Be Aware of the Patient With Benign Follicular Thyroid Lesion Histology and Rising Thyroglobulin Level.

OBJECTIVE

The accurate diagnosis of thyroid follicular/Hürthle cell tumors is challenging and a matter of controversy. We present a series of patients in whom a misclassification of follicular/Hürthle cell thyroid lesions as benign has led to devastating clinical outcomes.

METHODS

The Thyroid Cancer Registry of Rabin Medical Center was screened for patients with metastatic differentiated thyroid carcinoma (DTC) who had been initially diagnosed with benign follicular lesion between 1974 and 2015 and treated with hemithyroidectomy. Clinical, pathologic, and outcome data were collected from the medical files. Adequate pathology specimens, when available, were re-evaluated.

RESULTS

Seven patients met the inclusion criteria. The original pathologic diagnosis was follicular adenoma in 4 patients and Hürthle cell adenoma in 3 patients. Five patients had bone metastases, of whom one also had lung metastases and one, liver metastases. One patient had both cervical and lung metastases, and 1 patient had only meta-static neck lymph nodes. Six patients had a final diagnosis of encapsulated follicular variant of papillary thyroid carcinoma (EFVPTC), and 1 patient was diagnosed as having follicular thyroid cancer metastasis by bone biopsy. In 3 of the patients, capsular invasion was detected retrospectively; only 1 patient had evidence of vascular invasion. All 7 patients had high levels of thyroglobulin at diagnosis of metastatic DTC.

CONCLUSION

Misclassification of follicular thyroid lesions as benign may lead to progressive disseminated DTC. To minimize the clinical risk of misdiagnosis, especially if a thorough evaluation of the specimens by an experienced pathologist is unfeasible, we suggest long-term follow-up of serum thyroglobulin levels.

ABBREVIATIONS: DTC = differentiated thyroid carcinoma; EFVPTC = encapsulated follicular variant of papillary thyroid carcinoma; FVPTC = follicular variant of papillary thyroid carcinoma; NIFTP = noninvasive follicular thyroid neoplasm with papillary-like nuclear features; PTC = papillary thyroid carcinoma.