Do all lung adenocarcinomas follow a stepwise progression?

Area of Science:

• Oncology
• Molecular Biology
• Genetics

Background:

• Lung adenocarcinoma was traditionally thought to follow a linear progression from precursor lesions to invasive cancer.
• Recent evidence suggests lung adenocarcinoma is a heterogeneous group of tumors arising from distinct molecular pathways.

Purpose of the Study:

• To review evidence challenging the linear progression model of lung adenocarcinoma.
• To propose a novel, non-linear scenario for lung adenocarcinoma development.

Main Methods:

• Review of molecular classification studies based on gene expression profiling.
• Analysis of mutation rates of specific genes (e.g., KRAS) across progression stages.
• Comparative genomic hybridization analysis of adenocarcinoma in situ and invasive adenocarcinoma.
• Evaluation of clinical observations regarding tumor progression.

Main Results:

• Molecular classification divides lung cancer into subsets, with linear progression potentially applicable to only one subset.
• Disproportionate distribution of KRAS mutations contradicts expected even accumulation along a linear progression.
• Comparative genomic hybridization revealed gene alterations in adenocarcinoma in situ that were discontinuous with invasive adenocarcinoma.
• Clinical observations suggest some lesions may bypass or escape linear progression.

Conclusions:

• The linear progression model may not universally apply to all lung adenocarcinomas.
• Lung adenocarcinoma development likely involves diverse and non-linear pathways.
• A novel scenario for lung adenocarcinoma progression that accounts for molecular heterogeneity is proposed.