Background
Primary lung cancer, with its morbidity and mortality, occupies the first place among malignant tumors worldwide [
1]. Relevant study has shown that the 5-year survival rate of stage I and Stage IV lung cancer patients has a huge difference, which is 55.5% and 5.3% respectively [
2]. Therefore, the early diagnosis of lung cancer is very important. Currently, Lung CT examination is the main method to detect lung cancer [
3]. Since 2005, China has carried out a series of lung cancer screening programs based on lung CT examination, which has made great progress in the early diagnosis of lung cancer [
4‐
5], but the proportion of stage III-IV is still as high as 64.6% in the overall lung cancer [
6].
A number of recent international studies have shown that lung CT examination significantly improves the early detection rate of peripheral lung adenocarcinoma [
7‐
10], and more and more nodules with a diameter of less than 5 mm have been found early. However, in the clinical work, a large number of advanced central lung squamous cell carcinoma are still detected through bronchoscopy. Meanwhile, a part of CT-occult central lung squamous cell carcinoma and squamous epithelial precancerous lesions are also accidentally detected through bronchoscopy.
This study reviews the medical records of patients with primary lung cancer who are first diagnosed in the Bronchoscopy room of the Endoscopy Department of Zhejiang Cancer Hospital from January 2014 to December 2018, in order to evaluate whether the current lung CT examination mode is insufficient in the early detection of central lung squamous cell carcinoma and squamous epithelial precancerous lesions and determine which group of people need to undergo further bronchoscopy after lung CT examination.
Discussion
To our knowledge, this is the first study to evaluate the insufficiency of lung CT alone in the diagnosis of central lung squamous cell carcinoma and squamous epithelial precancerous lesions based on actual data from lung cancer patients. In this study, 130 cases of CT-occult lesions are found, and the data indicate that CT examination is insufficient in early detection of central airway lesions. Meanwhile, the data of this study show that operable peripheral adenocarcinoma is significantly better than single central squamous cell carcinoma in terms of postoperative tumor diameter and lymph node metastasis. These results indicate that compared with peripheral adenocarcinoma, the current lung CT examination has some insufficiency in the early diagnosis of central squamous cell carcinoma.
The increase in the number of lung cancer diagnoses between 2014 and 2018 is due to an increase in the detection of peripheral lung adenocarcinoma in this study. The number of squamous cell carcinoma diagnoses remains relatively stable. These data show that current lung CT examination has a significant advantage in the early diagnosis of peripheral lung adenocarcinoma (Table
1). Relevant international study shows that compared with non-lung CT screening group, adenocarcinoma accounts for the highest proportion of lung cancers detected through screening in the lung CT screening group [
12]. Meanwhile, relevant study also shows that the incidence of female lung cancer is increasing year by year [
13].
However, central squamous cell carcinoma is closely related to smoking. There are a large number of smokers in China, and central squamous cell carcinoma is still very common. Related study has shown that the common pathological subtypes are adenocarcinoma (74.58%) and squamous cell carcinoma (18.01%) in China. Adenocarcinoma (58.5%) and squamous cell carcinoma (31.6%) are the main pathological types in male patients, while adenocarcinoma (91.6%) and squamous cell carcinoma (3.4%) are the main pathological types in female patients. Adenocarcinoma and squamous cell carcinoma account for 50.6% and 37.7% respectively in smoking patients, the proportion of adenocarcinoma decreases with age, while squamous cell carcinoma and small cell carcinoma increases [
14]. Data from another study shows that as one of the most common histologic subtypes of Lung cancer, the overall prevalence of lung squamous cell carcinoma is reported to be approximately 30% [
15]. The overall international statistics show that in 2020, there were an estimated 2,206,771 new cases of lung cancer, with 1,435,943 in males and 770,828 in females worldwide. In males, 560,108 (39%) of all lung cancer cases were adenocarcinoma, 351,807 (25%) were squamous cell carcinoma. Most squamous cell carcinoma cases were found in the USA, China, and the UK [
16]. Therefore, early diagnosis of squamous cell carcinoma is still of great significance in China.
This study results indicate that compared with peripheral adenocarcinoma, the current lung CT examination has some insufficiency in the early diagnosis of central squamous cell carcinoma(Fig.
