In 2013, 23,254 new cases of lung cancer were registered nationwide at Korean Central Cancer Registry (KCCR). To investigate the detailed clinical characteristics, treatment information, and outcomes of Korean lung cancer patients, the Korean Association for Lung Cancer (KALC) and KCCR selected data using systematic sampling method for initial analysis. First, 12 national or regional cancer centers were selected according to the number of lung cancer patients. Subsequently, two additional hospitals were selected by the KCCR and five by the KALC. Each of the national or regional cancer centers and the two hospitals selected by the KCCR recruited 10-20 patients; the five hospitals selected by the KALC registered approximately 50 patients.

Data regarding age, sex, body mass index (BMI), smoking history, histopathologic type, symptoms, performance status (PS), Eastern Corporative Oncology Group score, clinical stage (according to the seventh edition of the TNM International Staging System), treatment modality, and survival status were collected according to a standardized protocol. Patients were followed up until October 2016. Survival data for all patients were obtained from medical records, telephone interviews, and/or the record of National Health Insurance of Korea. The study protocol was reviewed and approved by the Institutional Review Board at the National Cancer Center. Informed consent was waived due to the retrospective nature of the study.

Comparison of baseline characteristics between survivor and non-survivor was performed using a Mann-Whitney U test for continuous variables and a chi-square or Fisher exact test for categorical data. All p-values were two-tailed, with statistical significance set at p<0.05. Risk factors for mortality were analyzed using the Cox proportional hazards model, and Kaplan-Meier survival analysis was used to evaluate differences in survival rates. Statistical analyses were performed using SPSS version 20.0 for Windows (IBM Corp., Armonk, NY, USA).

A total of 489 lung cancer patients were enrolled at the 19 sites, the baseline characteristics of which are summarized in Table 1. The median patient age was 69 years (interquartile range, 60-74 years), 65.4% of patients were male, and 62.1% of patients were ever-smokers. Of the male patients, 88.6% were former or current smokers, while only 11.5% of the female patients had a history of smoking. Cough (33.5%) was the most common symptom at the time of diagnosis, and 13.1% of patients were asymptomatic. Among patients with NSCLC, proportions of asymptomatic patients in each clinical stage were 29.2% (in stage I), 20.5% (in stage II), 7.0% (in stage III), and 6.3% (in stage IV), respectively. PS score data were available from 351 patients, and 14.2% of patients showed poor PS (PS ≥2). The proportion of NSCLC patients at each clinical stage was as follows: stage I, 25.6%; stage II, 9.5%; stage III, 22.9%; and stage IV, 42.0%. According to the sex, the clinical stages of NSCLC patients were I (19.0%), II (9.0%), III (28.0%), and IV (44.0%) in male patients and I (28.8%), II (9.6%), III (10.3%), and IV (51.3%) in female patients, respectively. In small cell lung cancer (SCLC) patients, 36.8% were at a limited stage of disease and 52.6% were at an extensive stage. Among patients with adenocarcinoma, epidermal growth factor receptor (EGFR) mutations were found in 13.4% of patients and 31.7% of patients performed EGFR mutation test, respectively. A total 76.5% of patients were treated by surgery, chemotherapy, or radiation therapy.

During follow-up, there were 277 patient deaths (56.6%). The non-survival group was characterized by older age, a higher proportion of males, lower median BMI, and a higher proportion of ever-smokers when compared with the surviving group. In addition, the non-survival group had fewer asymptomatic patients, lower PS, and a higher incidence of metastatic disease than patients who survived the follow-up period. The surviving group had a higher proportion of patients who received treatment, particularly surgery.

In the overall population, the most frequent histological subtype was adenocarcinoma (48.7%), followed by squamous cell carcinoma (27.2%) and SCLC (11.5%). While squamous cell carcinoma (37.2%) was the leading subtype in male patients, adenocarcinoma showed the highest incidence in female patients, accounting for 76.3% of lung cancers (Figure 1).

In patients with NSCLC, 47.2% of patients underwent surgery, followed by chemotherapy (27.9%) and radiation therapy (23.7%), after initial diagnosis. By contrast, chemotherapy (69.8%) was the most common treatment modality in patients with SCLC and only four patients received surgery after the initial SCLC diagnosis (Table 2).

The median follow-up period was 504 days (interquartile range, 182-1,038 days). On univariate Cox analysis, age, male sex, lower BMI, smoking history, absence of symptoms, weight loss, poor PS, SCLC, metastatic disease, and no treatment were all significant predictors of mortality in patients with lung cancer. In multivariate Cox analysis, age, lower BMI, smoking history, absence of symptoms, SCLC, metastatic disease, and no treatment were seen to be meaningful predictors of mortality in total subjects (Table 3).

While treatment, age, and weight loss were significant prognostic factor in stage I-II NSCLC patients, meaningful prognostic factor in stage III-IV NSCLC patients were treatment status, age, sex, BMI, and PS. In addition, although proportion of asymptomatic patients in stage III-IV NSCLC was relatively low, absence of symptoms was significant prognostic factor in these patients (Supplementary Table S1).

When underweight patients (BMI <18.5) were evaluated in total patients, Kaplan-Meier survival analysis showed that the survival period of this sub-population was significantly shorter than that of the remaining patients (p<0.001) (Figure 2).