Several aspects related to the management of patients with cancer have been affected by the COVID-19 outbreak. The present study was conducted to examine the volume of surgical procedures and perioperative factors, including stage and histology, for lung cancer and mediastinal tumor cases during the long-term COVID-19 pandemic in Japan. According to the NCD, the number of surgeries for lung cancer and mediastinal tumors decreased in 2020 and did not recover until 2022. A possible main reason is the decrease in the number of diagnostic procedures conducted for thoracic malignancy due to fewer patients undergoing cancer screening and postponed diagnostic evaluations during the early pandemic period [5, 15]. It is also conceivable that a large number of individuals avoided undergoing regular medical checkups because of the pandemic situation, even in 2021 and 2022. There were widespread concerns regarding the increased risk of infection when visiting a medical facility or hospital, as well as regarding the increased burden on healthcare workers, even after the introduction of vaccines and other effective therapies for treating COVID-19.

The hospital-based cancer registry (HBCR) data presented by the National Cancer Center for Japan showed that the number of lung cancer patients steadily increased from 2014 to 2019 and decreased in 2020, remaining broadly flat (Fig. 5A). HBCRs are used in cancer care hospitals designated by the Ministry of Health, Labour, and Welfare as a condition of designation, and the data therein are estimated to represent approximately 80% of incident cases in Japan, including surgical and non-surgical patients [16]. While the exact numbers for all such Japanese cases may not be fully presented, there was no marked increase in the data. Currently, there is an ongoing increase in the number of older individuals in Japan (≥ 65 years old) that is forecasted to peak by 2042 [17]. Thus, since the incidence rate of lung cancer is age dependent, it is expected that the number of lung cancer cases will also increase. It is therefore possible that the number of patients with undiagnosed lung cancer will sharply increase in the near future.

A Trend in numbers of patients with primary lung cancer from 2014 to 2022 calculated from data published in the Annual Report of Hospital-Based Cancer Registries. B Trends in the clinical stage of lung cancer from 2019 to 2022. C Trends in the rate of surgical cases according to clinical stage of lung cancer from 2019 to 2022

Regarding mediastinal tumors, precise numbers related to the incidence of each mediastinal disease during the COVID-19 pandemic have not been presented because of rarity, and the present report is the first to describe the number of surgeries for mediastinal tumors, including thymic malignancy. It is not uncommon for a mediastinal tumor mass to be asymptomatic in the long term, with diagnoses following incidental findings frequently noted [18], underscoring the importance of medical checkups for early detection. Similar to lung cancer, the estimated rate of decrease in the number of surgical procedures for mediastinal tumors during the pandemic was 15%; thus, it is possible that, in the near future, the number of patients with previously undiagnosed mediastinal tumors will also increase.

Reyes et al. reported that 38% fewer new lung cancer cases were diagnosed compared to prior to the COVID-19 pandemic period, while there were more cases of symptomatic and severe lung cancer [19]. Furthermore, undiagnosed thoracic malignant diseases are anticipated to be revealed at a more advanced stage, resulting in an increased number of cases with a worse prognosis. These factors are associated with a significant risk of delays in the diagnosis and/or access to treatment, which may result in suboptimal therapeutic care for cancer patients, consequently contributing to increased mortality. Thus, the present study was conducted to evaluate the trends in the stage distribution of lung cancer and primary diseases related to mediastinal tumors.

There was no significant change in the clinical or pathological stage of the surgical cases of lung cancer during the period examined in this study. Notably, there have been no reports regarding the number of surgeries for thoracic malignancies during the long-term COVID-19 pandemic, and the present study is the first to show the current situation in Japan. According to data from HBCRs, no annual shift in the clinical stage of lung cancer, including surgical and non-surgical cases, has occurred (Fig. 5B). Furthermore, the annual rate of surgical cases at each stage was nearly the same from 2019 to 2022, indicating that the choice of treatment did not change during the pandemic (Fig. 5C). Japan’s statutory health insurance system provides universal coverage for all residents. During the pandemic, healthcare services were well maintained for patients with lung cancer and those affected by coronavirus infection. In addition, because computed tomography (CT) screening, which has an excellent ability to detect early lung cancer, is performed more frequently in Japan than in other countries, there are a significant number of incidental lung cancer diagnoses [20]. Consequently, the impact of the coronavirus pandemic on medical conditions varied among countries, not only for patients receiving care but also among healthcare systems and other related factors. However, although the number of surgeries for thymoma did not change, those for thymic cancer increased throughout the study period, while those for cysts, which are apparently benign disease cases, decreased (Fig. 4A). These findings are likely due to the selection of surgical indications according to the preoperative diagnosis of mediastinal disease.

