Time to first cigarette independently predicts lung cancer

By Joanna Lyford, Senior medwireNews Reporter

The time to first cigarette after waking (TTFC) is an independent risk factor for lung cancer, a Japanese case-control study has found.

Analysis of more than 3000 individuals found that TTFC, a marker of nicotine dependence, was associated with both adenocarcinoma and squamous/small-cell carcinoma, with the strength of association varying by histologic subtype.

Researchers led by Keitaro Matsuo (Kyushu University, Fukuoka, Japan) used a hospital database to identify 1572 patients diagnosed with lung cancer between 2001 and 2005 and 1572 cancer-free individuals (controls) matched by age and gender.

In all, 903 cases and 1143 controls were ever-smokers. Patients with cancer were more likely than controls to be current smokers, smoked more cigarettes per day, and had smoked for a longer duration. Compared with controls, cases had a lower intake of fruit and vegetables and were more likely to work in unskilled or manual occupations.

After adjusting for these baseline differences, TTFC significantly inversely correlated with lung cancer risk. Using never-smokers as the reference, adjusted odds ratios (ORs) for lung cancer were 1.15, 1.63, 2.42, and 2.76 for TTFC of more than 60 minutes, 31–60 minutes, 6–30 minutes, and 5 minutes or under, respectively, in former smokers and 1.65, 2.67, 4.05, and 6.57, respectively, in current smokers.

Analysis by histologic subtype found a similar pattern of correlation in both adenocarcinoma and squamous/small-cell carcinoma, but with larger ORs in the latter. This might be explained by different exposure of tobacco smoke particles to sites that are more peripheral in the respiratory tract, say the authors.

“Compared with [adenocarcinoma] located in the peripheral sections of the lung, [squamous/small-cell carcinoma] occurs mainly in the large central bronchi, an area highly exposed to large particles from tobacco smoking,” write Matsuo et al in the Annals of Oncology.

Finally, the authors found a significant negative correlation between the number of cigarettes smoked per day and TTFC, suggesting that TTFC is not merely a marker of nicotine dependence but also of tobacco exposure.

They conclude: “[O]ur findings and previous observations suggest that TTFC is an indicator of tobacco dependence impacting on cancer risk that is not adequately measured by the other aspects of smoking, which is supported by evidence that TTFC is highly correlated with the cotinine level and in turn, the cotinine level correlates with tobacco-related carcinogens.”

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