Molecular profile and clinical-pathologic features of the follicular variant of papillary thyroid carcinoma. An unusually high prevalence of ras mutations

The follicular variant (FV) of papillary thyroid carcinoma is characterized by a follicular growth pattern and cytologic features of papillary carcinoma. ret/PTC rearrangements are common in classic papillary thyroid carcinoma (PTC) and PAX8-PPAR gamma and ras mutations in follicular thyroid carcinoma. Their prevalence in FV has not been established. We studied these genetic alterations and clinical-pathologic features in 30 FV cases and compared those with 46 non-FV papillary carcinomas. FV cases revealed 1 ret/PTC rearrangement (3%) and 13 ras mutations (43%). Non-FV cases harbored 13 ret/PTC (28%) (P = .006) and no ras mutations (P = .0002). No PAX8-PPAR gamma was found in either group. FV cases demonstrated a significantly higher prevalence of tumor encapsulation, angiovascular invasion, and poorly differentiated areas and a lower rate of lymph node metastases. These data indicate that the FV of papillary carcinoma has a distinct set of molecular alterations and is characterized by a high frequency of ras point mutations.     

Correlation between BRAF mutation and the clinicopathological parameters in papillary thyroid carcinoma with particular reference to follicular variant

Mutation of the BRAF gene is common in thyroid cancer. Follicular variant of papillary thyroid carcinoma is a variant of papillary thyroid carcinoma that has created continuous diagnostic controversies among pathologists. The aims of this study are to (1) investigate whether follicular variant of papillary thyroid carcinoma has a different pattern of BRAF mutation than conventional papillary thyroid carcinoma in a large cohort of patients with typical features of follicular variant of papillary thyroid carcinoma and (2) to study the relationship of clinicopathological features of papillary thyroid carcinomas with BRAF mutation. Tissue blocks from 76 patients with diagnostic features of papillary thyroid carcinomas (40 with conventional type and 36 with follicular variant) were included in the study. From these, DNA was extracted and BRAF V600E mutations were detected by polymerase chain reaction followed by restriction enzyme digestion and sequencing of exon 15. Analysis of the data indicated that BRAF V600E mutation is significantly more common in conventional papillary thyroid carcinoma (58% versus 31%, P = .022). Furthermore, the mutation was often noted in female patients (P = .017), in high-stage cancers (P = .034), and in tumors with mild lymphocytic thyroiditis (P = .006). We concluded that follicular variant of papillary thyroid carcinoma differs from conventional papillary thyroid carcinoma in the rate of BRAF mutation. The results of this study add further information indicating that mutations in BRAF play a role in thyroid cancer development and progression.     

Diffuse sclerosing variant of papillary thyroid carcinoma: lack of BRAF mutation but occurrence of RET/PTC rearrangements.

Diffuse sclerosing variant of papillary thyroid carcinoma (PTC) is a rare tumour with a characteristic morphology as well as a strong preponderance for younger female patients. The T1799A missense mutation in exon 15 of the BRAF gene and RET/PTC rearrangement have been identified as the dominant genetic tumour initiation events in the pathogenesis of PTC leading to a constitutive activation of the RAS-RAF-MAPK pathway. In order to elucidate the pathogenesis of diffuse sclerosing variant of PTC, the prevalence of BRAF mutation and RET/PTC were determined by RT-polymerase chain reaction and DNA-sequence analysis in tumour samples of seven patients with this variant (all female, age range 15-61 years, mean 33.3 years) without prior radiation exposure. None of these cases showed a BRAF mutation. RET/PTC1 (two out of seven) and RET/PTC3 (one out of seven), which have been shown in large PTC series to comprise together more than 90% of RET/PTC types, were found in <50% of the cases investigated. All seven samples expressed the RET tyrosine kinase domain but lacked its extracellular domain potentially suggesting the existence of rare types of RET/PTC rearrangement in the four remained cases of diffuse sclerosing variant of PTC. Regarding this subtype, our study confirmed the paradigm of a mutual exclusivity between RET/PTC and BRAF in PTC. Additionally, this rare variant of papillary thyroid carcinoma may represent a tumour type susceptible to RET-targeted therapies.     

