Statins link to breast cancer protection

If you have been diagnosed with, or are at higher risk of getting, breast cancer, you might want to be on a cholesterol-lowering statin drug, according to a study posted on pre-print website bioRxiv. It probably also helps if you live in Scandinavia.

Led by Signe Borgquist, an oncologist at Lund University in Sweden, the study, which is yet to be peer reviewed, examined the fate of more than twenty thousand Swedish women diagnosed with breast cancer between 2005 and 2008. By 2012, 2669 were dead from causes linked to the cancer.

“In Sweden, around 20% of the adult female population is currently prescribed a statin,” the researchers say.

That figure was reflected in the study, with more than 2600 women taking statins before the cancer diagnosis and just over 4600 using the drug afterwards. Taking a statin, the researchers found, was protective.

The effect was biggest in women taking statins before they got cancer. The likelihood of dying from breast cancer was 23% lower in women using statins regularly before the diagnosis, compared to women who used them sporadically or not at all. Taking the drugs after the cancer diagnosis also helped, with statin-users logging a 17% lower chance of death.

How could statins, the blockbuster cholesterol pills whose star performer Lipitor (also known as atorvastatin) was awarded best-selling drug of all time in 2011, be good for breast cancer?

A couple of reasons. The body needs cholesterol to make oestrogen, the female hormone that triggers faster growth in some breast cancers. Cut cholesterol with a statin and you might also slow growth of oestrogen-sensitive tumours.

But the cholesterol pathway also has intimate connections with something heroically dubbed “the guardian of the genome”. P53, the so-called “tumour suppressor gene”, plays a key role in stopping cells turning cancerous. Mutated versions of the gene, however, can have the opposite effect, causing runaway cell growth.

When statins target the cholesterol pathway, unfriendly things also happen to mutant P53, which could account for any anti-cancer effect the drugs may have.

As the authors note, however, this is not the first study to draw a salutary link between statins and breast cancer. Two of those studies, it turns out, also came from Scandinavia; Denmark and Finland to be exact.

But on the other side of the North Sea it gets less exciting. Studies from the British Isles have shown little evidence for such an effect, although why that population might return conflicting results isn’t clear.

John Hopper from the School of Population and Global Health at the University of Melbourne in Australia points out the study has limitations.

“This is just an observational study so the associations could be due to factors not able to be taken into account,” he says.

Indeed, the authors volunteer they had no access to data on “adjuvant therapy” – treatments the women might have had on top of the primary, often surgical one. These can include chemotherapy, anti-oestrogen drugs and radiation. They note, however, such treatments were quite uniform in Sweden during the study period.

They also concede the possibility of a “healthy user bias”. Women taking statins are more likely to be health-aware and so seek breast cancer screening, reducing their risk through early detection.

The upshot is that evidence from gold standard, randomised controlled trials is sorely needed.

“There is a need for confirmative results based on clinical trials before statin treatment can be recommended for patients newly diagnosed with breast cancer,” the authors conclude.