Macrofollicular variant of papillary carcinoma, a potential diagnostic pitfall: A report of two cases including a review of literature

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.

A Triumvirate:: Correlating Thyroid Cytopathology, Molecular Testing, and Histopathology

Risk stratification is essential in the preoperative evaluation and management of thyroid nodules, most of which are benign. Advances in DNA and RNA sequencing have shed light on the molecular drivers of thyroid cancer. Molecular testing of cytologically indeterminate nodules has helped refine risk stratification, triage patients for surgery, and determine the extent of surgery. Molecular platforms with high negative predictive values can help identify nodules that may be spared surgery and can be managed conservatively. Here we discuss the importance of integrating cytomorphologic, molecular, and histologic features to help avoid errors and improve patient management.

Reimagining dots and dashes: Visualizing structure and function of organelles for high-content imaging analysis

Organelles are responsible for biochemical and cellular processes that sustain life and their dysfunction causes diseases from cancer to neurodegeneration. While researchers are continuing to appreciate new roles of organelles in disease, the rapid development of specifically targeted fluorescent probes that report on the structure and function of organelles will be critical to accelerate drug discovery. Here, we highlight four organelles that collectively exemplify the progression of phenotypic discovery, starting with mitochondria, where many functional probes have been described, then continuing with lysosomes and Golgi and concluding with nascently described membraneless organelles. We introduce emerging probe designs to explore organelle-specific morphology and dynamics and highlight recent case studies using high-content analysis to stimulate further development of probes and approaches for organellar high-throughput screening.

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.

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.

Comparison of conventional cytology and SurePath in split thyroid fine needle aspiration materials

OBJECTIVE

The aim of the present study was to compare the cytomorphological features and cytopathological diagnoses in thyroid aspiration materials prepared by SurePath® (SP) and conventional cytology (CC).

MATERIALS AND METHODS

Fine needle aspiration (FNA) materials from 180 thyroid nodules were divided into two groups to prepare three conventional smears and one SP slide. Twenty-nine cytomorphological features of thyroid lesions were compared in the CC and SP slides. The Kappa coefficiency was determined for each. The cytopathological diagnosis of CC and SP were compared.

RESULTS

The feature with the lowest Kappa coefficient was the haemorrhagic background, whereas nuclear molding had the highest Kappa coefficient. The rates of the atypical and suspicious cytopathological diagnostic categories were decreased, whereas the rates of benign and malignant categories were increased in SP. When the cytopathological diagnoses of CC and SP were compared with the histopathological diagnoses of the 31 thyroidectomy materials, the results were similar.

CONCLUSION

The common problems seen in CC, such as an excessive number of slides, a haemorrhagic background and air drying artefact in the SP method were not encountered. Through these advantages, the rate of the indeterminate cytopathological diagnosis was low in SP. In addition to those advantages, the increased rates of non-diagnostic cases, the difficulty in evaluating the cytomorphologic features owing to tridimensional structures and the smaller size of the cells and the presence of tridimensional structures uninterpreted microscopically were the disadvantages of SP. The present results showed that SP could be used instead of CC in thyroid cytopathology.

Update on the cytologic features of papillary thyroid carcinoma variants

Papillary thyroid cancer (PTC), which accounts for 85-90% of all thyroid cancers, is generally an indolent tumor with long term survival rates >95%. A reliable definitive diagnosis of PTC is usually straightforward in fine needle aspirates of conventional PTC whenever the characteristic papillary and/or flat honeycomb sheet-like architecture and the typical nuclear features of chromatin pallor, nuclear enlargement, crowding, grooves and pseudoinclusions are encountered. Conventional PTC, however, has diminished in relative frequency as compared to PTC variants, especially the noninvasive follicular variant of PTC, an indolent tumor which has recently been reclassified as "noninvasive follicular thyroid neoplasm with papillary-like nuclear features" (NIFTP). These PTC variants are characterized by various architecture, cell type and shape, and stromal features, some of which can be recognized cytologically. Awareness of the cytomorphological spectrum and of the characteristic cytological features of these PTC variants is important to avoid diagnostic pitfalls. In this article, we review the different variants of PTC, including their cytomorphologic features, differential diagnosis, and salient molecular features. Diagn. Cytopathol. 2017;45:714-730. © 2017 Wiley Periodicals, Inc.