SCLC Patients in SEER Database

Because the PI status has been recorded since 2010 based on the term, cs site-specific factor 2, patients were identified from the SEER database between 2010 and 2018. The inclusion criteria were as follows: (a) malignant tumor located in the main bronchus and lung (Site code: C340-C349); (b) patients diagnosed with primary SCLC (Histology code: 8002, 8041, 8042, 8043, 8044, 8045); (c) diagnostic confirmation based on positive histology or positive microscopic confirmation; (d) the status of PI was recorded clearly; (e) T stage, N stage, and M stage according to the 7th edition AJCC staging system was complete. Besides, clinical variables including age at diagnosis, sex, race, grade, tumor site, laterality, surgery, radiotherapy, and chemotherapy were contained. The exclusion criteria were as follows: (a) survived less than 1 month after diagnosis; (b) patients aged < 18 years; (c) unknown data on race, marital, laterality, surgery, radiotherapy, and chemotherapy. Finally, a total of 1,770 patients met the criteria in the original cohort and 449 patients in the prognostic cohort. Age at diagnosis was divided into under 60 years old, 60–70 years old, and over 70 years old. Tumor grade was grouped into grade I–II, grade III, grade IV, and unknown. All the selected processes of the two study cohorts were exhibited in Figure 1.