In the WHO classification of breast carcinoma, invasive ductal carcinoma with predominant intraductal component (IDC with PIC) has been defined as carcinomas in which the component of ductal carcinoma in situ amounts to four times more than the invasive element in area. This study was designed to evaluate the clinicopathological significance of IDC with PIC.

Five hundred and seventy nine patients with breast cancer (154 IDC with PIC and 425 with T1 invasive ductal carcinomas) treated with mastectomy or breast conserving surgery between 1989 and 1998 at the Asan Medical Center were divided into two study groups (IDC with PIC and T1 IDC) and compared the clinicopathological characteristics and survival of both groups.

By comparison with the T1 IDC, the IDC with PIC has several distinct features including younger mean age of occurrence (45.3 years vs 48.3 years, P=0.002), larger mean tumor size (3.5 cm vs 1.6 cm, P<0.001), lower incidence of axillary lymph node metastasis (15.7% vs 31.3%, P<0.001) and estrogen receptor positivity (45.7% vs 59.2%, P=0.03), higher incidence of low histologic grade (78.7% vs 61.7%, P=0.002) and cancer detection rate by screening without symptom (21.6% vs 11.5%, P=0.003) or clinical manifestation of nipple discharge (17.3% vs 4.3%, P<0.001) and microcalcification with or without mass on mammography (58.7% vs 30.2%, P<0.001). There were no significant difference in the cumulative 5-year overall and disease-free survival rates (93.1% vs 90.1%, P=0.78; 89.5% vs 86%, P=0.23). In the IDC with PIC group, tumors larger than 2 cm in size were more frequently metastasized to axillary lymph nodes than tumors smaller than 2 cm, but this finding was not significant (P=0.07).

Invasive ductal carcinoma with predominant intraductal component showed less invasive and more low-grade malignant characteristics than T1 invasive ductal carcinoma. Survival was not statistically different.