Clinical Approach to Medullary Thyroid Carcinoma in Pregnancy: Experience and Review of the Literature.

Medullary thyroid carcinoma (MTC) during pregnancy is rare and challenging to manage due to its aggressive nature. We describe the successful diagnosis and management of MTC during pregnancy. A 28-year-old woman, who was 5 weeks pregnant, presented with a rapidly growing neck lump and a 10-lb weight loss. Physical examination revealed a left lobe thyroid nodule without palpable lymphadenopathy. Neck ultrasonography revealed a 4.2 × 2.7 × 2.0-cm solid isoechoic left thyroid nodule with calcifications. Calcitonin and carcinoembryonic antigen were elevated. Cytology and Afirma MTC classifier confirmed MTC diagnosis. Genetic testing did not identify mutations within the thyroid cancer panel. With multidisciplinary discussion and shared decision making, the patient underwent total thyroidectomy with neck dissection at 19 weeks' gestation. The effect of pregnancy on MTC is not well studied due to low incidence; thus, there is no consensus on the management of MTC during pregnancy. We detail a case in which surgery was performed in the second trimester with an excellent outcome. Our findings also suggest the reliability of calcitonin and carcinoembryonic antigen as tumor markers during pregnancy. We stress the importance of genetic testing given MTC associations with receptor tyrosine kinase () pathogenic variants and multiple endocrine neoplasia syndromes.