The relationship between statins and breast cancer prognosis varies by statin type and exposure time: a meta-analysis

Purpose: Breast cancer is the most common cancer in females and the leading cause of death worldwide. The effects of statins on breast cancer prognosis have long been controversial; thus, it is important to investigate the relationship between statin type, exposure time, and breast cancer prognosis. This study sought to explore the effect of statins, as well as the different effects of statin solubility and variable follow-up times, on breast cancer prognosis. Methods: We searched the MEDLINE (via PubMed), EMBASE (via OvidSP), Cochrane Library, and ISI Web of Knowledge databases using combinations of the terms “breast neoplasms[MeSH],” “statins” or “lipid-lowering drug,” “prognosis” or “survival,” or “mortality” or “outcome” with no limit on the publication date. We searched the databases between inception and October 15, 2016. Reference lists of the included studies and relevant reviews were also manually screened. The initial search identified 71 publications, and 7 of these studies, which included a total of 197,048 women, met the selection criteria. Two authors independently screened each study for inclusion and extracted the data. The data were analyzed using Stata/SE 11.0. Results: Overall statin use was associated with lower cancer-specific mortality and all-cause mortality, although the benefit appeared to be constrained by statin type and follow-up time. Lipophilic statins were associated with decreased breast cancer-specific and all-cause mortality; however, hydrophilic statins were weakly protective against only all-cause mortality and not breast cancer-specific mortality. Of note, one group with more than 4 years of follow-up did not show a significant correlation between statin use and cancer-specific mortality or all-cause mortality, whereas groups with less than 4 years of follow-up still showed the protective effect of statins against cancer-specific mortality and all-cause mortality. Conclusions: Although statins can reduce breast cancer patient mortality, the benefit appears to be constrained by statin type and follow-up time. Lipophilic statins showed a strong protective function in breast cancer patients, whereas hydrophilic statins only slightly improved all-cause mortality. Finally, the protective effect of statins could only be observed in groups with less than 4 years of follow-up. These findings are meaningful in clinical practice, although some conclusions contradict conventional wisdom and will thus require further exploration.