[Significance of micropapillary histopathological subtype of thyroid carcinoma]

Objective: To study the clinical and pathologic factors of papillary thyroid microcarcinoma (PTMC) and its significance as a histopathologic subtype of papillary thyroid carcinoma (PTC). Methods: A retrospective study of 719 patients with non-high-risk PTMC who underwent surgery for the first time in the Peking University People's Hospital from January 2007 to June 2019 was conducted, the relationship between clinicopathologic factors and lymph node metastasis, and the expression of four tumor markers CK19, HMBE1, Galectin-3 and CD56 by immunohistochemistry were evaluated. Some comparisons were made with PTC. Results: The peak patients' age was 40-49 years for both non-high-risk PTMC and PTC; the lymph node metastasis rate was higher in the 30-39 years age group than the 50-59 years age group (P<0.05); the lymph nodes metastasis rate was significantly higher for multiple lesions than for single lesion (P<0.05). Lymph node metastasis rate of PTMC with capsular invasion was significantly higher than those without (P<0.05). There was no significant correlation between lymph node metastasis of PTMC and patients' gender, tumor location, tumor size, and lymphocytic thyroiditis. The expression rates of CK19, HMBE1 and Galectin-3 both in PTMC and PTC were 100%, and the expression rates of CD56 were 25.6% (85/332) and 20.0% (70/350) respectively. Conclusion: As the main pathologic subtype of PTC, a variety of clinicopathologic factors of PTMC are related to lymph node metastasis, and it is highly recommended to pay close attention to PTMC. The expression of tumor marker CD56 alone cannot be used as a basis to exclude PTMC and PTC.