Clinicopathological features of incidentally detected metastatic thyroid papillary carcinoma in cervical lymph nodes of non-thyroid cancer patients: a retrospective analysis of 31cases.

Background: The incidental finding of thyroid inclusions in lymph nodes of neck dissections of non-thyroid cancer patients is an unusual event. It is still controversial for pathologists about whether this represents benign inclusions or metastatic papillary thyroid carcinoma (PTC). This study is to analyze clinicopathological features of such cases in an attempt to explore their clinical implications.

Methods: Pathological data were searched for incidentally detected PTC of cervical lymph nodes in non-thyroid cancer cases. Clinicopathological characteristics were reevaluated and recorded. BRAF V600E protein expression and sequencing analysis was then performed in cases with sufficient tissues.

Results: 31 patients had an incidental finding of PTC in lymph nodes of patients with non-thyroid cancer. BRAF immunohistochemical staining were performed in 17 metastatic lymph nodes with sufficient tumor tissues, and 6 were positive. BRAF V600E point mutation was detected in 5 of 6 BRAF V600E positive cases. Subsequent imaging examinations of the thyroid showed no nodules or calcifications/benign nodules in 20 patients, and suspected malignant nodules in 5 patients. 12 patients underwent total thyroidectomy or ipsilateral lobectomy, and 6 showed PTC in postoperative pathological examinations. The remaining 19 patients without surgery were kept under active surveillance, and no one had recurrence of PTC.

Conclusion: Incidentally discovered PTC in lymph nodes has usually interpreted as metastasis from a clinical occult thyroid primary cancer, but primary PTC was not always detected. This suggests it could be double occult lesions. With regards to concurrence with highly malignant tumor, most patients could keep regular surveillance.