Small cell lung cancer with thyroid gland oligometastasis: A case report.

Extensive disease small cell lung cancer (ED-SCLC) is a systemic disease characterized by diffuse metastases and a poor prognosis. Oligometastatic cases in ED-SCLC are rare. This study reports the case of a 72-year-old Japanese male. A mass lesion was identified on chest computed tomography (CT). Fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT) revealed a solitary thyroid gland lesion with high FDG uptake as an extrapulmonary finding, suggesting thyroid cancer or a goiter. Upon confirmation of diagnosis, treatment of SCLC was prioritized, and chemoradiotherapy for limited disease SCLC was initiated without further examination of the thyroid gland. The thyroid nodule disappeared after treatment. Two years later, the disease recurred, and a thyroid nodule was found to have reappeared. Upon fine needle aspiration cytology of the thyroid, small cell carcinoma was detected. Therefore, in cases of SCLC, it is necessary to carefully investigate the thyroid for solitary lesions to consider the possibility of oligometastasis. KEY POINTS: SIGNIFICANT FINDINGS OF THE STUDY: Manifesting as a solitary lesion, oligometastasis, particularly in the thyroid, is rare in cases of ED-SCLC. WHAT THIS STUDY ADDS: In SCLC cases, it is necessary to carefully investigate the thyroid for solitary lesions to consider the possibility of oligometastasis.