The triage efficacy of fine needle aspiration biopsy for follicular variant of papillary thyroid carcinoma using the Bethesda reporting guidelines

Diagnosis of follicular variant of papillary thyroid carcinoma (FVPTC) by ultrasound-guided fine-needle aspiration (FNA) is challenging. In this retrospective review, we evaluated triage efficacy (i.e., potential for triggering surgical intervention) in 44 archived FNA biopsies of surgically confirmed FVPTC obtained between December 2006 and December 2008. We compared the original FNA diagnoses with reclassified diagnoses based on 2007 National Cancer Institute (NCI)/Bethesda recommendations, and reviewed FNA cytologic features. Original FNA diagnoses included colloid nodule (7%, 3/44), atypical follicular cells (5%, 2/44), follicular lesion (11%, 5/44), follicular neoplasm (16%, 7/44), suspicious for malignancy/PTC (27%, 12/44), and papillary thyroid carcinoma (34%, 15/44). Reclassified diagnoses included indeterminate (5%, 2/44), colloid nodule (7%, 3/44), atypical cells of undetermined significance [ACUS] (7%, 3/44), Hurthle cell neoplasm (2%, 1/44), follicular neoplasm (7%, 3/44), suspicious for malignancy/PTC (25%, 11/44), and PTC (48%, 21/44). Triage efficacy was 77% (34/44) for original diagnoses versus 82% (36/44) for reclassified FNA diagnoses. We frequently observed cytologic features of PTC, such as nuclear grooves and fine chromatin; conversely, intranuclear inclusions, though present in 77% cases, were scant. Our review findings suggest that lack of characteristic cytologic features of PTC,coexistence with other thyroid lesions, and small tumor size arethe major obstacles to FNA diagnosis of FVPTC. Reclassification of thyroid FNA diagnoses does not significantly improve triage efficacy. Furthermore, FNA diagnoses of follicular neoplasm and suspicious for malignancy are valuable in patients with FVPTC because they trigger triage toward surgical intervention.     

Sensitive cytologic criteria for the identification of follicular variant of papillary thyroid carcinoma in fine-needle aspiration biopsy

The cytologic diagnosis of follicular variant of papillary thyroid carcinoma (FVPTC) can be extremely challenging and may be associated with false negative diagnoses. The purpose of this study was to determine the minimal cytologic criteria needed to identify FVPTC. We examined sixty-nine fine-needle aspiration (FNA) cases, processed with Diff-Quik and Papanicolaou stains, that were either diagnostic or suspicious of FVPTC. All cases had histologic confirmation. These cases included 29 FVPTC, 18 classic papillary thyroid carcinoma (PTC), 17 follicular neoplasm (6 adenomas, 10 carcinomas, 1 neoplasm NOS), 2 lymphocytic thyroiditis and 3 nodular goiter. Seven of the most commonly cited cytomorphologic features, including flat syncytial sheets, nuclear enlargement, fine chromatin, nuclear grooves, nuclear pseudoinclusions, and amount of colloid and cytoplasm, were evaluated. A diffuse distribution of fine chromatin, nuclear grooves, and colloid was seen more often in FVPTC than in follicular neoplasm (p<0.01). The combination of flat/syncytial sheets, nuclear enlargement, and fine chromatin was observed in all our cases of FVPTC, and is therefore considered a sensitive marker in detecting FVPTC. Logistic regression analysis revealed colloid to be the only positive predictor in favor of FVPTC over classic PTC.     

Follicular variant of papillary thyroid carcinoma: genome-wide appraisal of a controversial entity

