[Anaplastic thyroid carcinoma: Importance of early diagnosis and treatment].

Anaplastic thyroid cancer (ATC) is a rare and extremely aggressive malignant tumor that accounts for approximately 2% of thyroid carcinomas. Fifteen to 50% of patients present extensive local regional invasion and distant metastasis at the time of diagnosis; therefore, ATC is classified as Stage IV according to the 8th edition of the American Joint Committee on Cancer (AJCC) Cancer Staging Manual. Overall survival is approximately 5 months, and the 1-year survival rate is around 20%. However, in recent years, there has been an improvement in this rate thanks to early diagnosis, rapid therapeutic intervention, the advent of molecular testing and the pharmacological options. Two clinical cases with unusual evolution are presented, who underwent initial treatment with total thyroidectomy, adjuvant radiotherapy and concurrent chemotherapy both free of disease after 66 and 42 months of follow up.