When assessing specific immunological differences between SLNs from BC patients and NLNs from healthy individuals, we found that the CD28/CTLA-4 ratio was much higher in the C1 and C2 clusters and in the OSNA pN0 samples than in the NLNs, suggesting an immune response activation in tumour-draining SLNs, particularly in C1 SLNs, which exhibited higher CD80 expression levels. Here, CTLA4 is linked to breast cancer.