Immune Profiling the Axilla with Fine Needle Aspiration is Feasible to Risk-Stratify Breast Cancer
Whether breast cancer (BC) has metastasised to the regional axillary lymph nodes (ALN) is an important prognostic factor that directs the extent of axillary surgery. However, surgically clearing the axilla carries morbidity, so less invasive methods of risk-stratifying patients are needed. ALN fine needle aspiration (FNA) is currently used to detect BC metastases, but these samples also contain immune cells. Here we show that FNA acquires sufficient leukocytes for comprehensive immunophenotyping of reactive, patient-derived ALN. All CD4+ and CD8+ T cells subsets (naive, terminal effector, central and effector memory) and rarer (<2%) natural killer (NK) and plasmacytoid dendritic cell (pDCs) populations are represented. Importantly, the immune cell profile of one reactive ALN appears to reflect the immune status of the patients axilla. We show that FNA captures immune differences between patients with [≤]1 or [≥]2 metastatic ALN. Significantly increased numbers of naive CD4+ T cells, but significantly fewer terminal effector, central memory and effector memory subpopulations, were obtained from patients with [≥]2 metastatic ALN. Moreover, despite their sparse distribution pattern on whole-section immunohistochemistry (WSI), FNA revealed that CD56+ NK cell activation receptors were decreased in patients with [≥]2 metastatic ALN. Finally, FNA captured a significant decrease in pDCs in patients with [≥]2 metastatic ALN, despite their clustered distribution pattern on WSI. In summary, FNA is not only feasible for sampling leukocytes from reactive, patient-derived ALN, but also identifies immune cell profiles that reflect axillary tumour burden in BC. Thus, this technique could be used to risk-stratify BC patients in future.