Relationship between serum lipid levels and the immune microenvironment in breast cancer patients: a retrospective study.

Background: Therapeutic agents for dyslipidaemia, in particular statins, have been recently reported to suppress growth and metastasis of breast cancer. However, the predictive value of lipid control in breast cancer patients has not been discussed sufficiently. In addition, though immunometabolism is a relatively novel approach for tumour immunotherapy, the relationship between lipid metabolism and immune status has not been well documented. We therefore investigated the effects of lipid metabolism on antitumour immune response and cancer prognosis.

Methods: Except for patients with ductal carcinoma in situ, 938 patients treated with curative surgery were examined. The correlation between treatment for dyslipidaemia or serum lipid levels and clinicopathological features, including the prognosis, was evaluated retrospectively. Also, we stratified these results by intrinsic subtype of breast cancer, menopause, and type of therapeutic agents for dyslipidaemia. Moreover, neutrophil- to-lymphocyte ratio (NLR) and tumour-infiltrating lymphocytes (TILs) were used as indicators of systemic and local immune status, respectively.

Results: Of 194 patients treated for dyslipidaemia, recurrence-free survival (RFS) and overall survival (OS) did not differ significantly between users of drugs for dyslipidaemia and non-users (p = 0.775 and p = 0.304, log-rank, respectively). Among postmenopausal, hormone receptor (HR)-positive/human epidermal growth factor receptor 2 (HER2)-negative breast cancer patients treated for dyslipidaemia, the good serum lipid control group had significantly better RFS (p = 0.014, log-rank), lower postoperative NLR (p = 0.012), and higher TILs in resected tissues (p = 0.024) than the poor control group. Multivariate analysis showed that postoperative serum lipid levels were a risk factor for recurrence (hazard ratio = 4.722, 95% confidence interval 1.006-22.161, p = 0.049).

Conclusions: Good control of serum lipid metabolism may improve the tumour immune microenvironment and prognosis in postmenopausal HR-positive/HER2-negative breast cancer patients.