Background:To present the clinical picture and outcome of poorly differentiated insular-type thyroid carcinoma (ITC) compared with papillary thyroid carcinoma (PTC) in a Mexican population in order to demonstrate their different biological behavior.Material/Methods: Retrospective, transversal study comparing ITC (G1) with PTC (G2). Assessed variables were: age, gender, size of tumor, previous history of thyroid disease, and outcome. The recurrence/death risk was established according to the MACIS, De GROOT, and AMES classifications. Statistical analysis was made by means of central tendency measures, the Kaplan-Meier method, Cox-Mantel’s log-rank, Student’s t, and chi-square tests.Results: Both groups were classified based on a high or low risk for thyroid neoplasms. G1 had 13 patients, tumor volume was 78 cm3, 7 cases presented metastases at the time of admittance, five had antecedents of goiter. Average follow-up time was 23 months. G2 had seventy-one patients, tumor volume was 42 cm3, and follow-up time of 44 months. Kaplan-Meier revealed a lower survival in Group 1 than Group 2, statistically significant by the Cox-Mantel log-rank test. A significant statistical difference existed regarding survival and the presence of metastases: G1 (61%) and G2 (53.8%). No statistical difference was found between tumor size.Conclusions: ITC is more aggressive than PTC. It occurs in the 6th decade of life, with antecedents of long-standing goiter, and has a high recurrence, metastasis and mortality frequency.

Keywords: Carcinoma - diagnosis, Carcinoma - pathology, Carcinoma, Papillary - diagnosis, Recurrence, Sex Factors, Thyroid Gland - metabolism, Thyroid Neoplasms - diagnosis, Thyroid Neoplasms - pathology, Time Factors, Carcinoma - pathology, Carcinoma, Papillary - diagnosis, Recurrence, Sex Factors, Thyroid Gland - metabolism, Thyroid Neoplasms - pathology, Time Factors