Thyroid metastasis from lung adenocarcinoma: diagnostic pitfalls and individualized management in a six-patient case series and literature review.

Background: Clinically recognized thyroid metastasis from lung adenocarcinoma is rare and may mimic a primary thyroid malignancy because imaging, cytologic, and immunophenotypic findings overlap. We aimed to characterize the diagnostic pitfalls, management, and outcomes of 6 consecutive patients and to define the limited circumstances in which thyroid-directed treatment may be reasonable. Case Description: Six patients with pathologically confirmed thyroid metastasis from lung adenocarcinoma were treated at an academic tertiary cancer hospital between September 2018 and September 2023. The cohort included 4 men and 2 women, with a mean age of 57 years. Of the 6 patients included in this case series, 2 underwent surgical resection after their primary lung lesions were identified. One of these 2 patients experienced postoperative recurrence with subsequent bone metastasis, and the other developed multiple intrapulmonary metastases and thyroid metastasis after surgery. The remaining 4 patients already had advanced-stage disease at initial detection and were not eligible for surgery, so they received systemic anti-tumor therapy. Thyroid metastasis was detected in all 6 cases during tumor staging or post-treatment follow-up. At the time of examination, 5 patients had no specific clinical symptoms, while 1 patient presented with a palpable neck mass. All patients underwent neck ultrasound and computed tomography (CT) scanning. The diagnosis was confirmed by ultrasound-guided fine-needle aspiration biopsy in 5 patients (Cases 1 and 3-6). In the remaining patient (Case 2), cytological findings were suggestive of primary medullary thyroid carcinoma, and the diagnosis of metastatic lung adenocarcinoma was established by postoperative histopathology following thyroidectomy, which was also performed to prevent local functional impairment. As of the data cutoff date, 1 patient was still alive with disease, 4 patients died from metastatic disease, and 1 patient was lost to follow-up. Conclusions: A new thyroid lesion in a patient with current or previous lung adenocarcinoma should prompt consideration of metastatic disease and tissue confirmation with a focused immunohistochemical panel. Systemic therapy remains the main treatment for most patients. Thyroidectomy should not be routine and may be considered only after multidisciplinary assessment for truly isolated/oligometastatic disease amenable to complete local control or for imminent airway, swallowing, or laryngeal morbidity. No survival benefit from surgery can be inferred from this small series.