Medullary breast cancer is a predominantly triple-negative breast cancer - histopathological analysis and comparison with invasive ductal breast cancer

Introduction: Medullary breast cancer (MdBC) is an uncommon type of breast cancer representing 1-7% of all cases. It is characterized by the occurrence of many histopathological features associated with a high grade of malignancy. Material and methods: Twelve MdBCs chosen from a group of 1,122 women suffering from invasive breast cancer were analyzed. Histopathological examination and analysis of a basic molecular profile, i.e. estrogen (ER), progesterone (PR) and HER2 receptor expression, and their comparison with invasive ductal breast cancer (IDC), were performed. Results: MdBC accounted for 1.07% of all analyzed invasive breast cancer patients. All patients were female, with an average age of 58.54 years. The MdBC group exhibited a larger median tumor diameter (2.05 vs. 1.89 cm), although >= T2 tumors comprised 42% vs. 51% for IDCs. Women without regional lymph node involvement (pN0) (83%) formed the largest group. There was a statistically significant difference in the presence of nodal involvement between the studied groups (p < 0.001). Based on the histological grade of malignancy, the majority of MdBC comprised grade II tumors (G2) (93%). In general, MdBC showed statistically higher histologic grade (G1-G3) than IDC (p = 0.003). The 5-year overall survival rate of MdBC patients was 91%. Most MdBCs (92%) were triple-negative, whereas the remaining 8% were HER2 positive. Conclusions: MdBC presented at a younger age than IDC, had a higher histological grade, larger median size and less frequent regional lymph node involvement. Most MdBCs were triple-negative, whereas IDCs were predominantly luminal. Despite numerous aggressive pathological features of MdBC, its clinical outcome and overall prognosis are favorable.

Automated summary

Medullary breast cancer (MdBC) is a rare and highly malignant type of breast cancer. MdBC patients tend to be younger, have higher histological grade, larger tumor size, and less frequent lymph node involvement. Most MdBCs are triple-negative (not expressing estrogen receptor, progesterone receptor, and HER2 receptor), while IDCs are predominantly luminal (expressing estrogen receptor and/or progesterone receptor).