Adenocarcinoma (AC) is the most common type of primary pulmonary malignancy. Lung carcinoid, however, is a rare neuroendocrine tumor. Their coexistence is extremely uncommon. We report the unique case of synchronous advanced lung AC of the right upper lobe (stage IIIB) and typical endobronchial carcinoid tumor in the contralateral lower lobe in a 49-year-old white female who had never smoked. PET-computed tomography scan revealed a fluorine-18-fluorodeoxyglucose-avid AC lesion, whereas the carcinoid tumor was fluorine-18-fluorodeoxyglucose occult. After two lines of platinum-based combination chemotherapies and radiotherapy, the AC progressed, and oral tyrosine kinase inhibitor therapy with erlotinib was initiated in third line. On erlotinib, the AC remained stable for 50 months until disease progression, whereas the carcinoid completely regressed. Molecular testing of the rebronchoscopied AC revealed an exon 19 deletion mutation in the epidermal growth factor receptor (EGFR) gene, whereas the carcinoid was retrospectively EGFR mutation negative. The patient eventually succumbed to ileus caused by intra-abdominal spread of disease, surviving a remarkable 80 months with good performance status throughout most of the follow-up period. To the best of our knowledge, this is the first reported case of synchronous primary lung cancers with different EGFR mutation status, describing an unexpected response of an EGFR-wild-type carcinoid to third-line erlotinib.