Endocrine Abstracts

Introduction: Metastases to the thyroid are rare (1.4–3% of malignant solid tumors). When present, metastatic cancers mimic the ultrasound image of the thyroid parenchyma, hindering diagnosis. Breast cancer rarely metastasizes to the thyroid.

Case: A 61-year-old woman was referred for goiterin the context of post-surgery evaluation for breast cancer. Thyrotropin (1.14 mIU/l), calcitonin (0.5 pg/ml) and parathyroidhormone (54 pg/ml) levels were normal. Thyroid ultrasound (US) showed a multinodular goiter with maximum nodule size of 4.2 cm at the left thyroid lobe (isoechoic with cystic degeneration areas, with few coarse calcifications and poor peripheral vascularization), scattered smaller hypoechoic nodules up to 4 mm in both lobes and few colloid cystsup to 7 mm, without abnormal lymph nodes. An US-guided FNA was performed at the largest left thyroid lobe nodule, showing benign nodular hyperplasia (Bethesda II). The patient was monitored by US and thyroid hormone testing. Elevated tumormarkers (Ca15–3) led to 18-FDG PET-CT scanning, following oncology consultation. Abnormal uptake (SUV max: 3.7) was noted in the area corresponding to the largest noduleat the left thyroid lobe. Total thyroidectomy was recommended (1.5 years after initial FNA). Histopathological examination revealed the presence of neoplastic infiltration in off-white areas of the right lower lobe of solid carcinoma with morphological and immunophenotypic characteristics compatible with breast tissue origin [CK8–18(+), CK19(+), GATA-3(+), ER(+ >80%), PGR(–), TTF-1(–), Thyroglobulin(–), p40(–), HBME-1(–), Galectin-3(–), S-100(–), Calcitonin(-), Ki67~30%].

Conclusion: In this patient, although FNA had been performed in the larger nodule that had the most suspicious featuresfor possible malignancy, it was considered that the increase in tumor markers and concomitant abnormal uptake in 18-FDG PET-CT increased the likelihood of cancer metastasis. However, histopathology after thyroidectomy revealed breast tissue metastasis in off-white areas at the right lower lobe where ultrasound had noted small hypoechoic nodules and colloid cysts. Although thyroid metastases are not very common, caution should be given especially when thyroid parenchyma lesions coexist with a recent history of malignancy.