The majority of thyroid tumors are classified as papillary (papillary thyroid carcinomas; PTCs) or follicular neoplasms (follicular thyroid adenomas and carcinomas; FTA/FTC) based on nuclear features and the cellular growth pattern. However, classification of the follicular variant of papillary thyroid carcinoma (FVPTC) remains an issue of debate. These tumors contain a predominantly follicular growth pattern but display nuclear features and overall clinical behavior consistent with PTC. In this study, we used comparative genomic hybridization (CGH) to compare the global chromosomal aberrations in FVPTC to the PTC of classical variant (classical PTC) and FTA/FTC. In addition, we assessed the presence of peroxisome proliferator-activated receptor-gamma (PPARG) alteration, a genetic event specific to FTA/FTC, using Southern blot and immunohistochemistry analyses. In sharp contrast to the findings in classical PTC (4% of cases), CGH analysis demonstrated that both FVPTC (59% of cases) and FTA/FTC (36% of cases) were commonly characterized by aneuploidy (P = 0.0002). Moreover, the pattern of chromosomal aberrations (gains at chromosome arms 2q, 4q, 5q, 6q, 8q, and 13q and deletions at 1p, 9q, 16q, 17q, 19q, and 22q) in the follicular variant of PTC closely resembled that of FTA/FTC. Aberrations in PPARG were uniquely detected in FVPTC and FTA/FTC. Our findings suggest a stronger relationship between the FVPTC and FTA/FTC than previously appreciated and support further consideration of the current classification of thyroid neoplasms.     

A subset of the follicular variant of papillary thyroid carcinoma harbors the PAX8-PPARgamma translocation

The occurrence of the PAX8-PPARgamma fusion gene is thought to be restricted to follicular tumors (adenomas and carcinomas) of the thyroid (FTA and FTC). Using interphase fluorescent in situ hybridization (FISH), together with recombinant tissue-type polymerase chain reaction (RT-PCR) and immunohistochemistry, we detected the PAX8-PPARgamma translocation in 4 of 8 cases of the follicular variant of papillary thyroid carcinoma (FVPTC) exclusively or almost exclusively (>95%) composed of follicles. The 4 tumors with the translocation were larger and apparently more invasive than the remaining tumors, but the series is too small to allow a statistically meaningful comparison of the data. Our findings show that follicular thyroid carcinoma (PTC) may also harbor the PAX8-PPARgamma fusion gene and indicate that a subset of FVPTC shares some molecular features of FTA and FTC.     

Diffuse (or multinodular) follicular variant of papillary thyroid carcinoma: a clinicopathologic and immunohistochemical analysis of ten cases of an aggressive form of differentiated thyroid carcinoma

In an attempt to advance and improve the characterization of the so-called diffuse follicular variant of papillary thyroid carcinoma (diffuse FVPTC) we studied a series of 59 thyroid carcinomas consecutively treated in a specialized center. The clinicopathologic and some of the immunohistochemical characteristics (uPA-R, Lewis X, Sialyl Lewis X, and MIB-1) of ten cases of FVPTC displaying a multinodular or diffuse pattern of growth, and histologic features similar to those previously described in diffuse FVPTC, were compared with those of common papillary thyroid carcinoma (PTC, 25 cases) and common FVPTC (8 cases). Cases of diffuse FVPTC differed significantly from common PTC and FVPTC in targeting younger patients and in exhibiting a prevalence of multicentricity, extrathyroid extension, nodal metastasis, and vascular invasion. Immunohistochemically, diffuse FVPTC cases were characterized by the overexpression of uPAR and sialyl Lewis X. No differences were observed regarding MIB 1 immunoreactivity. Regardless of the term used to designate the multicentric, invasive form of FVPTC (diffuse or multinodular FVPTC) it is crucial to acknowledge the existence of cases of FVPTC with a guarded prognosis that should be distinguished from the classic, uninodular form of FVPTC.     

Galectin-3 is highly expressed in nonencapsulated papillary thyroid carcinoma but weakly expressed in encapsulated type; comparison with Hector Battifora mesothelial cell 1 immunoreactivity

The histologic diagnosis of the follicular variant of papillary thyroid carcinoma (FVPTC) may be troublesome, especially in its encapsulated form. We evaluated the expression of galectin-3 (gal-3) and Hector Battifora mesothelial cell (HBME-1) in 200 formalin-fixed thyroid tissues with diagnosis of classical variant of papillary thyroid carcinoma or FVPTC, encapsulated or with infiltrative growth, with or without lymph node metastasis. All cases of classical variant of papillary thyroid carcinoma were consistently positive for gal-3; similar results have been obtained by using HBME-1. Interestingly, the invasive type of FVPTC, with or without metastasis, was strongly positive for gal-3 (78.2% and 96%, respectively), whereas only 46.8% of encapsulated FVPTCs without metastasis showed immunostaining for this marker. In the latter group, the HBME-1 expression achieved a significantly higher percentage of positivity (87%). Surprisingly, gal-3 immunodetection showed negative results in 4 encapsulated FVPTCs, despite the strong immunoreactivity in corresponding metastasis. Our data suggest that gal-3 immunodetection alone is not able to support the diagnosis of encapsulated FVPTCs.     

