Improved survival in never-smokers vs current smokers with primary adenocarcinoma of the lung

Adenocarcinoma of the lung is now the most common histologic subtype of lung cancer in the United States. To determine if there are survival differences in never-smokers and current smokers with adenocarcinoma, we conducted an analysis of lung adenocarcinomas seen at the H. Lee Moffitt Cancer Center, and looked for demographic and survival differences in the two groups.

Data were gathered through the tumor registry at the H. Lee Moffitt Cancer Center and confirmed by chart review. A total of 132 documented never-smokers and 522 current smokers with lung adenocarcinoma were included. Detailed demographic survival information were gathered and tabulated. Former smokers were not included in the study. Multivariate analyses were performed using the Cox regression method to identify variables with independent prognostic significance. Life table actuarial analyses were performed to determine survival. Differences between survival curves were estimated using the log-rank test.

The mean age at diagnosis for never-smokers was higher as compared to current smokers: 63.5 years vs 59.4 years (p = 0.0005). In addition, there was an increased percentage of female subjects in the never-smoker category: 78% vs 54% (p < 0.0001). There was a statistically significant difference in survival between current smokers and never-smokers (p = 0.004). The Kaplan-Meier estimates at 5 years were 16% for current smokers and 23% for never-smokers. On multivariate analyses, smoking was identified as an independent negative prognostic factor.

Our data show that never-smokers with adenocarcinoma are predominantly female, present at a higher mean age, and have improved survival when compared to current smokers. By multivariate analyses, the never-smoking status was found to be an independent predictor of improved survival. The survival difference may be partly influenced by less comorbidity among never-smokers. Nevertheless, owing to differences in the mechanism of carcinogenesis (in smokers vs nonsmokers), demographic factors, tumor behavior and survival, adenocarcinomas occurring in never-smokers may display a distinct natural history and may warrant further investigation as a separate entity with epidemiologic studies and clinical trials designed specifically for this category of non-small cell lung cancer.