Cytological features of solid variants of papillary thyroid carcinoma: a fine needle aspiration cytology study of 18 cases

Solid/trabecular subtype of papillary thyroid carcinoma on cytology with focal differentiated high-grade thyroid carcinoma on histology: a cyto-histologic correlation

Solid/trabecular subtype of papillary thyroid carcinoma (S/T PTC) is a rare entity that has been shown to have higher tumour recurrence and mortality rates. A definite diagnosis on fine needle aspiration cytology is often not easy. Rather, this entity may be misdiagnosed in cytology due to a lack of widespread features of classic PTC. We present a case of S/T PTC in a 61-year-old female, showing a focus on differentiated high-grade thyroid carcinoma (DHGTC) on histology. We discuss cytological features with the histologic correlation of S/T PTC and briefly discuss the newly introduced entity, DHGTC.

Solid variant of papillary thyroid carcinoma: an under-recognized entity

Solid variant of papillary thyroid carcinoma (SVPTC) is a rare morphological variant of papillary thyroid carcinoma (PTC). SVPTC is histologically characterized by predominant solid, trabecular and insular nests of tumor cells while cytological features of PTC such as nuclear grooves and nuclear inclusions are preserved. In fine needle aspiration cytology smears, tumor cells of SVPTC may be presented in cohesive, syncytial or trabecular clusters accompanied by some discohesiveness in the absence of necrosis. Although SVPTC and poorly differentiated thyroid carcinoma (PDTC) share similar histological findings of solid nests, SVPTC can be differentiated from PDTC in the lack of tumor necrosis, severe nuclear atypia, and a higher mitotic index. Immunohistochemical expression of CK19 and HBME-1, common markers of PTC, is decreased in solid nests of SVPTC. In pediatric patients exposed to radiation after the Chernobyl nuclear accident, there was a higher prevalence of SVPTC with RET/PTC3 type rearrangement. BRAF mutations are also reported in a small number of adult patients with SVPTC without any prior radiation exposure. Patients with SVPTC may have a slightly higher incidence of metastasis and recurrence of the tumor compared to conventional PTC, although overall survival rate is comparable. In this article, the current knowledge of SVPTC will be reviewed and discussed with an emphasis on the histopathological feature.

Cytologic features of aggressive variants of follicular-derived thyroid carcinoma

Certain carcinomas of the thyroid gland behave aggressively resulting in increased patient morbidity and poor patient prognosis. The diagnosis of these aggressive thyroid cancer subtypes is sometimes challenging and subject to increased interobserver variability. This review deals with the cytological features of such tumors including aggressive variants of papillary thyroid carcinoma, poorly differentiated thyroid carcinoma, and anaplastic thyroid carcinoma. These malignancies fall into 2 groups based on their cytomorphology: those that exhibit distinct microscopic features (eg, nuclear findings typical of classical papillary thyroid carcinoma or marked anaplasia) and those that present with more subtle cytologic features (eg, nuclear pseudostratification, "soap bubble" nuclei, supranuclear or subnuclear cytoplasmic vacuoles, rosette-like structures, hobnail cells). We review the literature regarding these aggressive thyroid cancers and highlight important phenotypic characteristics that can be useful for their diagnosis based on fine needle aspiration.

Solid papillary thyroid carcinoma with Hashimoto's thyroiditis: description of a further case with challenging cytological features

Solid papillary thyroid carcinoma (SV-PTC) is a rare variant which is mainly observed in young patients with a history of exposure to ionising radiations. Neoplasms belonging to such category generally carry RET-PTC (REarranged during Transfection- Papillary Thyroid Carcinoma) fusions and seem to have a slightly worse prognosis with respect to classical and follicular variants of papillary thyroid carcinoma (PTC), though consistent prognostic and survival data are scarce. SV-PTC should be differentiated from trabecular-insular poorly differentiated thyroid carcinomas, which occur in a different age group and carry a dismal prognosis. These latter tumours do not show the typical nuclear features of PTC and show tumour necrosis with an high mitotic activity. In this report a further case of SV-PTC is described which was associated to Hashimoto's thyroiditis, a finding never described in the cytological literature up to now for SV-PTC; this association created further differential diagnostic problems. The neoplasm displayed RET-PTC1 fusion.

