The Japanese Thyroid Association Reporting System of Thyroid Aspiration Cytology and Experience from A High-volume Center, Especially in Indeterminate Category

Background: In 2013, the Japan Thyroid Association (JTA) published thyroid nodule management guidelines, and the new cytology reporting system in the guidelines is based on the Ito Hospital system. The key feature of the system is that the indeterminate category is subdivided into category A and category B. Suspected follicular lesions are classified in category A, and it is subdivided into: A-1 (favor benign), A-2 (borderline), and A-3 (favor malignant). Lesions suspected of being other than a follicular lesion are classified in category B. Patients and Methods: The 6891 patients (7442 nodules) who underwent thyroid ABC between January and December 2013 and subsequently underwent surgery were adopted as the subjects of this study. We reassessed the ABC by the JTA reporting system and made comparisons with the histology. When we classified a sample to category A, we scored the amount of cells collected by assigning 1 point when the volume was small, 2 points when intermediate, and 3 points when large; we scored degree of nuclear overlapping by assigning 1 point when mild, 2 points when moderate, and 3 points when high; and we scored degree of nuclear atypia by assigning 1 point when mild, 2 points when moderate, and 3 points when high; we then calculated the total score. When the total score was 3, 4, or 5, the lesion was classified in category A-1, when 6 or 7, it was classified in category A-2, and when 8 or 9, it was classified in category A-3. Results: The 7442 nodules consisted of 140 classified as inadequate (1.9%), 5365 (72.1%) as normal or benign, and 486 (6.5%) as indeterminate, and 400 (5.4%) of the nodules were classified in category A, i.e., follicular tumor suspected. Of the 400 nodules classified in category A, 201 (2.7%) were classified as A-1, 93 (1.2%) as A-2, and 34 (0.5%) as A-3, and 72 nodules (1.0%) were suspected of being oxyphilic cell tumors. Category B consisted of 86 nodules (1.2%); 189 nodules (2.5%) were suspected of being malignant, and 1262 nodules (17.0%) were malignant. Among the cases in which the lesions had been classified as A-1, the histological diagnosis was adenomatous goiter in 23 cases (44.2%), follicular adenoma in 23 cases (44.2%), follicular carcinoma, minimally invasive type in 6 cases (11.5%), and follicular carcinoma, widely invasive type in 0 cases (0%). In category A-2 the histological diagnosis was adenomatous goiter in 7 cases (24.1%), follicular adenoma in 11 cases (37.9%), follicular carcinoma, minimally invasive type in 7 cases (24.1%), and follicular carcinoma, widely invasive type in 14 cases (48.3%). In category A-3 the histological diagnosis was adenomatous goiter in 0 cases (0%), follicular adenoma in 2 cases (18.2%), follicular carcinoma, minimally invasive type in 6 cases (54.5%), and follicular carcinoma, widely invasive type in 3 cases (27.3%). There were no cases of papillary carcinoma or medullary carcinoma. The malignancy rates were: A-1, 11.5%; A-2, 53.8%; and A-3, 81.8%. Conclusion: When we tried evaluating the cytology of follicular tumors by the scoring system we established based on the JTA system in the present study, clear differences were obtained between the rates of follicular carcinoma in categories A-1, A-2, and A-3. It is impossible to avoid the occurrence of differences in the results of evaluations by pathologists even in the same case. It is important for surgeons and pathologists in each institution to reach a sufficient consensus in regard to the cytological category and surgical indications.