Gender gap for lung cancer rates narrowing

Broadest-to-date US lung cancer study compares gender with incidence

Results of the most comprehensive analysis to date of the impact of gender differences in lung cancer incidence in the United States indicate that lung cancer rates among men are on the decline, while the rate in women remains steady. A new study in the March issue of CHEST, the peer-reviewed journal of the American College of Chest Physicians, shows that, in addition to the unequal incidence of lung cancer in men and women, there are other gender-linked differences, including subtype of lung cancer and survival rate.

“Traditionally, lung cancer has been viewed as a disease of older male smokers, but that is not necessarily the case,” said the study’s author, Gregory P. Kalemkerian, MD, University of Michigan Medical Center, Ann Arbor, MI. “This data supports the fact that lung cancer is becoming a bigger problem in women every year. If these current trends continue, in 10 to 15 years, the incidence of lung cancer will be identical for women and men.”

Researchers from the University of Michigan Medical Center and Wayne State University analyzed data of 228,572 patients (81,843 women and 146,729 men) with lung cancer who were registered in the national, population-based Surveillance, Epidemiology, and End Results (SEER) database between 1974 and 1999. Researchers found that the incidence of lung cancer in men reached a peak in 1984, when 72.5 of every 100,000 men had the disease, then declined to 47 per 100,000 men in 1991. In sharp contrast, the incidence of lung cancer in women continued to rise to a peak with 33.1 per 100,000 women in 1991, and then remained relatively stable at 30.2 to 32.3 per 100,000 women from 1992 to 1999. These variations have resulted in a male/female incidence ratio change from 3.56:1 in 1975 to 1.5:1 in 1999. For both men and women, the median age of diagnosis was 66 years. Women made up 40.9% of patients under the age of 50 but only 35.4% of patients over the age of 50.

“The fact that women appear to be overrepresented among women under the age of 50 is a reflection of increased smoking prevalence among women, especially early in the study period,” said Dr. Kalemkerian. “There is still controversy as to whether or not women are more susceptible to tobacco carcinogens, but our findings suggest that women and men are affected differently by their tobacco use. For example, nearly half the women (44.7%) developed adenocarcioma, while the men were most likely to develop squamous cell carcinoma (36.3%).”

The study also found that women had significantly higher rates of survival at every stage of the disease. From 1975 to 1987, the five-year survival rate was 12.1% greater in women than in men, and, from 1988 to 1999, women’s five-year survival rate was 6.5% higher. Even when researchers compared the survival of early-stage patients who all underwent surgery, they found that after two years, 74.3% of women survived, compared to 66.0% of men, and, after five years, 56.8% of women survived, compared to only 48.3% of men. Researchers speculate that the difference in survival can be attributed to men having more frequent comorbid conditions, such as heart disease or severe emphysema. Aside from the stage of disease, being a man was the factor that most negatively impacted survival among patients.

“Lung cancer is the leading cause of cancer-related mortality for women in the United States,” said Paul A. Kvale, MD, FCCP, President of the American College of Chest Physicians. “Although it used to be considered a male smoker disease, this shortening gender gap clearly illustrates a behavior shift over recent years in women. This study reinforces the need for physicians to focus on women who are susceptible to lung cancer.”