective cohort study in New York showed the association between d-dimer and mortality from COVID-19 in cancer patients [9], our study did not demonstrate a significant correlation between them. Determining the incidence of venous thrombosis in COVID-19 patients with cancer and interpreting the changes in d-dimer concentrations remain challenging.
This study has several limitations. First, this study was a retrospective, single center with a small sample size. Not all laboratory tests related to the prognosis of COVID-19, including albumin, serum ferritin, and d-dimer, were performed in all patients. We did not perform a multivariate analysis due to the lack of data and the small number of the study population. Second, we decided the cut off values of laboratory data by ROC curve. Although the best cut off values is unknown, the cut off value of lymphocyte count in this study, for example, is the same as the value used in the MuLBSTA score (< 0.8 × 109 /L), which predicts mortality risk in patients with viral pneumonia [35]. Additional studies based on larger cohorts are needed to define the most predictive cut off values for COVID-19. Third, the types of cancer and treatment were very heterogeneous in this study, because we included all patients who had a history of cancer. Although it was difficult to draw a conclusive evidence from such a study population, our study provided new insight on the clinical features of COVID-19 patients with cancer. Future studies with a larger sample size are needed to further explore the risk factors for mortality in COVID-19 patients according to cancer or treatment types.
In conclusion, our study suggested that the risk factors for mortality previously reported in general COVID-19 patients, including lymphocytopenia, were also effective in cancer patients. Awareness on the risk of chemotherapy that leads to severe cytopenia or suppresses cellular immunity during the COVID-19 pandemic must be improved.