MON-561 Medullary Thyroid Cancer in a Single Institution: Factors Associated With Biochemical Failure

Abstract

Background: Medullary thyroid carcinoma (MTC) is a rare thyroid cancer with a disproportionate high mortality and can be sporadic or familial. Surgery is the only potentially curative treatment. Our aim was to access demographic, clinical and pathological characteristics of MTC patients associated with biochemical failure after surgery. Methods: Retrospective observational study of patients with MTC diagnosed between 1984 and 2018 and followed-up in our institution. Results: We evaluated 76 individuals with MTC, 27.6% with hereditary MTC, 69.7% female, median of age 49 years-old (IQR 33.50-60.00). The median of preoperative calcitonin levels was 1121 pg/mL (IQR 445-4383), being ≥500 pg/mL in 72.3%. Preoperative calcitonin levels, when performed, had a sensitivity of 97.9%. According to TNM staging (AJCC 8th ed.), 35.9% were in stage I, 15.6% in stage II, 1.6% in stage III and 46.9% in stage IV. One patient had poor functional status, contraindicating surgery. A total of 75 patients were submitted to thyroidectomy (or completion thyroidectomy when indicated) with lymph node dissection at our institution (n=50) or an outside one (n=25). Biochemical cure (BC) was achieved in 48 (64%) patients after surgery; of these, 7 (14.58%) relapsed. BC was 95.7% in stage II, 100% in stages II/III and 24.1% in stage IV (p<0.001). Biochemical failure occurred in 36% of patients, all of them with preoperative calcitonin levels ≥500 pg/mL (p<0.001). There were no significant differences in sex, age, presence of germline RET mutation and results of fine-needle aspiration cytology between groups. Regarding histological features, patients with biochemical failure had higher tumor size (2.5 cm vs. 1.9 cm, p=0.025), multifocality (66.7% vs. 37.5%, p=0.024), vascular invasion (76.5% vs. 43.8%, p=0.028), perineural invasion (23.4 % vs. 0%, p=0.024), capsular invasion (82.4% vs. 12.1%, p<0.001), extrathyroidal extension (57.9% vs. 7.9%, p<0.001), surgical margin positivity (57.9% vs. 7.9%, p<0.001) and lymph node positivity (100% vs. 33.3%, p<0.001). Preoperative calcitonin levels (OR per increments of 500 pg/mL=1.183; p=0.012), tumor size in cm (OR=2.093; p=0.003), multifocality (OR=2.769; p=0.049), vascular invasion (OR=4.250; p=0.024), capsular invasion (OR=27.000; p<0.001), extrathyroidal extension (OR=85.000; p<0.001), surgical margins positivity (OR=17.455; p=0.001) and lymph nodes positivity (OR=62.500; p<0.001) were predictors of biochemical failure. The 5-year survival rate was higher in the BC group (91.7% vs. 74.1%; p=0.049). Conclusions: Several tumor histological characteristics were the best predictors for biochemical failure and preoperative calcitonin level was the only significant predictor performed before surgery. Demographic data, RET mutation and cytology were not associated with BC. These findings highlight that early detection is important to achieve BC in MTC.