Response to Letter to the Editor.

To the Editor:

We thank Dr. Seitlinger for the interest in our work and his comments. As Dr. Seitlinger mentioned in the letter, the diffusing capacity for carbon monoxide is a useful parameter to evaluate the diffusing capacity of the lung. In our center, spirometry and arterial blood gas test are routinely taken before operation for each patient; unfortunately, the diffusing capacity for carbon monoxide tests are not taken. The decision for operation was made on the basis of clinical performance, results of spirometry, and arterial blood gas test. In this cohort, patient 3 had a relatively poor lung function with forced expiratory volume in 1 second of 1.39 liter and percent forced expiratory volume in 1 second of 68.5%, whereas the preoperative arterial blood test on breathing air revealed a partial pressure of oxygen equal to 93 mm Hg and partial pressure of carbon dioxide equal to 34.1 mm Hg.

We also noted that the three patients in this cohort who died had comorbidities of interstitial lung disease, chronic obstructive pulmonary disease, and coronary atherosclerosis, respectively. As we know, comorbidities could raise the incidence of severe postoperative complications, which can further increase the risk of death for patients after lobectomy. In our cohort, none of the patients had surgery-related postoperative complications. Moreover, the clinical course of these seven patients illustrated that the disease worsened immediately after onset of symptoms of coronavirus disease 2019 (COVID-19) infection, and the fatality rate was much higher than that of the general population. These findings suggested that, besides comorbidities, the stress of lung resection might be a risk factor for death among patients who contracted COVID-19 during the perioperative period.

The effects of different operation patterns, including operation approach and lymphadenectomy on COVID-19, remains to be evaluated. Surgical stress results in a reduction in the number of CD8-positive T-cells that produce interferon gamma in response to tumor-associated antigen. Interferon gamma is an important cytokine involved in the antiviral immune response. Furthermore, operation induces an elevation in the number of circulating neutrophils followed by a strong elevation in the number of inflammatory monocytes. The systemic inflammatory response induced after surgical procedure promotes the emergence of tumors whose growth was otherwise restricted by a tumor-specific T-cell response. We speculated that surgical stress in patients with cancer might suppress the T-cell–mediated antiviral response.

It was indeed hard to draw a full picture on the basis of such a small sample size, but these cases provided important clinicopathologic information of the specific patient population at that time. We are thankful for the comments and for pointing out further research possibilities. Large studies and further investigation are necessary to evaluate the influence of operation on the progression of COVID-19.