DEAR DOCTOR: What is the link between smoking and bladder cancer? My urologist says smoking is one of the main causes, but until I got diagnosed with bladder cancer earlier this year, I had never heard about that connection.
DEAR READER: Your urologist is correct -- decades of studies have shown that smoking cigarettes is the greatest single risk factor for developing bladder cancer.
Bladder cancer is the fourth-most-common cancer in men, and it is less common in women. Of the 80,470 new cases of bladder cancer predicted for 2019, three-fourths will occur in men. The average age for diagnosis is 73, and the disease is less often seen in Latinos and African Americans.
Although earlier research suggested that smoking doubled or tripled an individual's risk, the most recent data indicate that cigarette smokers face four times the risk of developing bladder cancer than do non-smokers. A study conducted in 2011 connected cigarette smoking to half of all cases of bladder cancer that arose in both women and men.
To understand this connection to cigarette smoking, we should first talk a bit about bladder function and anatomy. The bladder is a hollow and flexible organ that is part of the urinary tract, which is the body's system for getting rid of waste and excess fluids. Each day the kidneys in adults filter up to 150 quarts of blood, which produces between 1 and 2 quarts of urine. In addition to water, salt and nitrogen products like urea, urine contains numerous additional waste products and impurities that the kidneys have stripped from the blood. The urine then moves from the kidneys to the bladder via a pair of tubes known as ureters. When the bladder begins to reach its capacity of 1.5 to 2 cups of urine, the brain receives signals that we recognize as the familiar urge to urinate. Urine exits the body via a duct known as the urethra.
Among the impurities filtered out of the blood by the kidneys are the thousands of byproducts, many of them toxic, contained in cigarette smoke. These include arylamines, which are known to be potent bladder carcinogens. And even as the number of smokers in the United States has dropped, cases of bladder cancer among smokers have increased. This has led researchers to draw a connection to changes in the array of chemicals used in the manufacturing of cigarettes.
When it comes to the chemical byproducts of smoking, they do their damage at least twice. The first time is in the respiratory system, particularly in the lungs. The second time is in the urinary tract, where they move from the kidneys to the bladder, where they are held in solution for hours at a time.
For people who have quit smoking, there's both good and bad news. Smoking cessation will reduce your bladder cancer risk. But the data shows that former smokers still have double the incidence of bladder cancer of nonsmokers. Unfortunately, exposure to secondhand smoke has been linked to increased risk as well. We have had a number of questions about bladder cancer and will continue the topic, including symptoms, treatment and outlook, in an upcoming column.
Eve Glazier, M.D., MBA, is an internist and associate professor of medicine at UCLA Health. Elizabeth Ko, M.D., is an internist and assistant professor of medicine at UCLA Health.