Lung cancer, thyroid cancer or both: An unusual case presentation.

Cancer metastasis to the thyroid is rare. Primary sites that have been reported to metastasize to the thyroid gland include breast and kidney. There are very few case reports describing metastasis of a lung primary cancer to the thyroid gland. We describe a case of a never-smoker patient with metastatic adenocarcinoma of the lung and a malignant thyroid mass presenting simultaneously. The thyroid biopsy could not distinguish whether it was a metastasis or incidentally found thyroid primary carcinoma. Based on EGFR mutational status it was determined that he has a primary lung cancer and thyroid metastasis. He was started on erlotinib and has had a marked response in both the lung and the thyroid masses. The presence of mutations within the EGFR gene can help distinguish lung adenocarcinoma from other carcinomas like thyroid cancer. This is the first published case of primary lung adenocarcinoma with metastasis to thyroid and with EGFR mutation.