If you smoke more than a pack or two of cigarettes a day, you are classified as a heavy smoker. And new research also shows the longer you smoke, the greater your risk of developing life threatening diseases. One of them is a deadly form of kidney cancer.

　　The World Health Organization (WHO) is not exaggerating when it says tobacco use is one of the biggest public health threats the world has ever faced. But each year, according to the WHO, at least seven million people, or one in every 10 adults around the globe, dies of a smoking related disease. Adding to that bad news, the health organization predicts that almost half of those who currently smoke will die from a disease associated with tobacco.

　　Smoking is linked to heart disease, stroke and in the case of cancer, begins in the lung where it is inhaled.

　　Dr. Thomas Polascik of Duke University's Cancer Institute says the smoke travels through the lungs, the bloodstream and makes its way eventually to the kidneys, where tumors can grow quite large before they are detected.

　　"Unless a patient has some sort of pain or perhaps blood in the urine, it may not come to their attention," Dr. Polascik stated.

　　Often the patient comes into the hospital emergency room with abdominal pain or indigestion, and an imaging device like the MRI or CT scan identifies the tumor.

　　Previous research had already established the connection between tobacco use and kidney cancer, but the scientists at Duke University studied the medical records of more than 800 patients who had undergone surgery and found something more serious: the onset of advanced kidney cancer.

　　Dr. Polascik says the kidney cancer patients were divided into three groups, current and former smokers and those who never smoked. Their risk of advanced kidney cancer was based on two factors, how much they smoked every day and over how long a period of time.

　　"We found that for people who have smoked, say, up to 10 years, the risk only increases by six percent. Whereas, if you smoked between 10 and 20 years, that risk goes up to 45 percent," Dr. Polascik explained. "Of course, if you smoke over 30 to 40 pack years, your risk increases to 80 percent compared to non-smokers."

　　But what are the odds of advanced renal cancer if the patient has either stopped smoking long ago or never smoked at all? "After a number of decades, maybe 20 or 30 years of non-smoking or having to quit smoking, one's odds will be almost the same as a non-smoker, but not quite," he said.

　　The doctors say this discovery could provide another incentive for smokers to quit. The sooner they stop, the greater their chance of survival. Dr. Polascik says in the past, patients with advanced kidney cancer had about an eight percent chance of surviving another five years. But imaging techniques such as the MRI and the CT scan can identify tumors when they are smaller.

　　"With these smaller tumors we can typically surgically excise them [cut them out] and the survival rate is like in the order of 90 to 95 percent,” he said. “It's quite high."

　　The researchers at Duke University say more study needs to be done, perhaps by identifying in the laboratory how smoking by-products interact in the body's organs to form malignant tumors. The study appears in the Journal of Clinical Oncology.