To me a carcinogen would be something we know to cause cancer, such as tobacco, excessive exposure to the sun, an occupation in which one works closely with chromium etc., exposure to radiation or asbestos, etc.
And a promoting factor would be a lifestyle choice we make that may increase our chances of actually getting cancer once exposed. For example, Japan has one of the highest per capita rates of cigarette consumption in the world, yet has one of the lowest rates of lung cancer. Their diet is thought to protect them from getting cancer. Foods such as watercress, green tea, lack of red meat, increased fish.
Promoting factors could include obesity, high saturated fat diet, excessive alcohol consumption, low fiber diet, perhaps red meat or a high protein diet (women who consume a lot of red meat are twice as likely to get lung cancer). Again, perhaps chlorinated drinking water, low fruit and vegetable intake, taking hormones.
My information is coming from the book "Eat to Beat Cancer" by J. Robert Hatherill, Ph.D.