Lobular and Ductal Breast Cancer: How Do They Differ?

Invasive lobular carcinoma (ILC) is the second most common histologic subtype of breast cancer, after invasive ductal carcinoma (IDC), accounting for 5%–15% of all breast cancers. Several key clinical characteristics have long been appreciated to distinguish ILC from IDC, such as less-clear mammographic visualization and unusual metastatic sites, including serosal surfaces in the abdomen and pelvis.

To better differentiate the clinicopathologic features and outcomes between ILC and IDC, investigators conducted a retrospective cohort study of 3617 ILC patients and 30,045 IDC patients diagnosed between 1990 and 2017 at three large U.S. cancer centers.

Key findings were as follows:

• Compared with IDC patients, ILC patients were more likely to be older (61 vs. 57 years) and to have grade 1 or 2 tumors (88% vs. 60%), higher-stage disease (stage III/IV; 20.7% vs. 10.4%), larger tumor size (T3/4; 14.7% vs. 4.0%), and greater nodal burden (N2/3; 9.9% vs. 5.5%).
• ILC patients were more likely to have ER-positive disease (96% vs. 77%) and PR-positive disease (81% vs. 67%).
• ILC patients were more likely to undergo mastectomy (60% vs. 50%) and less likely to receive radiation (68% vs. 77%).
• Although disease-free survival (DFS) was similar between ILC and IDC patients, ILC patients had significantly worse overall survival (OS); among the subset of ER-positive/HER2-negative patients, DFS and OS were significantly worse for ILC patients, likely reflecting more-frequent late recurrences.