Causes of Cancer
The use of Tobacco products is the single most important factor in increasing cancer risk. The hazards of Tobacco are due to a large number of carcinogenic compounds: those which are already in the Tobacco product and those that form during smoking.
It is well understood what effect smoking has on the production of Lung Cancer. The greater the risk of getting lung cancer, the younger people start smoking, the more they smoke regularly, and the longer they continue to smoke. [4, 5] If a person has smoked 20 cigarettes a day for 50 years, his or her risk of developing Lung Cancer is nearly 50 times greater than that of non-smokers. The risk of lung cancer, after quitting smoking, exceeds those of non-smokers of the same age quite rapidly but it does not fall to the same level. People who have smoked the longest benefit from giving up. Smoking is a major cause of larynx cancer, and also has an impact on oral, pharyngeal, kidney, pancreatic, oesophageal, cervical, and bladder cancer. Smoking could increase Breast Cancer risk slightly, too. 
In recent years, strong evidence has accumulated in studies about the carcinogenic potential of using snus. The risk of developing oral and pharyngeal cancer, pancreatic and gastric cancer and oesophageal cancer is significantly higher for those who use snus than for those who do not use Tobacco products. [7-9] Over the last few years, electronic smoking has increased significantly. It is studying its impact on health.
With the combination of smoking and other factors, the risk of cancer also increases considerably. Smoking and outdoor work together, for example, increase the risk of lip cancer by as much as 15-fold, while outdoor work or smoking alone only doubles the risk of lip cancer.  Smoking increases the effect of asbestos and other chemicals used in the workplace, which are not especially harmful by themselves.
There is a direct causal link between alcoholic beverage use and many cancer types. There is compelling evidence that heavy Alcohol consumption raises the risk of cancers of the throat, pharynx, larynx, oesophagus, liver, bowel and breast. 
For example, four regular doses of Alcohol (50 grams of ethanol) roughly double the risk of oral and pharyngeal cancer. Other factors that contribute to the Alcohol impact. Drinking Alcohol and smoking together, for example, very significantly increase the risk of nasal, pharynx and larynx cancers.
There is no safe level of Alcohol intake about breast cancer, although the risk of cancer is increased in direct proportion to the amount of Alcohol consumed on a daily basis. The biggest risk factor is the volume of ethanol consumed. Strong Alcohol consumption raises cancer risk and causes many apparent health issues. The type of alcoholic drinks consumed does not affect cancer risk significantly.
Diet is a dynamic combination of components, having joint and opposite effects that are hard to accurately predict. Food is known to have the greatest effect on the occurrence of oesophagus, colon, rectum, kidney, prostate, lung, and Breast Cancer.
Nutritional fat increases the risk of breast, colon and Pancreatic Cancer according to a number of animal tests. However, information about people is not yet sufficiently convincing to allow for a definite judgment of the effects of fat on cancer risk. Cancer tissue requires energy and minerals, so nutrition can have an effect not only on cancer production but also on its growth.
It is probable that dietary fibres can protect against Colorectal Cancer.  In addition, diets high in fruits and vegetables lower the risk of many cancers.
There was a comprehensive study of the effect of red and processed meat on the incidence of some types of cancer. High processed meat intake is associated with increased risk of colorectal and gastric cancer. Red meat is also a potential risk factor for both colorectal and pancreatic and Prostate Cancer. 
The key interest in the vitamin and cancer connection has been in carotenoids, vitamins A, E, C , and D, and folate. Vitamin products have also been tested for cancer prevention, but none of these have yet been shown to prevent cancer alone or in any combination.  Therefore, the key factor for cancer prevention appears to be a healthy overall lifestyle, not specific dietary factors.
Some processes in food preparation cause chemical changes which lead to the formation of cancer-causing substances in the food. Smoking and grilling fatty foods over an open fire or other high temperature will produce small quantities of polycyclic aromatic hydrocarbons ( PAHs) on the food’s surface, which will increase cancer risk. High salt and salt-conserving foods raise the risk of gastric cancer.