Does every classical type of well-differentiated thyroid cancer have excellent prognosis? A case series and literature review

The classical type of well-differentiated thyroid cancer (WDTC) is the most common endocrine tumor with generally excellent prognosis. WDTC of the WHO stage 1 classification metastasizing to the vertebral column is not often seen for this neoplasm. Here, I present a case series of 14 individuals with aggressive classical type of WDTC. To identify the most aggressive cases of classical type WDTC, I reviewed the medical records of 4,327 patients consecutively admitted and surgically treated in a single institution for thyroid pathology in the years 2008-2016. Demographic, pathological and outcome data were collected and reviewed. During the study period, 14 (4.02%) patients with aggressive forms of the classical type of WDTC were reviewed: 10 (2.87%) cases with papillary thyroid cancer (PTC) and 4 (1.14%) with follicular thyroid cancer (FTC). The median age at diagnosis was 61 years (31-84 years). Aggressive features such as extrathyroid extension 11/14 (78.57%), positive surgical margins 11/14 (78,57%), lymph node metastases 7/14 (50%), multifocality 6/14 (42.85%), regional tissue infiltration 11/14 (78.57%) and distant metastases 4/14 (28.57%) were observed. Long-term follow-up (median 40 months) demonstrated a high rate of locoregional recurrence in 12/14 (85.71%) individuals. Pulmonary and other distant metastases were observed in 4/14 (28.57%) patients, with mortality in 3/14 (21.42%) individuals. In patients with classical type of WDTC characterized by excellent prognosis, extremely aggressive entities might be observed, making WDTC in some cases an unpredictable tumor.