Building on our previous analyses of circulating levels of lymphocytes in primary breast cancer patients [17], we have now examined relative numbers and locations within breast cancer tissues of lymphocytes showing positivity for markers CD20 (B cells), CD4 (helper T cells), CD8 (cytotoxic T cells) and FoxP3 (regulatory T cells) in tumours from the same patients (n = 62). Here, CD4 is linked to breast cancer.