Key message:
SCLC incidence trends are similar to those in all lung cancer. However, the decrease in the incidence of SCLC is slightly more pronounced. This decline probably reflects the reduction in smoking rates over the study period.
Trends in incidence of small cell lung cancer and all lung cancers
Background
The incidence of small cell lung cancer (SCLC) is often quoted as around 20% of all lung cancers and its incidence is reportedly decreasing over time. It is the form of lung cancer most strongly related to tobacco smoking.
Aim
We analysed the trends in incidence of SCLC and compared these with the trends in all lung cancer overall among males and females in South East England between 1970 and 2007.
Results
Incidence rates of SCLC and all lung cancer were higher in males than females (Figure 1). Among males, the incidence rates of lung cancer declined from 1972. In contrast, the incidence rates of lung cancer among females steadily increased from 1972 and appeared to remain stable from 1987 onwards. There was a decrease of SCLC incidence over time. This decrease was more rapid in the most recent years.
Overall, SCLC proportions in males increased from 9% in 1972 to 10% in 2007 (Table 1). In contrast, the proportion of females with SCLC decreased from 13% in 1972 to 11% in 2007 (Table 2). However, a large proportion of lung cancers were histologically unspecified. When we limited our analysis to lung cancer with specified histology only, we found the proportion of SCLC to decline in both males (21% in 1972 to 15% in 2007) and females (32% in 1972 to 17% in 2007).
Figure 1. Age-standardised incidence rates of all lung cancer (A and B) and SCLC (C and D) by calendar period (A and C) and birth cohort (B and D)
Methods
We identified 237,810 patients diagnosed with lung cancer (ICD-10 C33-C34) between 1970 and 2007. We computed age-standardised incidence rates using the European standard population by 5-year periods indicated by their midpoint. We used a Poisson regression age-cohort model to estimate the age-specific rates in the 1890 to 1960 birth cohorts. In addition, we analysed the proportion of lung cancer subtypes according to the ICD-O-3 morphology classification.
Conclusion
All lung cancer and SCLC incidence decreased over time in males and remained relatively stable in females. The slightly more rapid decrease in SCLC incidence rates compared to all lung cancer probably reflects the reduction in smoking rates over the study period.
Acknowledgement
This work is taken from the following publication: Trends in incidence of small cell lung cancer and all lung cancer. Sharma P. Riaz, Margreet Lüchtenborg, Victoria H. Coupland, James Spicer, Michael D. Peake, Henrik Møller. Lung Cancer. 2011 Sep 3. [Epub ahead of print].
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