The number of surgical cases of lung cancer and mediastinal tumor in Q2 of 2020 was markedly lower than that during any other period, which is in correlation with the first declaration of the state of emergency in Japan, from April 7 to May 25 of that year. While the rate of pathological stage 0–IA1 lung cancer cases decreased in Q2 and then increased in Q3 of 2020, that of stage IA2–IB cases decreased in Q3 (Fig. 3C). Similarly, the rate of adenocarcinoma cases decreased while that of non-adenocarcinoma cases increased in Q2 (Fig. 3D), likely because non-adenocarcinoma cases are determined based on the detection of an invasive tumor, which is more frequently noted in chest X-ray findings than in adenocarcinoma. Small peripheral lung adenocarcinomas with ground-glass nodules have been reported to be difficult or even impossible to detect using routine chest radiography [21]. Due to the pandemic, many diagnostic procedures, including chest CT and biopsy examinations, have been delayed [22]. Another possibility is that surgery for patients with early-stage adenocarcinomas was often postponed because of the first declaration of the state of emergency. Kato et al. reported that pathological outcomes of patients with stage I lung cancer during the early pandemic period tended to include larger tumors and invasive size due to surgery only being indicated for lung cancer with high malignancy [23]. Furthermore, Mayne et al. evaluated the impact of an extended delay to conduct surgery for stage I NSCLC and concluded that a delayed procedure was associated with a worse prognosis for stage IA2–IB adenocarcinoma and stage IB squamous cell carcinoma but not for stage IA1 adenocarcinoma or stage I squamous cell carcinoma [24]. The present findings also indicate that patients with early-stage lung cancer underwent surgery immediately after the state of emergency was declared, suggesting that delayed surgery for stage 0–IA1 lung cancer does not have an effect on the prognosis. The rate of surgical procedures for benign mediastinal tumor cases also decreased in Q2 of 2020, probably for the same reason as noted for lung cancer surgery.

There were no marked changes in the rates of postoperative pulmonary complications or 30-day mortality during the COVID-19 pandemic. Another study that used NCD data found that the mortality and morbidity rates in patients undergoing distal gastrectomy for gastric cancer were not worse during the pandemic than during the pre-pandemic period [25]. These results suggest that appropriate perioperative management is required for patients with cancer in Japan.

The decrease in VATS and increase in RATS procedures for lung cancer and mediastinal tumor cases might have reflected the spread of RATS following its approval as an insurable procedure by the National Health Insurance System in April 2018. Similarly, the increase in segmentectomy procedures for lung cancer may have been due to changes in surgical method selection based on the results of the Japan Clinical Oncology Group (JCOG) series (JCOG0802/WJOG4607L and JCOG1211), which showed that sublobar resection for small peripheral NSCLC could be considered an oncologically effective alternative to a lobectomy procedure [26, 27]. While the reasons for the increase in the number of open surgery procedures for lung cancer are unclear, reasonable speculation is possible, as patients with advanced lung cancer did not increase during the period. First, guidelines released by surgical societies early in the pandemic recommended open surgery over endoscopic surgery as a way of reducing the transmission of COVID-19 via surgical smoke [28]. Another possibility is that open surgery was favorably selected in consideration of surgical safety, and limits on the number of healthcare workers available during the pandemic may also have played a part.

Several limitations associated with the present study warrant mention. First, due to the retrospective nature and use of data obtained from the NCD, selection bias could not be avoided, and only short-term surgical data were evaluated. Although no increase in cases of advanced thoracic malignancy was found to be associated with the COVID-19 pandemic, the analyzed population included patients with a short-term follow-up period. Second, the study period was limited to 2019–2022. The legal classification of COVID-19 was downgraded to “Class 5” in Japan on May 8, 2023, placing it in the same category as common infectious diseases, such as seasonal influenza. Nevertheless, waves of increased COVID-19 infections were noted in 2022 and 2023, so it cannot be denied that the effects of the pandemic on surgery for thoracic malignant tumor cases will continue in the future. Additional studies are necessary to clarify the future effects of COVID-19 on trends in the stage distribution for lung cancer and primary disease in mediastinal tumor cases in Japan.

In conclusion, there were no marked changes in disease progression in thoracic malignancy cases that caused treatment delays during the prolonged COVID-19 pandemic in Japan. However, since the number of surgical procedures for lung cancer and mediastinal tumors decreased in 2020 and did not fully recover by 2022, there is a possibility that an increase in patients with these conditions may occur in the near future. Further research is required to better understand the long-term impact of the pandemic on the burden of care for related diseases.