CYP19A1 and breast cancer: Aromatase is expressed from the stroma, including adipose tissue; hence, serum lipid control by treatment for dyslipidaemia may modulate components of the tumour immune microenvironment, such as cancer-associated fibroblasts, and suppress the growth of AI-resistant breast cancer cells (Fig. 5) In the future, immunohistochemical analyses of primary or recurrent tumours and investigation of immune mechanisms may facilitate both the understanding of the relationship between lipid metabolism and the tumour immune microenvironment as well as the prediction of prognosis.