The goal of this multicentric French randomized trial is to determine the best auto fluorescence bronchial endoscopic follow-up strategy in high risk patients bearing low grade bronchial precancerous lesions. This Trial compares two follow-up modalities : observation without endoscopy for a three year period (group A " light " follow-up), versus repeated autofluorescence endoscopies and biopsies every six months for three years (group B " intensive "). Methods: 300 subjects at high risk for lung cancer will be included over a two year period and followed-up for three years. In each subject an auto-fluorescence endoscopy and a Chest CT scan will be performed before the enrollment into the trial. To be included the subject must present with an initial Chest CT scan not suspicious for lung cancer and bronchial biopsy showing a moderate dysplasia or a lower grade lesion.

Subjects will be randomly assigned to one of the following arm :

(A) every 6 months clinical and chest Xrays follow-up without intermediate endoscopy, (B) every 6 months clinical and chest Xrays follow-up including repeated autofluorescence endoscopy and biopsies on a 6 months basis in case of low grade dysplasia or on a one year basis in patients without dysplasia. Stratifications factors for randomization are: Center, occupational exposure to respiratory carcinogens, presence of a bronchial low dysplastic lesion versus absence of dysplasia. Bronchial biopsies samples will be centrally reviewed by a panel of Pathologists.

After 36 months follow-up, each patient from the two groups will be subjected to a final autofluorescence endoscopy and biopsy and a Spiral Chest Xray.

The final analysis will compare between the two groups :

1. The probability of progression from an initially identified low grade lesion to a high grade lesion
2. The probability of respiratory epithelial tract progression assessed by the occurrence of a lung cancer or high grade lesion.
3. The characteristics of lung cancers detected in each arm
4. In both arm, the influence of risk factors and persistent exposure to tobacco on lesion evolutivity.

First inclusion into the trial : July 2002, End of recruitment December 2005, End of follow- up : december 2008.

An ancillary study analysing the performances of fibered confocal fluorescence microscopy has been started in december 2005 after IRB/ethical comity approval. This ancillary study is only performed at the Rouen University Hospital Center.