Purpose: For treatment decision and prognostic applications, we evaluated p53/epidermal growth factor receptor (EGFR) somatic aberrations in multiple primary lung cancers to differentiate multifocal tumors from intrapulmonary metastasis. Experimental Design: Fifty-eight multiple primary lung cancers of 1,037 patients in a 10-year period were identified to investigate somatic mutations and altered expression of p53 and EGFR for clonality assessment. Genomic DNA was extracted from microdissected cells of paraffin-embedded multiple primary lung cancer tissues. Overexpression and somatic mutations in exons of p53 (exons 5-8) and tyrosine kinase domain of EGFR (exons 18-22) were examined by immunohistochemical staining and DNA sequencing, respectively. Results: High frequency of somatic mutations in p53 (33 of 58, 56.9%) and/or EGFR (44 of 58, 75.9%) resulted in high discrimination rate of tumor clonality (50 of 58, 86.2%) of multiple primary lung cancers. Twenty-two cases (37.9%) were assessed as having the same clonality and 28 cases (48.3%) were determined as having different clonality, which further supported the carcinogenic theory of field cancerization. Notably, the occurrence of lymph node metastasis was more commonly observed in tumors with the same clonality (P=0.045) and was associated with poor patient 5-year survival rate (P=0.001). However, no correlation was found between tumor clonality and patient survival (P=0.630). The EGFR somatic aberrations in 58 multiple primary lung cancers, including vascular invasion associated with EGFR overexpression (P=0.012) and mutation (P=0.025), further suggested the potential benefits of target therapy of inoperable multiple primary lung cancers. Conclusions: Our results suggest that analysis of somatic alterations in p53 and EGFR can significantly improve the clonality assessment and impact management of multiple primary lung cancer patients.
