Metachronous adenoid cystic carcinoma in the peripheral lung and at base of the tongue.

Primary lung adenoid cystic carcinoma (ACC) is extremely rare and accounts for approximately 0.1%-0.2% of all lung cancers. ACC of the head and neck has generally been regarded as a slow-growing, low-grade malignancy which has a tendency for local recurrence and frequent distant metastasis. When ACC of the lung is identified, physicians must determine whether it represents distant metastasis or a primary lung cancer. Thyroid transcription factor-1 staining is one of the most useful methods to differentiate primary from metastatic lesions in lung cancer. Herein we report a case of metachronous, not synchronous, ACC at the peripheral lung followed by ACC presentation at the base of the tongue, and review of relevant literatures.