Clinical characteristics and prognostic impact of HER2-ultralow breast cancer and tumor-infiltrating lymphocytes (TILs).

ABSTRACT:

Purpose

HER2 expression is crucial in breast cancer classification and treatment. Traditionally, tumors were categorized as HER2-positive or HER2-negative, but HER2-low (IHC 1 + or 2 + without ISH amplification) has emerged as a new classification. Among HER2-negative cases, HER2-ultralow (≤ 10% faint HER2 staining) and HER2-null (completely HER2-negative) have been proposed. While differences between HER2-low and HER2-zero tumors are studied, little is known about the clinical and prognostic characteristics of HER2-ultralow breast cancer. This study aimed to clarify the clinical characteristics, immune microenvironment, treatment response, and prognosis of HER2-ultralow tumors, with HER2-null and HER2-low tumors analyzed as comparators.

Methods

A retrospective analysis of 2

SUBMITTER: Takada K 

PROVIDER: S-EPMC12751392 | biostudies-literature | 2025 Nov

REPOSITORIES: biostudies-literature