Background: Adolescents and young adults (AYAs; age < 40 years) account for less than 2% of breast cancer patients. Therefore, little is known about the tumor characteristics and care provided to AYA patients. This study sought to describe demographic, tumor, and treatment variables among AYA patients. Methods: The study identified patients ages 15 to 49 years with breast cancer between 2010 and 2015 from the National Cancer Database. Patient and tumor factors were compared using Chi-square tests. Multivariable logistic regression was used to model the effect of age group on treatment while adjusting for confounding variables. Results: The study identified 46,265 AYA patients with stages 0 to 3 breast cancer and compared them with 169,423 breast cancer patients ages 40 to 49 years. A greater proportion of the AYA patients presented with clinical stage 2 or 3 disease than the adult patients 40 to 49 years old (stage 2 disease: 44.3% vs 29.9%, respectively; stage 3 disease: 14.0% vs 7.7%, respectively; both p < 0.001). A greater proportion of the AYA patients had triple-negative breast cancer (TNBC) or human epidermal growth factor receptor 2-positive (HER2+) cancer than the adult patients (TNBC: 21.2% vs 13.8%, respectively; HER2+: 26.0% vs 18.6%, respectively; both p < 0.001). Among the AYA patients, the very young (ages 15–29 years) had more advanced disease and TNBC or HER2+ disease than the older youth (ages 30 to 39 years). The multivariable analysis showed that the AYA patients were more likely to undergo mastectomy (odds ratio [OR] 2.1) and receive chemotherapy (OR 1.9) than patients in their forties (both p < 0.001). Conclusion: A greater proportion of the AYA breast cancer patients had more advanced disease and TNBC and HER2+ disease. The AYA patients had higher rates of mastectomy and use of chemotherapy than the adult breast cancer patients, reflecting that more aggressive therapy is recommended or chosen for women in this age group.
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