Further study limitations include the lack of high-dimensional immunohistochemistry markers to delineate more subtypes of TILs21 beyond CD4/CD8/FOXP3, other key cell types such as macrophages, B cells20 and cancer-associated fibroblasts in the tumour ecosystem, as well as the use of 2D slides that do not fully represent the 3D ductal structure. Here, CD4 is linked to cancer.