Differential gene expression for breast cancer lung metastasis versus primary breast cancer. Genes with significant down- and upregulation are indicated in blue and red, respectively (adjusted P < .05). Different patterns of gene expression changes are observed, with (A) significantly more changes in the luminal A subtype compared with (B) high-risk tumors (lumB, Human epidermal growth factor receptor 2 (HER2)–enriched, Basal-like). Within the luminal A subtype, gene expression changes were mostly confined to (C) tumors with subtype switch in lung metastasis compared with (D) nonswitched metastases.