Are the pure in situ breast ductal carcinomas and those associated with invasive carcinoma the same?

It has been reported that pure ductal carcinoma in situ of the breast has morphologic differences from the in situ component of the invasive ductal carcinoma, as well estrogen and progesterone receptors expression according to their cytokeratin expression. However, there is no data comparing other tumor markers without using the cytokeratin expression. The objective of this study is to compare the expression of estrogen receptor (ER) and progesterone receptor (PR), HER-2/neu, p53, and Ki67 between pure ductal in situ carcinoma (pDCIS) and the in situ component of the invasive ductal carcinoma (DCIS + IDC) of the breast, and the in situ component to the invasive component of the same tumor (DCIS + IDC). The immunohistochemistry expression of the tumor markers was performed in 45 cases of pDCIS and DCIS + IDC, yielding a total of 90 cases. Statistical analysis was carried out using Fisher exact test, having a P < 0.05, and Kappa index (kappa) to assess intratumoral concordance. In DCIS + IDC, the in situ and invasive components did not show a significant difference and Kappa index (kappa) was high (0.7-1) for positive and negative expression. ER and PR were significantly different between the pDCIS and DCIS + IDC (ER: 86.7 vs. 66.7% P = 0.04; PR: 80% vs. 55.6% P = 0.02). These findings suggest that in situ component of DCIS + IDC and pDCIS are distinct conditions.