Pathological features of invasive ductal carcinoma of the breast according to expression of progesterone receptor

Abstract

Background: Loss of PR expression in breast cancer is associated with older patients, larger tumors, higher grade tumors and tumors over-expressing HER2. We previously reported that loss of PR expression predicts higher Recurrence Scores (RS) of the 21-gene assay (Oncotype DX) and higher risk for bone metastasis. Recently, a 20% or less PR expression was proposed to separate Luminal B from Luminal A subtype of breast cancer. Here we intend to study the relationship between the different levels of PR expression and various pathologic features in invasive ductal carcinoma (IDC) of the breast.<br>Design: 3573 cases of primary IDC of the breast from our institution diagnosed between 1997 and 2013 and had an immunohistochemical (IHC) score for ER and PR in exact percentage were included in the study. The clinicopathological features (age, size, nodal status, lymphovascular invasion (LVI) status, histological grade (HG), and expression of ER, PR, HER2 and Ki-67) were collected for each case. The relationships between the levels of PR expression (<1%, 1-20%, 21-50%, 51-70% and 71-100%) and these pathologic features were analyzed.<br>Results: Among the 3573 cases, the mean age was 59.9 years, the mean tumor size was 2.05cm, 31% had nodal metastasis, 18% had LVI, 85%, 78% and 12.4% were positive for ER, PR and HER2 respectively. 53% showed Ki67 labeling equal or greater to 15%. Significant differences in LVI, HG and ER expression were observed between the PR<1% and PR 1-20% subgroups, and the PR 1-20% and PR 21-50% subgroups, with higher incidence of LVI, higher HG and lower ER expression associated with the subgroups having lower PR expression. These differences were not observed between the subgroups of PR 21-50% and 51-70%, or PR 51-70% and PR 71-100%. In ER positive tumors, significant difference was noted for all pathologic features studied (tumor size, nodal status, LVI status, histological grade, and expression HER2 and Ki67) except for patient age. Similar differences were also identified for these subgroups in HER2 negative tumors, but not in HER2 positive tumors.<br>Conclusions: The difference observed in between PR<1% and PR 1-20% and between PR1-20% and PR 21-50% suggests that the cut offs of 1% and 20% for PR may be biologically important for IDC. The different levels of PR expression may play critical roles in ER positive and HER2 negative breast cancer.