Incidence, Clinicopathologic Features, and Follow-up Results of Invasive Ductal Carcinoma With Lobular-Like Growth Pattern

BACKGROUND: Invasive ductal carcinoma (IDC) and invasive lobular carcinoma (ILC) are the two most common breast cancers. A subset of tumors with discohesive, lobular-like growth but retained membranous E-cadherin expression-termed invasive ductal carcinoma with lobular-like growth pattern (IDC-LL)-is increasingly recognized, yet its clinicopathologic and prognostic significance remain unclear. MATERIALS AND METHODS: We retrospectively reviewed 2,413 invasive breast carcinomas (1,872 IDC, 230 IDC-LL, 311 ILC) diagnosed between 2016 and 2022. Clinicopathologic features, biomarker expression, margin status, nodal involvement, and survival outcomes were compared. A second cohort of 441 ER-positive/HER2-negative early-stage carcinomas with available Oncotype DX results (335 IDC, 38 IDC-LL, 68 ILC) was also analyzed. RESULTS: IDC-LL accounted for 9.5% of all invasive carcinomas. Patients with IDC-LL (mean age 62) were older than IDC but younger than ILC. Grade 3 tumors were more frequent in IDC-LL than ILC (13.5% vs. 4.8%, p = 0.001) but less than IDC (30.5%, p = 0.0001). Hormone receptor positivity in IDC-LL (ER 89.1%, PR 79.6%) was intermediate between IDC and ILC, while HER2 positivity was lower than IDC and similar to ILC. IDC-LL also showed intermediate Oncotype DX and Magee scores. Overall survival was worse in IDC than in IDC-LL or ILC (p = 0.0006), while disease-free survival did not differ among groups. CONCLUSION: IDC-LL demonstrates clinicopathologic and molecular features intermediate between IDC and ILC. Recognition of IDC-LL as a distinct morphologic category is warranted to optimize diagnosis and surgical management.