OP51 – Risk factors for biochemical and structural incomplete response in a series of 1840 thyroid microcarcinomas

      Ferraz,  Carolina1; Simões, Vivian1; Faro, Fernanda1; Cabral, Cristal1; Scalissi, Nilza1; Cury, Adriano1; Marone Marilia2; Padovani Rosalia1,2 1 Endocrinology Unit, Internal Medicine Department of Santa Casa de Sao Paulo, School of Medicine Sciences, Sao Paulo, Brazil 2 Nuclear Medicine Service of Santa Casa de Sao Paulo, School of Medicine Sciences, Sao Paulo, Brazil   Background: Thyroid microcarcinoma (TMC) is a differentiated thyroid carcinoma (DTC) classified as low-risk of recurrence and the treatment proposed is lobectomy or even active surveillance1,2. However, some patients show a higher risk of disease recurrence1. Some factors are described as possible indicators for a worse outcome. Objective: identify possible risk factors associated with TMC incomplete response3,4. Methods: A retrospective study of 1840 patients were stratified according to persistence/recurrence risk and response to initial therapy. Age, gender, size of the tumor, histological variants, multifocality, vascular invasion, extrathyroidal extension, lymph node and distant metastasis were evaluated. Results: From 1840 patients, 89.8% were women, mean age 46.8±12.1years. 96% were papillary carcinomas. 25.3% had multifocal disease, 4.7% vascular invasion, 18.5% extrathyroidal extension, 10.4% lymph node metastasis and 0.1% had distant metastasis. Regarding risk of recurrence, 79.7% were low risk and 2.3% high risk. After reclassifying patients, 63.5% had an excellent, 15.1% an indeterminate, 8.5% biochemical incomplete, and 12.6% showed structural incomplete response. Multivariate analysis demonstrated that multifocality (OR:1.53) and lymph node metastasis at diagnosis (OR:2.11) were independently associated with incomplete response. Radioiodine therapy did not influence the type of response in patients with multicentricity. Discussion/Conclusion: Although patients with TMC are considered low risk and generally evolve well1,2, a special group of patients, showing multifocality and lymph node metastasis at diagnosis, can evolve with disease recurrence and thereby could benefit from a surgical treatment, however without benefit with additional radioiodine treatment.   References:
    1. Ito Y, Miyauchi A, Kihara M, Higashiyama T, Kobayashi K, Miya A 2014 Patient age is significantly related to the progression of papillary microcarcinoma of the thyroid under observation. Thyroid 24:27–34.
    2. Haugen BR, et al. The American Thyroid Association Guidelines Task Force on Thyroid Nodules and Differentiated Thyroid Cancer. Thyroid, 2016. Volume 26, Number 1.
    3. Ito Y, Fukushima M, Kihara M, et al. Investigation of the prognosis of patients with papillary thyroid carcinoma by tumor size. Endocr J 2012; 457-464
    4. Allo MD, Christianson W, KoivunenD . Not all ‘‘occult’’ papillary carcinomas are ‘‘minimal’’. Surgery.1998; 971-97


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