Incidence and survival outcomes of breast cancer subtypes in the United States.

e13184 Background: While the overall incidence of breast cancer (BC) in the US has been increasing, the epidemiology and outcomes of specific histological subtypes of BC remain insufficiently studied. This study utilized the Surveillance, Epidemiology, and End Results (SEER) database to evaluate the incidence, trends, and survival outcomes of different BC histologic subtypes. Methods: Data on female BC cases diagnosed between 2000 and 2021, including the subtypes: infiltrating ductal carcinoma, lobular carcinoma, metaplastic carcinoma, mucinous adenocarcinoma, papillary carcinoma, tubular adenocarcinoma, adenoid cystic carcinoma, apocrine adenocarcinoma, cribriform carcinoma, and medullary carcinoma were extracted from the SEER database. Age-adjusted incidence rates (AAIRs) and annual percent changes (APCs) were calculated using SEER*Stat v.8.4.4. The Cox proportional hazard model assessed survival outcomes adjusting for treatments including surgery, chemotherapy, and radiation using R v 4.3.2. software. Results: A total of 897,715 BC cases were identified: 765,048 infiltrating ductal carcinoma (85.1%), 90,951 lobular carcinoma (10.1%), 20,916 mucinous adenocarcinoma (2.3%), 7,905 tubular adenocarcinoma (0.9%), 3,901 metaplastic carcinoma (0.4%), 3,168 medullary carcinoma (0.4%), 2,251 apocrine adenocarcinoma (0.3%), 1,929 cribriform carcinoma (0.2%), 1803 papillary carcinoma (0.2%), and 813 adenoid cystic carcinoma (0.1%). The AAIR increased most significantly in metaplastic carcinoma (APC 3.54%, 95% CI 2.41–4.69) and lobular carcinoma (APC 1.58%, 95% CI 1.20–1.96. In contrast, the AAIR decreased the most in medullary carcinoma (APC -10.72%, 95% CI -12.18 to -9.23), followed by tubular adenocarcinoma (APC: -7.88%, 95% CI: -8.85 to -6.9). Multivariable analysis found metaplastic carcinoma had the highest mortality risk compared to infiltrating ductal carcinoma (HR 2.01, 95% CI 1.91–2.11, p < 0.001) in the table. Conclusions: Metaplastic lobular carcinoma demonstrated the highest trend in annual increase in incidence and mortality, underscoring the urgent need for targeted interventions and further research in this subgroup. Additionally, while mucinous adenocarcinoma has been reported to have better survival outcomes in previous studies, our findings indicate a higher mortality risk compared to infiltrating ductal carcinoma, warranting further exploration. Multivariable analysis survival outcome of breast cancer subtypes. Subtypes aHR 95% confidence interval P value Infiltrating ductal carcinoma 1.00 (reference) Metaplastic carcinoma 2.01 1.91-2.11 <0.001 Apocrine adenocarcinoma 1.28 1.20-1.37 <0.001 Mucinous adenocarcinoma 1.15 1.12-1.17 <0.001 Lobular carcinoma 1.10 1.08-1.11 <0.001 Cribriform carcinoma 0.84 0.77-0.92 <0.001 Adenoid cystic carcinoma 0.77 0.67-0.90 <0.001 Medullary carcinoma 0.74 0.69-0.79 <0.001 Tubular carcinoma 0.73 0.70-0.76 <0.001