We modeled temporal trends in the 1-and 5-year survival of 32 499 patients with adenocarcinoma and squamous cell carcinoma of the lung in the Swedish Cancer Register between 1961 and 2000. The 1-year relative survival for adenocarcinoma improved from 37% for patients diagnosed 1961 -1965 to 45% for those diagnosed 1996 -2000 and from 39 to 45% for squamous cell carcinoma. The adjusted excess mortality ratios for the period 1996 -2000 compared with 1961 -1965 were 0.80 for adenocarcinoma and 0.81 for squamous cell carcinoma. Thus, a previous report in a Dutch study of a relatively worsening prognosis for adenocarcinoma over time could not be confirmed. Over the past three decades in many Western countries, there has been a relative increase in the incidence of adenocarcinoma of the lung compared with other histological types 2003). The same phenomenon has been observed in Sweden, particularly among men (Myrdal et al, 2001). This shift cannot be attributed simply to changes in classification or diagnostic methods (Charloux et al, 1997). It is more likely to reflect the increased use of lower tar and nicotine cigarettes, which are suspected of preferably favouring the development of adenocarcinoma (Wynder and Muscat, 1995; Stellman et al, 1997;Thun et al, 1997).Data from a regional population-based cancer register in the Netherlands during the period 1975 -1994 indicated not only doubling of the relative incidence of adenocarcinoma but also a decline in its relative survival, even as relative survival ratios (RSRs) remained unchanged for other forms of non-small cell lung cancer. It was hypothesised that the decreased survival was also related to increased use of lower-yield cigarettes, and suggested that among adenocarcinomas, those caused by smoking may be more aggressive than those unrelated to smoking (Janssen-Heijnen et al, 2001).We used nationwide, population-based data for Sweden over a 40-year period to investigate survival trends for adenocarcinoma compared with squamous cell carcinoma, the other main type of non-small cell lung cancer.
METHODSData for this analysis were derived from the national Swedish Cancer Register (SCR), which was established in 1958. Swedish law mandates the report of all newly diagnosed malignant tumours, as well as benign tumours from selected sites. The completeness of reporting to the SCR has been very high throughout its existence; in 1975, it was estimated that almost 100% of all malignant tumours were reported (National Board of Health and Welfare, 1980). The SCR uses the ICD-7 to classify primary site and the PAD code, assigned by the diagnosing pathologist, to denote the histological subtype. Approximately 97% of the cases are morphologically verified with little change over time (National Board of Health and Welfare, 1998).Criteria for inclusion in this analysis included age 20 -80, diagnosis of a malignant lung tumour (ICD-7: 162.1) between 1961 and 2000 and no prior diagnosis of cancer. Because large cell carcinoma and small cell lung cancer were combined as one catego...