As long as there is doubt like this, I think erring on the side of caution is a good thing particularly for those of us with other risk factors.IGF-1 (insulin growth factor 1). This growth factor has recently been the subject of a research study into breast cancer risk. Women with high levels of IGF-1 in their blood may have a higher risk of breast cancer. Some scientists think that high IGF-1 levels may also encourage an existing breast cancer to spread, but this has not been proved. There are also reports of increased risk of colon cancer with high IGF-1 levels. But we don't know if the high IGF-1 levels come from milk and dairy products in the diet, or from some other cause.