Three cases of macrofollicular variant of papillary thyroid carcinoma

Macrofollicular subtype of papillary thyroid carcinoma: Ultrasonographic findings and clinical implications

The macrofollicular subtype of papillary thyroid cancer (MFS-PTC) is a rare subtype often leading to a challenging diagnosis. To evaluate the ultrasonographic (US) features and clinical implication of MFS-PTC. Records of 14 patients histologically diagnosed with MFS-PTC at our institution over a period of 16 years were retrospectively reviewed. Preoperative US features, Bethesda categories determined by fine-needle aspiration (FNA) or core needle biopsy (CNB), and final pathology were assessed in all patients with MFS-PTC. Of the 14 MFS-PTC cases, most nodules were noted as smooth marginated, solid or predominantly solid isoechoic on US and were categorized as low suspicion in 12 cases and intermediate suspicion in 2 cases. The median tumor size was 1.2 cm (range, 0.6-5.6 cm). Of 11 cases that underwent FNA or CNB, 4 (36.4%) with Bethesda category II or III underwent the follow-up because of benign-looking appearance on US and benign results in subsequent CNBs. However, the patients underwent delayed surgery (31.3 months, range 12-41 months) because of serially increased tumor size. Seven patients diagnosed with Bethesda type IV, V, and VI subsequently underwent surgery. Gross extrathyroidal extension into subcutaneous fat tissue and lateral lymph node metastasis were noted in a patient who underwent follow-up. No distant metastases or recurrence was detected. MFS-PTC is representative of a benign sonographic appearance of PTC subtypes. Tumor growth on serial US images is the only suspicious finding for MFS-PTC because FNA or CNB is often false negative.

Macrofollicular Architecture in Invasive Encapsulated Follicular Variant of Papillary Thyroid Carcinoma: A Pitfall in Thyroid Practice

BACKGROUND

Predominantly macrofollicular architecture in invasive encapsulated follicular variant of papillary thyroid carcinoma (IEFVPTC-MF) is rare and often a cause of misinterpretation during pre-operative work-up and histopathology evaluation. We comprehensively evaluated the radiological, cytological, gross, microscopic, molecular and follow-up characteristics of four such cases, intending to increase its recognition and add our experience to the limited literature available.

METHODS

All such histopathologically-proven cases of IEFVPTC-MF were retrieved from the departmental archives. The clinical details, thyroid ultrasound, cytology and thyroid scan findings were reviewed. Allele-specific PCR for BRAF p.V600E, KRAS, NRAS, and HRAS mutations, and FISH assays for ETV6::NTRK3 fusion and RET fusions were performed.

RESULTS

There were four cases of IEFVPTC-MF diagnosed between 2021 and 2022, involving two males and two females. The median age at presentation was 27 years, and the duration of the disease was 1-10 years. Thyroid ultrasound was TR1 (benign; n = 1), TR2 (not suspicious; n = 2), or TR4 (moderately suspicious; n = 1). Cytology was categorized as nondiagnostic (n = 1), benign (n = 1), and atypia of undetermined significance (n = 1). The three nodules with available cytology smears showed abundant colloid. Cells were arranged as sheets/microfollicles/clusters. Nuclei were predominantly round with minimal/focal elongation, membrane irregularity, and cellular crowding. On gross examination, cut surfaces of the tumors showed variable amounts of colloid. The tumors were solid-cystic. Histopathology revealed partially encapsulated multinodular tumors. There were prominent pseudopapillae projecting into the lumina of macrofollicles. Nuclei were predominantly round with variable nuclear atypia, including chromatin clearing and multifocal presence of nuclear grooves. Pseudoinclusions were identified in two. Molecular analysis revealed NRAS codon 61 mutation and ETV6::NTRK3 fusion in one case each. Two patients had cervical lymph node and hematogenous metastases. Post-radio-active iodine, the response was structurally incomplete (n = 2), indeterminate (n = 1) and excellent (n = 1).

CONCLUSIONS

Macrofollicular architecture in invasive encapsulated follicular variant of papillary thyroid carcinoma is a major pitfall in thyroid oncology practice. Long-standing disease, and ultrasonographic and cytological features that overlap with benign disease, often lead to underdiagnosis during pre-operative evaluation. As patients may consequently develop distant metastases and have inadequate treatment response, there is a need for more vigilant understanding of the spectrum of macrofollicular thyroid disease for accurate diagnosis. ETV6::NTRK3 or other fusions, when found, present opportunities for targeted therapy.

