I'm Dr. Greg Kalemkerian, medical oncologist and professor of Medicine at the University of Michigan. Today, we're going to talk about lung cancer risks and epidemiology. First, we're going to review the risk factors that cause lung cancer with a focus on tobacco smoke, and then we will review the epidemiology of lung cancer including the impact of race and gender on both incidence and survival. So, lung cancer is the most common cause of cancer-related death in the world and also the leading cause of cancer-related death in both men and women in the United States. Each year, more Americans will die from lung cancer than from colon, breast, pancreatic, and prostate cancer combined. So, lung cancer is a very large public health problem. Our pre-lecture question, which we'll come back to for the answer at the end of the lecture, is which of the following is true regarding the incidence rate of lung cancer in United States. It's highest in people between ages of 50 and 60, it's higher in women than in men, it is highest in African-American men, it is higher in African-American women than in white men. The second question, the lung cancer-specific mortality rate in the United States is now declining. What is the primary reason for this decline? The development of filtered cigarettes, the decreasing prevalence of tobacco smoking, the increasing popularity of mentholated cigarettes, the introduction of "low-tar" cigarettes, or the increasing use of lung cancer screening. So, we'll come back to the answers for those questions at the end of the lecture. So, what are the risk factors for lung cancer? Well, the major risk factor for lung cancer is tobacco smoke, as seen on this cross sectional CT image, where the arrow labelled Effect is pointing to a tumor in this person's right upper lung while the Cause arrow is pointing to a cross-sectional cut of a pack of cigarettes and a Bic lighter. So, the high-risk populations for development of lung cancer are primarily smokers and former smokers with a clear cut dose-response relationship. The more one smokes, the higher the risk of developing lung cancer. Other inflammatory lung diseases are also risk factors for lung cancer including chronic obstructive pulmonary disease such as emphysema, interstitial fibrosis, and multiple autoimmune disorders that can cause scarring within the lung. A number of occupational exposures have been linked to lung cancer risk including asbestos, silica, radon, mainly seen in miners, and then a few less-common occupational exposures. Prior lung cancer or prior head neck cancer, mainly related to tobacco smoking, are also very high risk factors for lung cancer. So, this slide, illustrates the relationship between the prevalence of cigarette smoking and the lung cancer mortality rate in both men and women. We can see across the bottom of this slide is the time element starting at 1900 when tobacco smoking was not very prevalent and the risk of lung cancer death was very, very low. Over time, as the prevalence of smoking rose, we see that after a temporal delay, the lung cancer mortality rate also began to rise. Initially, men were the ones who were doing most of the smoking, predominantly those who got hooked on cigarettes in the early 1900's, particularly during World War one. Then during World War two, women went into the workplace and became more independent and also began to smoke. We see that 20 years later, the mortality rate of lung cancer began to rise in women as well. As the smoking prevalence began to decline in the 1960's and 70's, we see that after another delay, the incidence of lung cancer, at least in men, began to decline. Thanks to initiatives by the tobacco companies such as the Virginia Slims campaigns, the lung cancer mortality rate in women continued to rise and only recently has begun to fall. So, lung cancer is a smoking-related disease with 85 to 90 percent of patients having a history of smoking. This slide illustrates that approximately 50 percent of people are now former smokers who develop lung cancer. Only about 10 to 15 percent of people who develop lung cancers have never smoked cigarettes. So, the median age at which lung cancer develops is around 70 years old. So, it is predominantly a cancer of the elderly. We see that there is a gradual increase up to about age 70 and then a slight decline in the incidence of lung cancer. On this slide, we see the incidence of lung cancer by gender, with males being the top row of filled in squares and females being the bottom line of filled in diamonds. We see that the incidence of lung cancer in men has been falling since about 1985 while the incidence in women had been gradually rising and has now plateaued and just begun to decline. The line indicated by the empty diamonds on this slide is the male to female ratio and we see that also has been declining as the incidence in men has decreased and the incidence in women has gradually risen. So, that it is now a little bit below 1.5 men for every woman who develops lung cancer. The survival of lung cancer also varies according to gender, with men doing significantly worse with lung cancer than women. We see both the two-year and five-year survival rates laid out here with women in the open boxes or triangles and men being indicated by the closed boxes or triangles, and we see that the survival rates for men are lower than women at each time point. This is a consistent finding not just in lung cancer but across most of our cancers. When we look at a race and compare Caucasians to African-Americans, we see that for women, which are the bottom two lines on this graph, the incidence of lung cancer is similar in both Caucasians and African-American women. However, in men, African-American men, as indicated by the blue line on top of this graph, clearly have a higher incidence of lung cancer than white men do. When looking at survival and evaluating survival by race, we see that both the two and five-year survivals are better amongst whites than they are amongst African-Americans. This difference seems to have widened in the past couple of decades with a poorer survival in African-American populations. So, coming back to our initial questions, which of the following is true regarding the incidence rate of lung cancer in the United States? It's highest in people between 50 and 60 years old, higher in women than in men, it's highest in African-American men, or it's higher in African-American women than in white men? We see that the correct answer is that the incidence rate is highest in African-American men who have a higher rate than Caucasian men but both groups of men do have higher rates than women do with African-American and white women having similar incidences of lung cancer. The second question, lung cancer-specific mortality rate in the United States is now declining. What is the primary reason for this decline? We see that the correct answer is the decreasing prevalence of tobacco smoking. Because the prevalence of tobacco smoking very clearly mirrors the incidence and mortality rates associated with lung cancer since 90 percent of people who develop lung cancer are tobacco smokers. We're hoping that the increasing use of lung cancer screening will also lead to a decline in mortality. However, this has not yet come to pass. So, the take-home points from this lecture are that lung cancer is the number one cause of cancer-related death both in the United States and in the world, that tobacco smoking accounts for 85 to 90 percent of all cases of lung cancer, smoking cessation is the most effective way to decrease lung cancer incidence and mortality, and lung cancer incidence is higher in African-Americans and in men in general. I want to thank you for your time.
