Two cases of thyroid cancer in pregnancy treated surgically before delivery

Pregnancy-associated malignant tumors have been reported to occur in approximately 0.1％ of pregnancies in Japan, with thyroid cancer accounting for 3.8％ of these cases.We report two cases of pregnancyassociated advanced thyroid cancer diagnosed during the first trimester of pregnancy.In both cases, disease progression during pregnancy was suspected based on ultrasound and contrast-enhanced CT findings, and surgical intervention was performed during the second trimester prior to delivery.Although thyroid cancer is generally considered a slow-growing malignancy with a favorable prognosis, some cases may demonstrate rapid growth or invasion into adjacent organs, potentially compromising survival and quality of life.Therefore, in cases of pregnancy-associated thyroid cancer, it is essential to determine the optimal treatment approach and timing by considering the biological behavior of the tumor, as well as the health and safety of both the mother and fetus.This report also discusses current trends in domestic and international clinical guidelines.