[Clinicopathologic and molecular features of cribriform morular variant of papillary thyroid carcinoma]

Objective: To investigate the clinicopathologic and molecular features of the rare cribriform morular variant of papillary thyroid carcinoma (CMV-PTC). Methods: The clinicopathologic data of 10 patients with CMV-PTC were retrospectively reviewed. Immunohistochemical (IHC) staining was done using LSAB method. DNA sequencing for APC were applied using Sanger method. BRAF V600E mutation was examined using ARMS method. The cytological, morphological, IHC and molecular features were analyzed. Results: All patients were female at an average age of 27 years old. The tumors were mostly located in the right lobe of thyroid. Fine needle aspiration cytology was performed in three patients; two were diagnosed as suspicious for PTC and one as PTC. Nine tumors presented as solitary nodule and two as multiple nodules in both lobes. Infiltration was demonstrated in three cases. The average size was 2.6 cm. The neoplastic cells were arranged in papillary, cribriform, solid and glandular patterns, with rare or without colloid inside the lumen. The number of morula varied, ranging from zero to many. The neoplastic cells were variably enlarged, showing round, oval or spindle shape. Nuclear irregularity was identified as irregular membrane, nuclear grooves or pseudoinclusion, but no typical ground glass feature. Peculiar nuclear clearing could be observed in the morular cells. IHC staining showed the neoplastic cells were negative for thyroglobulin and p63, but positive for TTF1, cytokeratin 19 and estrogen receptor. Diffuse staining with cytokeratin was seen in the neoplastic cells and the morula. Specific cytoplasmic and nuclear staining of β-catenin was seen in the neoplastic cells but not the morula. Ki-67 proliferation index was 1%-30%. No recurrence or metastasis was observed. One patient was demonstrated to harbor both somatic and germline mutations of the APC gene, who was found to have adenomatous polyposis and her mother died of colonic carcinoma. No BRAF V600E mutation was detected. Conclusions: CMV-PTC is rare and shows atypical cytological and clinicopathological features, and it is easily misdiagnosed.TG, TTF1, ER and β-catenin are specific IHC markers for CMV-PTC. The morula is negative for cytokeratin 19, in contrast to squamous metaplasia. Although CMV-PTC has indolent clinical behavior, a definite diagnosis is necessary to rule out the possibility of APC gene mutation and related extra-thyroidal neoplasm, such as FAP and Gardner syndrome.

LEF-1 is a Sensitive Marker of Cribriform Morular Variant of Papillary Thyroid Carcinoma

Cribriform morular variant of PTC (CMV-PTC) frequently shows activation of the CTNNB1/Wnt pathway with nuclear accumulation of beta catenin. The utility of LEF-1, also in the CTNNB1/WNT pathway, in the diagnosis of CMV-PTC has not been previously studied. LEF-1 immunohistochemistry was performed on seven CMV-PTC, 52 benign cases and 101 malignant thyroid neoplasms. LEF-1 was scored by stain intensity (0 = no nuclear stain, 1 = weak nuclear stain, less than lymphocyte and 2 = strong nuclear stain, intense as lymphocyte) and percentage of positive cells at each intensity, for a maximum total score of 200. Sensitivity and specificity of LEF-1 stain for all cases and to differentiate between regular PTC and CMV-PTC was also calculated. Six of the seven CMV-PTCs showed ≥ 30% strong (2+) nuclear LEF-1 staining and a total score over 100. Beta catenin also showed strong and diffuse nuclear staining in these cases. One CMV-PTC was negative for both LEF-1 and beta catenin and did not have a history of FAP. All control PTC cases uniformly lacked LEF-1 staining at 2+ intensity. LEF-1 had a sensitivity of 86% and specificity of 98% for the diagnosis of CMV-PTC. LEF-1 is highly sensitive and specific marker for CMV-PTC, especially when used in the setting of a PTC neoplasm. The pattern of staining is important with ≥ 30% of cells showing strong 2+ nuclear staining having the highest combined sensitivity and specificity.