Smoking causes cance. Smoking is the single largest avoidabble cause of cancer. There is no such thing as benign cancer. Most cancer arise denovo. A few like colon cancer and melanoma may arise from existing benign lesions and are not usually due to tobacco.
Yes. Smoking increases risk for oral, neck, lung, esophageal, bladder cancers.
It probably can. There are many times when smoking, often in combination with alcohol, can cause tumors, and make tumors more malignant, like esophageal cancer and lung cancer. Passive, or second-hand smoking, can increase risk of cancers, like lung, breast, and renal. Smoking has been shown to be a promoter of many cancers like lung, anal, and pancreatic. It interferes with apoptosis or death of cancer cells.