VANCOUVER, B.C. – Small cell lung cancer presentation varies by sex and race, according to a retrospective analysis of U.S. national data spanning a 32-year period.
Women were more likely than men to have limited disease at diagnosis and had better survival, Dr. Shagun Arora reported at the annual meeting of the American College of Chest Physicians. African Americans were younger than whites at diagnosis, and the small cell type made up a smaller proportion of all lung cancers in African American patients than in white patients.
Dr. Shagun Arora
Possible explanations include differences in patterns of smoking and susceptibility to the deleterious effects of tobacco smoke, as well as hormonal factors, according to Dr. Arora, an internist at McLaren Regional Medical Center in Flint, Mich.
Using histologic codes, the investigators identified all cases of small cell lung cancer in the Surveillance, Epidemiology, and End Results (SEER) database among white and African American patients between the years 1973 and 2005.
Analyses were based on 70,886 patients with small cell lung cancer. About 91% were white and 55% were male.
During the study period, the male-to-female ratio in the proportion of all lung cancers that were of small cell type fell from 2.6 to 0.9, which mainly reflected a rise among women, Dr. Aurora said.
Age at presentation did not differ by sex. But women were more likely to have disease that was limited in stage (that is, confined to one hemithorax) at diagnosis than were men (35% vs. 30%).
And although cancer-specific survival improved for both sexes over time, it was consistently longer for women than for men. At the end of the study period, 2-year survival was approximately 20% among women, vs. 15% among men.
"We all know that small cell lung cancer is very closely related to smoking," Dr. Arora commented. Hence, differences between the sexes in smoking patterns may explain some of these findings.
"Females began smoking 20 years after males," she noted, and their smoking rates have been slower to decline. In addition, "females are more prone to tobacco effects: They are 1.5 times more likely to develop lung cancer than males with the same smoking habits."
The study did not use multivariate or stage-stratified analysis, Dr. Arora said; hence, the less-extensive disease of women at presentation may have contributed to their better survival. Nonetheless, this finding "begs the question of a possible hormonal factor."
Study results for race showed that the proportion of all lung cancers that were of small cell type was consistently lower among African American patients than among white patients throughout the study period. As of 2005, the value was 9% compared with 12% for white patients.
Age at presentation was younger among African American patients than among white patients. For example, roughly 50% of African American patients received their cancer diagnosis before age 64, compared with 40% of white patients. But the two racial groups did not differ with respect to the stage at diagnosis or cancer-specific survival.
Here, again, smoking patterns and susceptibility may explain some of the observed differences, according to Dr. Arora.
On the one hand, African American smokers smoke fewer cigarettes daily than do their white peers and start smoking later in life, she said. But "because of their lower quit rates, their prevalence of smoking is higher." Also, they smoke more menthol cigarettes, which have higher levels of tar than the nonmentholated kind.
"On top of that, there is a race effect," Dr. Arora noted. "African Americans are 1.8 times more susceptible than whites to developing small cell lung cancer with the same amount of smoking."
Dr. Arora reported that she did not have any relevant financial conflicts.