Macrofollicular variant of papillary thyroid carcinoma with metastasis to femur

Background

Macrofollicular variant of papillary thyroid carcinoma (MFV-PTC) is a rare subtype with histological features and an indolent clinical course that can be confused with nodular goiter or follicular adenoma. However, on rare occasions it may show more aggressive biological behavior. Only two cases of MFV-PTC with bone metastases have been reported previously. We describe the clinical-pathological characteristics of a man with MFV-PTC that developed femur metastasis. This the first case of MFV-PTC with femur metastases diagnosed histologically by means of an image-guided core needle biopsy in English literature.

Case presentation

A 33-year-old man presented two years earlier with swelling in the right neck associated with weight loss and pain in the left knee. Neck ultrasonography showed hyperechogenic and hypogenic nodular images in the thyroid's right lobe. A fine needle aspiration biopsy specimen was initially interpreted as nodular hyperplasia. A CT showed a large tumor involving right thyroid lobe with trachea and vascular structures displaced to the right, and a total thyroidectomy was performed. Subsequently, a MRI of the knee confirmed the presence of a destructive tumor in the femur. A guided core-needle biopsy of the knee tumor showed the presence of metastatic MFV-PTC. Re-assessment of the histology from thyroidectomy was also consistent with MFV-PTC. A whole-body ¹⁸F-FDG PET/CT showed presence of lesions in the left anterior costal arch, metaphysis of the left femur and in the sternum handle. Therefore, he received 200 mCi radioactive iodine, and 40 Gy of radiotherapy to left costal arches and knee, which decreased his symptoms. Currently, after 10 months of follow-up, the patient is alive with bone tumor activity.

Conclusions

Our case supports the view that, on rare ocassions, MFV-PTC may show a more aggressive biological behavior than expected. The synchronous or asynchronous presence of one or more bone lesions, should raise the suspicion of metastasis. Given the suspicion, it is necessary to take a biopsy to confirm histologically. Only a careful analysis of the architectural and cytological characteristics of goiter or hyperplastic nodules will allow to recognize this rare variety of carcinoma.

Macrofollicular variant of papillary thyroid carcinoma with extensive lymph node metastases

The macrofollicular variant of papillary thyroid carcinoma is a rare subtype of the follicular variant of papillary thyroid carcinoma and is usually characterized by an indolent clinical course. The tumors are prone to be misdiagnosed as benign due to their macrofollicular architecture and bland cytologic features. We report a rare case of the macrofollicular variant of papillary thyroid carcinoma with extensive lymph node metastases. The patient was a 48-year-old female with a right thyroid nodule and multiple enlarged lymph nodes in the right neck. It was not possible to make a definitive diagnosis of malignancy on fine-needle aspiration cytology and intraoperative frozen section. She underwent total thyroidectomy with right modified radical neck dissection. The surgical specimen showed a 2.5 × 1.5 × 10 cm, well-circumscribed macrofollicular variant of papillary thyroid carcinoma in the right lobe and multiple central and right lateral neck lymph node metastases. Molecular testing for BRAF, NRAS, HRAS, and KRAS was all negative. We then reviewed the demographic and clinicopathologic characteristics of 71 patients with the macrofollicular variant of papillary thyroid carcinoma. The cytologic or histopathologic diagnosis of macrofollicular variant of papillary thyroid carcinoma can be difficult. Extensive lymph node metastases caused by the macrofollicular variant of papillary thyroid carcinoma may occur even in the absence of capsular or lymphovascular invasion. This review will help to better understand the nature of the macrofollicular variant of papillary thyroid carcinoma.

Remarkable response to radioiodine therapy in a case of metastatic macrofollicular variant of papillary thyroid carcinoma

Macrofollicular variant is a rare variant of papillary thyroid carcinoma. Although they are usually associated with a good prognosis, aggressive forms have been described. Distinction from an adenomatous goiter or follicular adenoma is often difficult and can lead to misdiagnosis. We report a metastatic macrofollicular variant of papillary thyroid carcinoma with a remarkable clinical, biochemical, and structural response to radioiodine treatment.