The term Well Differentiated Thyroid Cancer (WDTC) has been widely used to include Papillary (PTC) and Follicular (FTC) Thyroid cancers in clinical research and guidelines. There are, however, enough differences in their presentation form, surgical approach, and outcomes to abandon the term WDTC.

A unicentric observational study assessing consecutive patients operated for PTC and FTC between August/1993 and March/2022. Insular variant(n=2) and Oncocitic tumors(n=6) were excluded leaving 398 patients for analysis. Survival curves were analyzed by Kaplan-Meier's Log Rank(Mantel-Cox). Propensity Score Matching(PSM) was used to re-assess the findings in comparable groups.

There were differences between PTC (n=285) and FTC (n=44) in age (47±15 vs 55±19 y/o; P=0.008), the proportion of males (17% vs 32%; P=0.001) and tumor diameter (24±15 vs 50±28mm; P=0.0001). Central and/or lateral lymphadenectomy was carried out more frequently in PTC (79% vs 7%; P=0.0001). There were no differences in complications or postoperative stay. RAI was more frequent in FTC (38% vs 57%; P=0.001). The mean follow-up was 9.7±7 years. FTC had more local recurrence (18.9 vs 8.2%; P=0.044) and more M1 (2,2% vs 57,1%; P=0.0001). PTC had better Overall Survival (294±4 vs 244±32 mo.; P=0.04) and better Disease Free Survival (185±18 vs 149±24 mo.; P=0.035). PSM pairing for age and tumor size selected 40 patients per group and did not significantly change these differences.

Differences between PTC and FTC are of such magnitude and span that the term WDTC should be abandoned. Accordingly, research, reports, and clinical guidelines should address these entities separately.