I personally think that it is way too early to even speculate on this. And what is really upsetting is that the doctor wants to blame it on the chemicals in the e-cigarette. Most e-cigarette brands disclose the ingredients. Take a look at this website and you will see what's in the smoke juice. In general it is water, nicotine, propylene glycol and/or vegetable glycerin, and ingredients for flavor. Source: http://www.ecigarettes365.com/new
On the other hand we know that tobacco cigarettes contain thousands of carcinogens!