Socioeconomic inequalities in incidence of lung and upper aero-digestive tract cancer by age, tumour subtype and sex: a population-based study in Scotland (2000-2007)

Abstract

Background: Lung and upper aero-digestive tract (UADT) cancer risk is associated with socioeconomic inequality (SEI) but the degree of socioeconomic burden by age, tumour subtype, and sex is not known.

Methods: We reviewed 216,305 cases excluding non melanoma skin cancer (All Cancer) comprising 37,274 lung; 8216 head and neck; and 6534 oesophageal cancers from 2000 to 2007 classified into anatomical or morphology subtypes. Deprivation was measured using the Scottish Index of Multiple Deprivation and SEI was measured using the Slope Index of Inequality and the Relative Index of Inequality (RII). Analyses were partitioned by 5-year age group and sex. RII was adapted to rank tumour type contribution to All Cancer SEI and to examine subtype by age and sex simultaneously. Rank was defined as proportion of All Cancer SEI.

Results: All Cancer SEI was greater for males (RII=0.366; female RII=0.279); the combination of lung and UADT SEI contributed 91% and 81% respectively to All Cancer SEI. For both sexes lung and UADT subtypes showed significant SEI (P<0.001) except oesophageal adenocarcinoma in males (P=0.193); for females, SEI was borderline significant (P=0.048). Although RII rank differed by sex, all lung and larynx subtypes contributed most to All Cancer SEI with RII rank for oral cavity, oesophagus-squamous cell, and oropharynx following. For males 40-44 years, SEI increased abruptly peaking at 55-59 years. For females, SEI gradually peaked 10 years later. In both sexes, the SEI peak preceded peak incidence.

Conclusion: SEI in lung and UADT cancers vary greatly by age, tumour subtype and sex; these variations are likely to largely reflect differences between the sexes in risk behaviours which vary by birth cohort and are socioeconomically patterned.