The incidence of human epidermal growth factor receptor 2 (Her-2) mutations in lung adenocarcinoma is approximately 3%; however, its significance in the management of these lung cancers remains under investigation. We describe an incidental but unique opportunity to evaluate the response to treatment with herceptin in a patient with bilateral synchronous lung primaries in conjunction with breast carcinoma. Interval imaging following surgical resection of the squamous cell carcinoma while on herceptin treatment delineated the radiological regression of the Her-2 positive lung adenocarcinoma. We feel that this case highlights the potential role for herceptin treatment in Her-2 positive lung adenocarcinomas and demonstrates the importance of screening for these mutations.