ESR1 and tumor of uterus: To determine whether the lung nodules were metastases from the uterine tumors or independent lung lesions, we performed immunohistochemistry (IHC) on cross-sections of the lung nodules and uterine tumors using estrogen receptor alpha (ERα) as a uterine cell marker and transcription termination factor (TTF1) as a lung cell-specific marker (Fig. 2g–n).