Diagnostic pitfalls and therapeutic outcomes of the macrofollicular variant of papillary thyroid carcinoma

BACKGROUND: The macrofollicular variant of papillary thyroid cancer (MFVPTC) is a rare histological variant of papillary thyroid cancer (PTC), with only 71 cases reported through 2014. This study analyzed the clinical, preoperative thyroid ultrasonography (US), and fine needle aspiration cytology (FNAC) features; and therapeutic outcomes of 11 patients with MFVPTC. METHODS: The records of 393 patients with histologically diagnosed follicular variant of papillary thyroid carcinoma (FVPTC), including 11 with MFVPTC, were retrospectively reviewed. Preoperative thyroid US findings, clinical presentation, treatment outcomes, and survival rates were analyzed. RESULT: Mean tumor size was significantly greater in patients with MFVPTC than that in those with FVPTC (4.2 ± 2.1 cm vs. 2.9 ± 1.7 cm; p = 0.016). No patient with MFVPTC had lymph node involvement, but one had a micrometastasis to the lung, which responded well to therapeutic radioiodine. All MFVPTC lesions were isoechoic on US. Eight nodules had calcifications and eight had irregular margins. FNAC showed that these tumors had low cellularity, absence or focal presence of enlarged clear nuclei, and subtle or focal nuclear features of PTC. Cells were, arranged in microfollicular pattern, with abundant colloid background. Multifocal PTCs were detected in the opposite lobe of two patients. All 11 patients with MFVPTC had excellent outcomes. No patient experienced recurrence, and survival rates were high. CONCLUSIONS: Malignant US criteria combined with FNAC features have a low preoperative diagnostic rate for MFVPTC. Surgery is recommended for patients with thyroid nodules larger than 4 cm and those with subtle and focal atypical nuclei in FNAC.