Clinicopathologic and Immunophenotypic Classification of Invasive Lobular Carcinoma with Histiocytoid Features

Area of Science:

• Oncology
• Pathology
• Genetics

Background:

• Histiocytoid lobular breast carcinoma is a rare invasive lobular carcinoma subtype.
• Characterized by bland nuclei, granular cytoplasm, and often triple-negative, androgen receptor (AR)-positive status.
• Theorized to represent apocrine differentiation, with anecdotal evidence suggesting favorable outcomes.

Purpose of the Study:

• To investigate the clinicopathologic features and outcomes of histiocytoid lobular breast carcinoma.
• To analyze the immunohistochemical profiles of these tumors.
• To assess survival and metastatic disease in a cohort of patients.

Main Methods:

• Retrospective review of 12 patients diagnosed between 2008-2021.
• Analysis of hematoxylin and eosin slides and immunohistochemical stains (ER, PR, HER2, AR, EGFR, KRT5/6).
• Evaluation of patient outcomes, including survival and metastasis.

Main Results:

• 12 eligible patients identified with histiocytoid features.
• Immunophenotypes varied: 4/12 triple-negative/AR-positive, 7/12 Luminal B, 1/12 HER2-enriched.
• No disease-related deaths; 2/12 presented with distant metastasis.

Conclusions:

• Histiocytoid lobular breast carcinoma is a morphologic variant with apocrine features.
• Exhibits a variable immunohistochemical profile and clinical behavior.
• Further subclassification may aid in distinguishing indolent from aggressive cases.