The commonest type of lung carcinoma in nonsmokers is -
"Adenocarcinoma is the most common type of lung cancer in women and nonsmokers". — Robbin's
Predisposing factors for lung cancer

A smoking → Most important factor associated with lung carcinoma. Two lung cancer cell types, squamous cell carcinoma and small cell carcinoma are strongly associated with cigarette smoking and are extremely rare in the absence of cigarette smoking.
High dose ionizing radiation eg. by uranium
Asbestos exposure
Radon exposure
Contact with certain chemicals and substances: such as uranium, chromium and nickel; can cause lung cancer, but this is rare.
Molecular genetics → All the previously mentioned factors cause a genetic alteration in lung cells, which accumulate and eventually lead to the neoplastic phenotype.

- Small cell cancer → Alteration in c-MYC & RB genes.
- Non-small cell cancer → Alteration in RAS & p16 genes.
- Both small and non-small cancer → p53 gene
- Squamous cell carcinomas show the highest frequency of p53 mutations.
- K-RAS mutations are seen primarily in adenocarcinoma.
- In small cell cancer, there is a high expression of the anti-apoptotic gene BCL 2 and low expression of the pro-apoptotic gene BAX.
Squamous cell CA
Small cell CA
Adeno CA
Alveolar cell CA