Summary

A 34-year-old woman—a diagnosed case of pT1N1MO, stage IIa, estrogen and progesterone receptor positive (ER, PR) positive, Her2 negative carcinoma of the left breast—was managed with modified radical mastectomy and adjuvant chemotherapy. While planning for radiotherapy, she was found to have a well-defined enhancing lesion with spiculated margins in the superior segment of the right lower lobe along with a heterogeneously enhancing right hilar lymph node on CT. Histopathological evaluation of the lesion was suggestive of adenocarcinoma. The lesion was negative for ER, PR receptors, mammoglobin and gross cystic disease fluid protein. Thyroid transcription factor 1 (TTF-1) was positive, suggesting a primary lung adenocarcinoma rather than metastatic lesion from the breast. This case clearly signifies the importance of histopathological diagnosis of suspicious metastatic lesions in the setting of early breast cancer. We would also like to highlight the importance of TTF-1 in differentiating primary lung malignancy from metastasis.