TIL（肿瘤浸润淋巴细胞）的局灶性热区与弥漫性免疫亚型：AI 驱动的空间聚类分类及其与三阴性乳腺癌 HER2 表达的临床相关性

This study aimed to define spatial immune subtypes of tumor-infiltrating lymphocytes (TILs) using artificial intelligence (AI)-powered analysis and investigate their association with distinct human epidermal growth factor receptor-2 (HER2) expression levels, response to neoadjuvant chemotherapy (NAC), and patient survival outcomes in triple-negative breast cancer (TNBC).

We conducted a multicenter study involving TNBC patients receiving NAC, stratified into HER2-0, HER2-ultralow, and HER2-low subgroups. An AI-based cell classifier was employed to identify TILs (AI-TILs) and extract spatial coordinates from pathology images. Using unsupervised learning of spatial clustering analysis to identify immune subtypes. The performance of the AI model was benchmarked against four experienced pathologists. Associations among TILs spatial subtypes, HER2 status, NAC response including pathologic complete response (pCR) and residual cancer burden (RCB), and survival outcomes were systematically evaluated.

AI-TILs demonstrated strong agreement with both senior pathologists, and unsupervised clustering revealed two spatial subtypes: the focal hotspot subtype and the diffuse immune subtype, the latter exhibited broader TIL hotspot areas, lower peak densities, higher pCR rates, and significantly prolonged disease-free survival (DFS). RCB-III status was inversely associated with the diffuse immune subtype, suggesting a link between diffuse immune subtype and good NAC response. Postmenopausal status was independently linked to the focal hotspot pattern. Although HER2 expression was associated with TILs spatial subtypes, it was not an independent influencing factor. In the HER2-low subgroup, the diffuse subtype was significantly associated with better pCR and lower RCB scores, whereas no such relationship was observed in HER2-0 or HER2-ultralow groups. Alluvial and standardized residual analysis further validated that focal hotspot/HER2-low tumors were enriched in RCB-III (residual = 3.26), while diffuse/HER2-low tumors were enriched in RCB-0 (residual = 1.30), suggesting divergent trajectories of immune architecture and chemoresponsiveness.

This study distinguished focal hotspot and diffuse immune subtypes of TILs with distinct clinical implications in TNBC. The diffuse immune subtype correlated with enhanced NAC response and favorable prognosis, particularly in HER2-low TNBC. These findings highlighted the spatial immune architecture as a promising biomarker to refine treatment stratification and deepen our understanding of immune heterogeneity in HER2-low TNBC.