Thyroid nodules with FNA cytology suspicious for follicular variant of papillary thyroid carcinoma: follow-up and management

Thyroid nodules diagnosed as follicular neoplasm on fine-needle aspiration biopsy (FNAB) may represent hyperplastic/adenomatous nodules, follicular adenoma or carcinoma, and follicular variants of papillary thyroid carcinoma (FVPTC) on histologic follow-up. In our laboratory, we attempted to identify a subset of cases which showed cellular specimens with focal features (nuclear chromatin clearing, membrane thickening, and rare grooves) suspicious for the follicular variant of papillary thyroid carcinoma. These cases are reported as follicular-derived neoplasms with nuclear features suspicious for FVPTC to distinguish them from those diagnosed as follicular neoplasm. This study documents our experience with 52 cases so diagnosed and followed prospectively with histologic follow-up. A neoplastic nodule was confirmed in 45/52 cases (86%), of which 40 were malignant (77%). FVPTC was identified in 35/52 cases (67%). Four cases were usual papillary carcinoma, 3 were follicular adenoma, 2 were Hürthle-cell adenoma, and 1 was insular carcinoma. In 7 cases, the subsequent histologic findings were nonneoplastic (5 hyperplastic nodules and 2 colloid nodules). Our prospective study shows that in cellular smears from thyroid nodules, a careful search for the nuclear features of papillary carcinoma should be performed, and it is appropriate to diagnose cases as suspicious for FVPTC if the nuclear features of papillary carcinoma are focal. The surgical management of this group may include an intraoperative confirmation of cytologic diagnosis by scrape preparation and/or frozen section in order to avoid a second surgical intervention for completion thyroidectomy.     

A new BRAF gene mutation detected in a case of a solid variant of papillary thyroid carcinoma

BRAF gene mutations have been frequently detected in papillary thyroid carcinoma (PTC). Moreover, there is a close association between the type of mutation and the PTC histotype: BRAF(V600E) is associated with conventional PTC and with histological variants of PTC displaying a prominent papillary growth pattern, whereas BRAF(K601E) is associated with the follicular variant of PTC. We report the detection of a novel BRAF triplet deletion in a case of PTC displaying a predominantly solid growth pattern. The deletion leads to the replacement of a valine and a lysine by a glutamate in the BRAF activation segment (BRAF(VK600-1E)), thus mimicking partially the 2 BRAF mutations previously described. Our study reinforces the existence of a close relationship between the occurrence of some types of BRAF mutation and some PTC histotypes. The genetic study of more cases of the solid variant of PTC is necessary to find whether there exists a significant association between the occurrence of BRAF(VK600-1E) and such PTC histotype.     

BRAF mutations are associated with some histological types of papillary thyroid carcinoma

Mutations in the BRAF gene have recently been detected in a wide range of neoplastic lesions with a particularly high prevalence in melanoma and papillary thyroid carcinoma (PTC). The hot-spot mutation BRAF(V599E) is frequently detected in PTC (36-69%), in contrast to its absence in other benign or malignant thyroid lesions. In order to unravel whether there is any association between the occurrence of the BRAF mutation and the histological pattern of PTC, in this study a previous series of 50 PTCs was extended to 134 cases, including ten cases of PTC-related entities-hyalinizing trabecular tumour (HTT) and mucoepidermoid carcinoma (MEC). Using PCR/SSCP and sequencing, the BRAF(V599E) mutation was detected in 45 of the 124 PTCs (36%). No mutations were detected in any case of HTT and MEC. BRAF(V599E) was present in 75% of Warthin-like PTCs and 53% of conventional PTCs, whereas no BRAF(V599E) mutations were detected in any of the 32 cases of the follicular variant of PTC. BRAF(V599E) was also detected in 6 of 11 cases of the oncocytic variant of PTC that displayed a papillary or mixed follicular-papillary growth pattern and in none of the four oncocytic PTCs with a follicular growth pattern. A distinct mutation in BRAF (codon K600E) was detected in three cases of the follicular variant of PTC. This study has confirmed the high prevalence of BRAF(V599E) in PTC and has shown that the mutation is almost exclusively seen in PTC with a papillary or mixed follicular-papillary growth pattern, regardless of the cytological features of the neoplastic cells. The results support the existence of an oncocytic variant of PTC that should be separated from the oncocytic variant of follicular carcinoma and suggest that the follicular variant of PTC may be genetically different from conventional PTC.     

