Comparing Rates of Index Mastectomy and Conversion to Mastectomy after Breast-Conserving Surgery for Invasive Ductal Carcinoma, Invasive Lobular Carcinoma, and Mixed Invasive Ductolobular Carcinoma

Document Type

Conference Proceeding - Restricted Access

Publication Date

5-8-2026

Abstract

Invasive ductal (IDC) and invasive lobular (ILC) carcinoma represent the most common histopathologic subtypes of breast cancer. Mixed invasive ductolobular carcinoma (MIDLC), characterized by features of both ductal and lobular differentiation, remains less well defined in the literature. Prior analyses of national databases have suggested higher mastectomy rates in patients with ILC and MIDLC compared to IDC, yet institutional-level data characterizing these trends are limited. This study aimed to evaluate surgical management patterns, including rates of mastectomy and conversion from breast-conserving surgery (BCS), among patients with MIDLC compared to IDC and ILC within an institutional cohort.

A retrospective review was performed of all patients diagnosed with IDC, ILC, or MIDLC who underwent breast surgery between 2019 and 2023 at our institution. Demographic, clinicopathologic, and treatment data were abstracted from medical records. Comparative analyses were conducted between histologic subgroups to assess associations with tumor biology, neoadjuvant and adjuvant therapy, and operative approach.

A total of 1201 patients were identified: 13.5% (n=162) with MIDLC, 13.9% (n=167) with ILC, and 72.6% (n=874) with IDC. The mean age was 61.2 years (SD=12.8). There were no significant differences in patient demographics, clinical N stage, or overall clinical stage by histologic subtype. The majority of patients underwent BCS as their index procedure (72.8%, n=874), with 2.0% (n=24) later converting to mastectomy. Conversion rates from BCS to mastectomy did not differ significantly among histologic groups (IDC 2.7%, ILC 3.1%, MIDLC 3.8%, p=0.87). ILC patients were more likely to undergo upfront mastectomy compared with IDC and MIDLC (41.9% vs 29.0% vs 34.6% respectively, p=0.015). Estrogen-receptor (ER) and/or progesterone-receptor (PR) positivity was more frequent among MIDLC and ILC compared to IDC (ER+ 98.8%, 98.8%, and 78.9% respectively, p< 0.001; PR+ 87.7%, 81.4%, and 71.6% respectively, p < 0.001). Conversely, HER2 positivity was higher among IDC patients (12.6%, p< 0.001) compared to MIDLC (6.2%).

Histologic subtype was not associated with conversion from breast-conserving surgery to mastectomy. Patients with ILC were more likely to undergo initial mastectomy, while MIDLC demonstrated overlapping biologic and clinical features of both ductal and lobular carcinoma. These findings support recognition of MIDLC as a distinct entity that merits further investigation to guide management strategies.

Comments

2026 Research Day Corewell Health West, Grand Rapids, MI, May 8, 2026. Abstract 1963

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