Third, it is unclear whether alterations in serum tumor marker levels actually represent the intratumor heterogeneous components in each patient, although Tanaka et al. found that EGFR-TKI efficacy in EGFR-mutated patients depended on the initial Cyfra21-1 level and concluded this represented a squamous-rich component in NSCLC [8]. Here, EGFR is linked to non-small cell lung carcinoma.