Histopathology of a lung cancer shows 'Clara cells' probable diagnosis is -
Bronchioloalveolar carcinoma 

It is a histological type of adenocarcinoma.
It occurs in the pulmonary parenchyma in the terminal bronchioloalveolar pattern.
The tumor is almost always in the peripheral portion of the lung.
More often it occurs as multiple diffuse nodules that sometimes coalesce to produce a pneumonia-like consolidation.
The key feature of bronchioloalveolar carcinomas is their growth along preexisting structures without destruction of the alveolar architecture. This growth pattern has been termed "lepidic" an allusion to the neoplastic cells resembling butterflies sitting on a fence.
Stromal, vascular or pleural invasion is characteristically absent.
Bronchioloalveolar carcinoma consists of mucin-secreting bronchiolar cells, Clara cells, or rarely type II pneumocytes.
These tend to have aerogenous spread and patient usually dies of suffocation (not by metastatic spread).
Bronchioloalveolar carcinoma has two subtypes -

i) Non-mucinous → Rare aerogenous spread and therefore amenable to surgical resection.
ii) Mucinous → Tend to spread aerogenously, forming satellite tumors.
Squamous cell cancer
Bronchio alveolar cancer
Large cell cancer
Papillary carcinoma