Aim Invasive lobular carcinoma (ILC) and invasive ductal carcinoma (IDC) of the breast are distinct morphological entities with different biological features and clinical behaviour. In the present study, the authors compare the axillary-lymph-node (ALN) status of patients with grade-matched ILC (no=426) and IDC (no=820). The pattern of nodal metastatic deposits (nodular, sinusoidal and diffuse) and the proportion of involved nodes were also analysed in a selected group of 246 tumours, which were associated with a single positive ALN.

Results Compared with grade-matched IDC, ILC was associated with a higher nodal stage (13.1% vs 4.5% of ILC and IDC were stage 3), higher absolute number of positive nodes and higher ratio of positive nodes (0.46±0.30 and 0.33±0.23 in ILC and IDC respectively). These differences were maintained in the different size subgroups. The most common metastatic morphological pattern was nodular in both types of carcinomas. A sinusoidal pattern was more frequent in IDC, and the diffuse pattern was more frequent in ILC. Despite these differences, ILC and grade-matched IDC exhibited similar rates of regional recurrences (RR) and breast-cancer survival.

Conclusion This study provides clinical evidence which further demonstrates that ILC and IDC are biologically distinct entities with different lymph-node involvement patterns and ILC having a tendency to metastasise to more nodes than IDC. However, this difference was not associated with a significant impact on patient outcome.