Among women who had high cholesterol, those who took statins for 10 years or longer more than doubled their risk of breast cancer compared to those who didn’t:
Long-term Statin Use And Risk Of Ductal And Lobular Breast Cancer Among Women 55-74 Years Of Age, Cancer Epidemiology, Biomarkers & Prevention, September 2013
Why? They don’t know:
The biology underlying an association between statin use and breast cancer risk is uncertain.
However:
We observed that risks were highest among long-term current users suggesting that statins may act as promoters of breast carcinogenesis.
What about short term use?
This finding does not rule out the possibility that shorter term statin use may have no effect … on the development of breast cancer.
It’s probably not because the women had high cholesterol to begin with:
Our finding of a greater than 2-fold increased risk of breast cancer among current long-term statin users in analyses restricted to study participants reporting a history of high cholesterol is evidence that confounding by indication does not account for the excess of breast cancer cases among statin users.
If this association holds up, it’s a ticking time bomb:
Approximately a quarter of all United States women over the age of 45 report current use of one of the seven different statin drugs on the market today.
Fanatic Cook 
You can lower your cholesterol naturally by eating a low-fat plant-based diet. Remember this?
<a href="https://fanaticcook.com/2014/08/04/president-elect-of-american-college-of-cardiology-promotes-vegan-diet-after-lowering-his-ldl-from-170-to-90-in-6-weeks/" target=President-Elect Of American College of Cardiology Promotes Vegan Diet After Lowering His LDL Cholesterol From 170 To 90 In 6 Weeks
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A 2005 meta-analysis, focused on on seven statin trials and breast cancer incidence, found no effect, and the largest meta-analyses of randomized trials of statins and cancer to date found no effect on any cancer. In Denmark’s population, statin use was associated with a 15% reduction in cancer mortality and simvastatin (only) linked to 10% reduced breast cancer recurrence. I suspect the smallish Seattle study is confounded by issues with its case-control design and medical care access issues (eg. those having mammograms at more regular intervals may have more intensive medical care generally).
Statin use carries numerous risks of liver dysfunction, myopathy, and cataracts, so it remains better to achieve target LDL levels with very low-saturated fat, whole food, plant based diets. But the aggregate data doesn’t appear to support a breast or other cancer risk with statin use.
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This study I posted looked at long-term statin use. Many prior studies did not. So meta-analyses were often based on shorter-term statin use.
The Bonovas meta-analysis you mention said:
And the large Emberson meta-analysis had a median statin use of just 4.8 years. Also, “Most of the trials in this report were supported by research grants from the manufacturers of statins.”
This was not the only study to report an increased risk. In a randomized double-blind control trial of pravastatin, there was a 12-fold increased risk of breast cancer over 5 years.
I think the strength of this study is the strong 2-fold increased risk, and that it looked at the effect of taking statins for 10 years or more. Cancer can take decades to make itself known.
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