METHODS
Study participants
Cases were patients with confirmed lung cancer aged f55 yrs at the time of diagnosis, identified from hospital databases and the New Zealand Cancer Registry between January 2001 and July 2005. Hospital databases were also used because a few clinical-only diagnoses of lung cancer are not received by the Cancer Registry [24]. Cases were a mixture of prevalent and incident cases of lung cancer. Subjects were excluded if they had lung metastasis from a distant primary site other than lung, or a histological diagnosis of carcinoid or melanoma. Age at diagnosis, anatomical location of their malignancy and histological type were collected for cases. Controls without lung cancer were randomly selected from the electoral roll and frequency matched in 5-yr age groups and district health boards. Subjects came from eight district health board regions, serving both urban and rural populations. The eight districthealth boards serve together ,1.8 million people, representing just under one-half of the total New Zealand population. The present study was approved by the regional ethics committees and each participant gave written informed consent. Patients with cancer of the head and neck were also interviewed, but will be reported separately.