Comparison of secondary and primary thyroid cancer in adolescents and young adults

BACKGROUND Thyroid cancer is one of the 5 most common malignancies in adolescent and young adult (AYA) patients (ages 15-39 years) and may develop de novo or in patients previously treated for cancer. This study compared the tumor characteristics, treatment, and overall survival (OS) of secondary malignant neoplasm (SMN) versus primary thyroid cancer in AYA patients. METHODS All cases of AYA thyroid cancer contained in the 1998 to 2010 American College of Surgeons National Cancer Database were divided into 2 cohorts according to primary or secondary occurrence. Comparisons using appropriate statistical methods were performed. RESULTS Of 41,062 cases, 1349 (3.3%) had experienced a prior malignancy. Compared with cases of primary thyroid cancer, SMNs were more likely multifocal (odds ratio [OR] = 1.173, 95% confidence interval [CI] = 1.049-1.313) microcarcinomas < 1 cm (OR = 1.496, 95% CI = 1.327-1.687) with tall/columnar cells (OR = 2.187, 95% CI = 0.534-0.692), of white race (OR = 2.643, 95% CI = 1.310-5.331) and age 35-39 years (OR = 1.239, 95% CI = 1.093-1.404) and less likely female (OR = 0.608, 95% CI = 0.534-0.692), Hispanic (OR = 0.779, 95% CI = 0.642-0.946) age 15-19 years (OR = 0.624, 95% CI = 0.510-0.763) or 25-29 years (OR = 0.711, 95% CI = 0.604-0.837), or less likely > 4 cm in size (OR = 0.610, 95% CI = 0.493-0.758). There was a 6.63-fold (95% CI = 4.97-8.86, P < .001) relative risk of death for secondary versus primary thyroid cancers after adjusting for demographic, tumor, and thyroid treatment factors. Only Hispanic origin, tall/columnar cell histology, and distant metastases decreased OS for SMNs. CONCLUSIONS AYAs who develop thyroid cancer as a SMN have a significantly decreased OS compared to AYAs with primary thyroid cancer. Multiple demographic and tumor differences exist between these 2 cohorts. Whether the outcome disparity results from previous cancer treatment or differences in biology, environment, or access to care are areas needing further investigation.