A few studies https://www.ncbi.nlm.nih.gov/pubmed/26514947 https://www.ncbi.nlm.nih.gov/pubmed/26514947 http://thorax.bmj.com/content/early/2016/11/25/thoraxjnl

A few studies https://www.ncbi.nlm.nih.gov/pubmed/26514947 https://www.ncbi.nlm.nih.gov/pubmed/26514947 http://thorax.bmj.com/content/early/2016/11/25/thoraxjnl-2016-208375.short?g=w_thorax_ahead_tab http://thorax.bmj.com/content/early/2016/11/25/thoraxjnl-201... http://cancerres.aacrjournals.org/content/early/2016/11/05/0008-5472.CAN-16-1359 http://cancerres.aacrjournals.org/content/early/2016/11/05/0... http://cebp.aacrjournals.org/content/4/8/895.short http://cebp.aacrjournals.org/content/4/8/895.short https://www.ncbi.nlm.nih.gov/pubmed/20479151 https://www.ncbi.nlm.nih.gov/pubmed/20479151 I am sure there is a meta-analysis somewhere but this would take a bit of time to find