Then, we extracted 101–133 bp and 134–500 bp fragment size information from BAM files for each sample and analyzed the sequencing depth distribution of three common cancer genes, ALK receptor tyrosine kinase (ALK), epidermal growth factor receptor (EGFR) and erb-b2 receptor tyrosine kinase 2 (ERBB2). The gene discussed is EGFR; the disease is cancer.