Clinical Significance of Tumour-Infiltrating B Lymphocytes (TIL-Bs) in Breast Cancer: A Systematic Literature Review

SIMPLE SUMMARY: Breast cancer is the most frequently diagnosed cancer among women worldwide. Although there have been significant advances in the past decade in our understanding of breast cancer biology and the choice of treatment, mortality remains high, especially among certain subgroups of patients. The advent of onco-immunology as a burgeoning speciality of precision medicine designed to heighten the antitumor response of the immune system in cancers like melanoma has not been associated with impressive results in breast cancer. Most research efforts have focused only on T lymphocytes with little regard to other potentially important players, including B lymphocytes. This review aims to summarise studies that have assessed the clinical significance of tumour-infiltrating B lymphocytes in breast cancer and explore future research directions that may shed further light on understanding the role of B lymphocytes in breast cancer. ABSTRACT: Although T lymphocytes have been considered the major players in the tumour microenvironment to induce tumour regression and contribute to anti-tumour immunity, much less is known about the role of tumour-infiltrating B lymphocytes (TIL-Bs) in solid malignancies, particularly in breast cancer, which has been regarded as heterogeneous and much less immunogenic compared to other common tumours like melanoma, colorectal cancer and non-small cell lung cancer. Such paucity of research could translate to limited opportunities for this most common type of cancer in the UK to join the immunotherapy efforts in this era of precision medicine. Here, we provide a systematic literature review assessing the clinical significance of TIL-Bs in breast cancer. Articles published between January 2000 and April 2022 were retrieved via an electronic search of two databases (PubMed and Embase) and screened against pre-specified eligibility criteria. The majority of studies reported favourable prognostic and predictive roles of TIL-Bs, indicating that they could have a profound impact on the clinical outcome of breast cancer. Further studies are, however, needed to better define the functional role of B cell subpopulations and to discover ways to harness this intrinsic mechanism in the fight against breast cancer.