Toward targeted therapeutics for lobular breast cancer.

Despite growing recognition of invasive lobular carcinoma (ILC) as a biologically and clinically distinct subtype of breast cancer, ILC remains understudied. Most contemporary therapeutic trials continue to enroll patients predominantly with invasive ductal carcinoma/invasive carcinoma of no special type and rarely stratify by histology. As a result, ILC's unique disease biology, characteristic loss of E-cadherin function, diffuse growth pattern, and distinct metastatic tropism remain underrepresented in evidence that guides systemic therapy recommendations. In this Review, we examine key molecular alterations and emerging therapeutic targets in ILC, emphasizing recent preclinical discoveries that identify subtype-specific therapeutic vulnerabilities and guide the development of histology-specific treatment approaches for this unique disease. In combination with endocrine therapies, effective targeting in ILC may require a multilayered strategy that extends beyond genomic alterations to leverage ILC's specific estrogen receptor-associated proteins, metabolism, and tumor microenvironment. Future clinical trial frameworks incorporating prespecified ILC cohorts, tailored endpoints, and coclinical approaches enabling parallel testing in patients and patient-derived models could help accelerate the development and evaluation of ILC-targeted therapeutics.