Cytopathology of Solid Variant of Papillary Thyroid Carcinoma: Differential Diagnoses with other Thyroid Tumors

OBJECTIVES

Solid variant of papillary thyroid carcinoma (SVPTC) is rare, differing from classical PTC (cPTC) in architecture and outcome. We evaluated the cytomorphology of SVPTC cases to assess the feasibility of a preoperative diagnosis.

STUDY DESIGN

SVPTC cases were evaluated for architecture, nuclear features, and Bethesda category and were compared with noninvasive follicular thyroid neoplasm with papillary-like nuclear features/follicular variant of PTC (NIFTP/FVPTC), cPTC, and poorly differentiated thyroid carcinoma (PDTC).

RESULTS

Nine SVPTCs, 29 NIFTP/FVPTCs, 12 cPTCs, and 4 PDTCs were included. The predominant architecture in most SVPTCs was solid fragment, which is helpful in differentiating them from NIFTP/FVPTC (p < 0.001) and cPTC (p = 0.006) but not from PDTC. The presence of microfollicles led to misinterpretation as NIFTP/FVPTC/follicular neoplasm in 4 patients. All but 1 SVPTC showed diffuse nuclear features. Intranuclear pseudoinclusions (INIs) were seen in 67% of SVPTCs as compared to 83% of cPTCs, 14% of NIFTP/FVPTCs (p = 0.005), and none of PDTCs. SVPTC cases were commonly (78%) categorized as intermediate/suspicious.

CONCLUSIONS

The presence of solid fragments and lack of true papillae are helpful in differentiating SVPTC from cPTC. Solid fragments, trabeculae, the extent of nuclear features, and INIs should be looked for in cases with prominent microfollicles for distinguishing SVPTC from NIFTP/FVPTC. None of the features were helpful in differentiating SVPTC from PDTC.

Recent Advances in the Classification of Low-grade Papillary-like Thyroid Neoplasms and Aggressive Papillary Thyroid Carcinomas: Evolution of Diagnostic Criteria

Papillary thyroid carcinomas account for ∼80% of well-differentiated thyroid tumors. During the past decade, several new variants of papillary-like thyroid neoplasms and papillary thyroid carcinomas have been recognized. Some of these neoplasms that were previously classified as malignant have been reclassified as low-grade neoplasms, as the diagnostic criteria have evolved. Similarly, some of the papillary thyroid carcinomas that were previously classified as conventional or classic papillary thyroid carcinomas have now been recognized as more aggressive variants of papillary thyroid carcinomas. Recognizing these differences becomes more important for the proper medical, surgical, and radiotherapeutic management of patients with these neoplasms.

[DICER1 mutated, solid/trabecular thyroid papillary carcinoma in an 11-year-old child]

We report the case of an 11-year-old patient diagnosed with a solid variant of papillary thyroid carcinoma. Papillary thyroid carcinoma (PTC) is the most common thyroid cancer, representing 80-90% of all newly diagnosed thyroid cancers. Among the many variants described, solid/trabecular variant of papillary thyroid carcinoma is a rare entity and account for 3% of thyroid cancers. It is more common in children and young adults, and it is seen in higher proportion in post radiation papillary thyroid carcinoma cases. Histologically, solid variant papillary carcinoma is characterized by a predominantly solid, trabecular or insular growth pattern, and the presence of cytological features typical of PTC. Its main differential diagnosis is poorly differentiated thyroid carcinoma. It has a less favorable prognosis than the classical papillary type, with a higher risk of distant metastasis, extrathyroidal extension and lympho-vascular invasion. It is associated with a slightly lower long-term survival in adult cases, but not in children. The management of solid variant PTC includes surgery, associated or not with postoperative radioiodine ablation, according to the aggressiveness criteria. Our patient had a DICER1 somatic mutation. Carriers of germline DICER1 mutations are predisposed to a rare cancer syndrome, the DICER1 syndrome, with a higher risk of numerous tumors and infrequently differentiated thyroid carcinomas.

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.