Importance of Regular Follow-Up Examination during Active Surveillance: a Case of Anaplastic Transformation of Papillary Thyroid Microcarcinoma

ABSTRACT

Because papillary thyroid carcinoma (PTC) is indolent and has an excellent prognosis, active surveillance, without immediate surgery, can be considered for small PTC. However, rarely, PTC can transform to anaplastic thyroid carcinoma (ATC), over a period of 5-20 years. We report 73-year-old man with rapid anaplastic transformation of a PTC. He was diagnosed with colorectal cancer, and a 1-cm-sized thyroid nodule was found incidentally and confirmed as PTC on fine-needle aspiration. He underwent transanal excision and chemotherapy for colorectal cancer. However, he was not concerned about the PTC, and no follow-up examination was performed. After 37 months, he suddenly noticed an enlarging neck mass, which was diagnosed as an ATC. Despite total thyroidectomy, locally advanced recurrence with lung metastasis developed, and he eventually died. Although PTC is indolent and progresses slowly in elderly people, it can transform to ATC. Therefore, during active surveillance in the elderly, follow-up examinations should be performed regularly.