One can begin by seeing their family doctor (general practitioner) who can examine and arrange for tests or x-rays to check for any abnormalities in the lungs. 

Sputum Cytology:

Samples of phlegm can be examined under a microscope for cancer cells. 

CT Scan:

This special x-ray can detect very small lung lesion and its spread to adjacent organs.

Bronchoscopy:

In this test the inside of the lung airways is examined and cell samples (called biopsies) are taken. A thin, flexible tube called a bronchoscope is used, and the test is carried out using local anaesthesia. When a rigid bronchoscope is used general anaesthetic is given. 

Before bronchoscopy one will be asked not to eat or drink anything for a few hours. Just before the test a mild sedative will be given to help relax and relieve any discomfort.Another medicine to reduce the secretions will also be given. This medicine can make one's mouth feel rather dry. Once comfortable a local anaesthetic will be sprayed onto the back of the throat and The bronchoscope is then gently passed through the nose or mouth and into the lung airways. The doctor can look through the bronchoscope to check for any abnormalities. Photographs and cell samples can be taken at the same time. The test may be slightly uncomfortable but it only takes a few minutes.

Lung Biopsy:

A biopsy is a test in which tissue is removed from the suspected tumor and looked at under a microscope to see if cancer cells are present. This may be done by inserting a needle through the chest wall to take a sample of tissue from a known tumor, or it may involve surgery in which the doctor opens the chest wall to remove a part or all of the tumor. A biopsy is necessary for the doctor to confirm a cancer diagnosis and to identify the specific type of cancer. Special staining technique maybe used for this purpose.