Encapsulated follicular variant of papillary thyroid carcinoma with bone metastases.

Although true follicular thyroid carcinoma is known to metastasize via the bloodstream and give rise to bone and lung metastases, such a pattern of spread is rare in papillary thyroid carcinoma. The follicular variant of papillary thyroid carcinoma (FVPTC) is believed to behave in a clinical manner similar to usual or classical papillary cancer and to follow a similar indolent course. There have been a few reports of "aggressive" FVPTC wherein follicular patterned tumors with nuclear features of papillary carcinoma have metastasized hematogenously; these neoplasms have been diffusely invasive or multicentric in the thyroid. We report five cases of FVPTC, which were encapsulated and simulated grossly and microscopically follicular adenomas. In two of these, the primary was discovered after clinical presentation of bone metastases. In three others, bony metastases (without other nonosseous metastases) arose 7 to 17 years after thyroid lobectomy for lesions initially diagnosed as follicular adenoma In retrospect, these three encapsulated lesions had vascular invasion. We wish to bring attention to these innocuous-appearing lesions, which, although sharing nuclear features of papillary cancer, behave clinically in an unexpectedly malignant fashion.     

Differential expression of cytokeratins in follicular variant of papillary carcinoma: an immunohistochemical study and its diagnostic utility.

The follicular variant of papillary carcinoma (FVPTC) is characterized by follicular growth pattern and tumor cells with appropriate nuclear features of papillary carcinoma. However, occasionally these lesions may show focal or multifocal instead of diffuse distribution of nuclear features of papillary carcinoma. Such lesions can be underdiagnosed as benign follicular nodule. Previous studies have shown that cytokeratins, especially 19, are helpful in differentiating papillary carcinoma from other benign and malignant follicular patterned lesions. In this study, we applied monoclonal antibodies to CK5/6/18, CK18, CK10/13, CK20, CK17, and CK19 to paraffin sections of formaldehyde-fixed tissue from 26 cases of FVPTC with multifocal distribution of papillary cancer nuclei, 10 cases of usual variant of papillary carcinoma, 1 case of Warthin's tumor-like papillary carcinoma, and 2 cases of the columnar cell carcinoma. CK19 stained strongly and diffusely all cases of papillary carcinoma. FVPTC cases showed strong staining of the areas with papillary cancer nuclei in all cases and moderate to strong staining in areas of tumor without obvious nuclear features of papillary cancer. Normal thyroid parenchyma adjacent to the tumor nodule showed focal staining in most cases; however, tissue away from the tumor nodule failed to show any staining. All cases of usual type of papillary carcinoma, 2 of columnar cell carcinoma, and 1 Warthin's tumor-like papillary carcinoma showed strong and diffuse staining with CK19 and failed to show any staining of adjacent normal thyroid parenchyma. Similar but less intense staining patterns were seen with CK17 and CK20. The control group, consisting of cases of follicular adenoma, follicular carcinoma, and hyperplastic nodule, showed no staining with CK19. We suggest that if one is using immunohistochemistry to aid in the diagnosis of cases of FVPTC with multifocal distribution of nuclear features of papillary cancer, an antibody panel comprising CKs 17, 19, and 20 may prove helpful. In addition, we hypothesize that the staining of adjacent nontumorous thyroid parenchyma with CK19, seen only in cases of FVPTC, suggests that some factors secreted/produced by this particular tumor may lead to modification in keratin expression of surrounding follicular epithelium.     