2; Table
3). Meanwhile, only 604 of central lung squamous cell carcinoma can be treated with surgery, and even if surgery is performed, patients will lose at least 20% of lung function, which directly affects the quality of life of patients. Related research also shows that lung squamous cell carcinoma accounts for about 20-30% of non-small cell lung cancer. When diagnosed, patients are often older, stage is late, complications are more frequent, and tumors are mostly located in the center, which is difficult to treat. The median survival of patients is about 30% shorter than that of patients with other non-small cell lung subtypes [
17]. Related research also shows that although lung squamous cell carcinoma accounts for only 15% of the lung cancer cases, more than 315,000 new cases are diagnosed each year.Squamous cell carcinoma has a poor prognosis with a five-year survival rate of less than 20% for patients with inoperable squamous cell carcinoma and limited treatment options [
18]. Only by realizing early diagnosis of central lung squamous cell carcinoma and squamous cell epithelial precancerous lesions can timely and reasonable treatment be carried out. Meanwhile, if the squamous epithelial precancerous lesions can be treated by minimally invasive treatment technique under bronchoscopy before they progress into squamous cell carcinoma [
19‐
20], the prognosis of patients will be further improved [
21‐
22].
CT-occult central lung lesions is reported in the literature as early as 1998, and its early diagnosis is still puzzling clinical workers today [
23]. Related study has shown that the occurrence of squamous cell carcinoma is a group of continuous changes from squamous cell epithelial dysplasia, from mild dysplasia to invasive carcinoma takes about 6 years [
24], and more than 50% of in-situ cancers can be transformed into invasive carcinoma within 30 months [
25]. Such pathological evolution makes early diagnosis of central squamous cell carcinoma possible. Since 2005, China has continuously carried out a number of lung cancer screening programs based on lung CT examination. Most of the patients in this study, especially the high-risk groups with a history of heavy smoking, have received at least one lung CT examination for various causes or lung cancer screening programs in the past 5 years. In this study, it is suggested that most mucosal epithelial lesions in the central airway are underdiagnosed due to CT-occult, and such lesions are not diagnosed for the first time until they results in respiratory tract related symptoms and could be detected by CT examination. This is the main reason for the large diameter and late stage of central lung squamous cell carcinoma at diagnosis. This reflects the insufficiency of CT examination in the early diagnosis of central lung squamous cell carcinoma and squamous epithelial precancerous lesions.
CT is the main means of lung cancer detection, in order to realize the early diagnosis of central airway disease, researchers in various countries have conducted a number of studies on CT. At present, 3D-CT can only achieve the localization and navigation of visible tumors in the lungs, and can not achieve effective diagnosis of early mucosal epithelial lesions in the central airway [
26‐
28]. In recent years, studies based on CT radiomics have been widely carried out. This research team has also used this technology to process CT images to predict the occurrence of CT-occult lesions in central airway, but the effect is still not satisfactory [
29]. At present, the early diagnosis of CT-occult lesions can only rely on bronchoscopy, related study has shown that bronchoscopy with autofluorescence and fluoroscopy detects precancerous bronchial lesions located at the level of the bronchial tree [
30]. Related research also shows that vascular patterns as visualized by narrow-band imagine also demonstrate acertain predictive role for the histological types of central lung cancer. It also has a high diagnostic value for early in situ squamous cell carcinoma [
31].
130 patients with CT-occult lesions and 583 (583/604,96.52%) patients with central lung squamous cell carcinoma undergoing surgical treatment are middle-aged and elderly men with a history of heavy smoking. Meanwhile, such data is in line with the age requirements of many international lung cancer screening programs, and people aged 55–75 are the key population for lung cancer screening [
32]. Therefore, for middle-aged and elderly men with heavy smoking, further bronchoscopy is very necessary when no abnormal findings are found in the central airway examined by lung CT.
The study still has some limitations, firstly, the study is a single-center study, and secondly, the patient data is from 2014 to 2018. Despite these limitations in this study, Zhejiang Cancer Hospital, as a regional cancer medical center, has a fixed source of patients, and the lung cancer screening based on lung CT examination has not changed since 2014, meanwhile, Zhejiang Province is a province with good economy, and the coverage of lung cancer screening is wide.so the data selected by this study is of certain research value.
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