Difference in characteristics and outcomes between medullary breast carcinoma and invasive ductal carcinoma: a population based study from SEER 18 database

Medullary breast carcinoma (MBC) is a unique histological subtype of breast cancer. Our study was designed to identify difference in characteristics and outcomes between MBC and invasive ductal carcinoma (IDC), and further confirm the prognostic factors of MBC. Utilizing Surveillance, Epidemiology, and End Results (SEER), we identified 84,764 eligible patients, including 309 MBC and 84,455 IDC. Compared with the IDC group, the MBC group was associated with younger age at diagnosis, higher grade, more advanced stage, larger tumor size, and higher proportion of triple-negative breast cancer (TNBC). Kaplan-Meier analysis and univariate Cox proportional hazard regression model showed that patients with IDC had significantly better breast cancer-specific survival (BCSS) compared to MBC, but they had similar overall survival (OS). However, MBC histology was no longer a surrogate for worse BCSS or OS after 1:1 matching by age, American Joint Committee on Cancer (AJCC) stage, grade and breast subtype. In addition, it was exposed that not married status, high grade, large tumor size, positive nodal status, the subtype of TNBC and no receipt of radiation therapy were significantly associated with poor BCSS and OS. In conclusion, MBC demonstrated more aggressive behavior but similar outcomes compared to IDC, which may be determined by prognostic factors such as breast subtype. These results not only confer deeper insight into MBC but contribute to individualized and tailored therapy, and thereby may improve clinical management and outcomes.