HBME‐1 and CD15 immunocytochemistry in the follicular variant of thyroid papillary carcinoma

Papillary carcinoma is the most common thyroid malignancy. As the cytological diagnosis of papillary carcinoma is not difficult in patients with the usual type of lesion, fine‐needle aspiration (FNA) cytology is an effective method for preoperative evaluation. However, this modality is often ineffective in identifying the follicular variant of papillary thyroid carcinoma (FVPTC) due to its similarity to other follicular lesions and the incompleteness of typical nuclear features. Therefore, we investigated the expression of immunocytochemical markers of papillary carcinoma in cytological specimens of FVPTC and evaluated their utilities. The immunoreactivity of HBME‐1 and CD15 was investigated using 50 imprint smear cytological specimens obtained from thyroid lesions, including 13 FVPTC. The sensitivity and specificity of HBME‐1 for FVPTC were 92% and 89%, respectively, while those of CD15 were 23% and 100%, respectively. In conclusion, HBME‐1 is a sensitive marker of papillary carcinoma, including both usual type and FVPTC, in cytological specimens. Therefore, using HBME‐1 immunocytochemistry in FNA cytology will lead to reduction of the incidence of false‐negative diagnoses of FVPTC. Although CD15 is apparently inferior in terms of sensitivity for FVPTC, its excellent specificity will support the definitive diagnosis of thyroid malignancies, including FVPTC, after screening with HBME‐1.     

The p75 neurotrophin receptor is widely expressed in conventional papillary thyroid carcinoma

Papillary thyroid carcinomas (PTCs) are associated with alterations in several proto-oncogenes related with nervous system development and function, such as TrkA and RET, which are commonly rearranged in these carcinomas. The other oncogenic event recently identified in PTC is the BRAF V600E mutation. Because the role of TrkA was not completely elucidated in thyroid cancer ethiopathogenesis, we decided to study the expression of active, phosphorylated TrkA and of its coreceptor p75 neurotrophin receptor (p75 NTR) in a series of 92 PTC (37 lesions of conventional PTC, 28 of follicular variant of PTC [FVPTC], and 27 of other variants of PTC) as well as in 21 samples of normal thyroid and nonneoplastic thyroid lesions used as a controls. We observed neoexpression of p75 NTR in PTC, particularly in conventional PTC and in other variants of PTC displaying a papillary growth pattern, rather than in FVPTC. No immunoexpression of p75 NTR was observed in normal thyroid nor in nonneoplastic thyroid lesions. The cellular localization of p75 NTR immunoexpression was also significantly associated with the growth pattern of PTC, being much more frequently detected in an apical localization in PTC with papillary architecture than in PTC with a follicular or solid growth pattern. This apical localization of p75 NTR was significantly associated with the presence of BRAF V600E. No significant differences were detected between normal thyroid, nonneoplastic lesions, and PTC (or any PTC variant) regarding expression/activation of TrkA, thus suggesting that by itself and in contrast to p75 NTR, TrkA is not altered during PTC development.     

Alterations of the BRAF gene in thyroid tumors

BRAF belongs to the RAF family of protein kinases that are important components of the MAPK signaling pathway mediating cell growth, differentiation and survival. Activating point mutation of the BRAF gene resulting in V600E (previously designated as V599E) is a common event in thyroid papillary carcinoma, being found in approx 40% of this tumor. It has strong association with classical papillary carcinoma and tall cell and possibly Warthin-like variants. This mutation also occurs in thyroid poorly differentiated and anaplastic carcinomas, usually those containing areas of papillary carcinoma. Alterations in the BRAF gene do not overlap with RAS mutations and RET/PTC rearrangement, indicating that activation of one of the effectors of the MAPK pathway is sufficient for papillary thyroid carcinogenesis. Recently, another mechanism of BRAF activation has been identified, which involves chromosome 7q inversion that results in the AKAP9-BRAF fusion. It is rare in sporadic papillary carcinomas and is more common in tumors associated with radiation exposure. Yet another mechanism of BRAF activation may involve copy number gain, which is seen in a significant portion of thyroid follicular tumors of both conventional and oncocytic (Hürthle cell) types.