Proposal for including risk of malignancy and clinical management in the Japanese system for reporting thyroid cytopathology - A multi-institutional study.

Objective: The Japanese System for Reporting Thyroid Cytopathology (JSRTC) does not include the risks of malignancies (ROMs) or recommended clinical management. This multi-institutional study aimed to determine the frequency, re-aspiration rate, resection rate, ROM, and clinical management options in seven different categories.

Material and methods: For 15,495 cases of thyroid fine-needle aspiration performed at seven Japanese institutions without molecular testing, the frequency, re-aspiration rate, resection rate, ROM, and clinical management options of each diagnostic category were examined. The categorization was based on JSRTC, and cases were subdivided into those with nuclear atypia and other subtypes for undetermined significance.

Results: Re-aspiration of unsatisfactory and undermined significance diagnostic categories was mainly performed for cases of suspected malignancy on ultrasound. The median re-aspiration rate of cyst fluid nodules was 4.9%, which was significantly different from that (17.8%) of unsatisfactory cases (P < 0.05). The resected ROMs for nodules that were suspicious for malignancy and malignant were 94.2% and 99.6%, respectively. The low resection rates of nodules that were suspicious for malignancy (77.8%) and malignant (70.8%) could be attributed to active surveillance for low-risk papillary microcarcinoma. The overall ROMs of unsatisfactory, cyst fluid, benign, undetermined significance, and follicular neoplasms were 4.5%, 0.4%, 0.7%, 16.7%, and 11.4%, respectively. In the subtype of undetermined significance, the overall ROM of nuclear atypia (27.6%) was higher than that of the others (6.7%).

Conclusion: Overall, this study determines the frequency, ROM, and recommended clinical management for thyroid cytopathology in Japan. These results were different from those proposed by the Bethesda System for Reporting Thyroid Cytopathology. In the future, our results will be helpful in the revision of JSRTC and will contribute to improving the outcomes among Japanese patients with thyroid nodules.