Comparability of stage data in cancer registries in six countries: lessons from the international cancer benchmarking partnership
Abstract
The
International Cancer Benchmarking Partnership is investigating cancer
survival differences between six high-income nations using
population-based cancer registry data. Differences in overall survival
are often explained by differences in the stage at diagnosis and
stage-specific survival. Comparing stage at diagnosis using cancer
registry data is challenging because of different regional practices in
defining stage, despite the existence of international staging
classifications such as TNM. This paper describes how stage data may be
reconciled for international analysis. Population-based cancer registry
data were collected for 2.4 million adults diagnosed with colorectal,
lung, breast (women) or ovarian cancer during 1995-2007 in Australia,
Canada, Denmark, Norway, Sweden and the United Kingdom. The stage data
received were coded to a variety of international systems, including the
TNM classification, Dukes' for colorectal cancer, FIGO for ovarian
cancer, and to national 'localised, regional, distant” categorisations.
To optimise comparability for analysis, a rigorous and repeatable
process was defined to produce a final stage variable for each patient.
An algorithm was also defined to map TNM, Dukes' and FIGO to a
“localised, regional, distant” categorisation. We recommend how stage
data should be recorded and processed to optimise comparability in
population-based international comparisons of stage-specific cancer
outcomes. The process we describe to produce comparable stage data forms
a benchmark for future research. The algorithm to convert between TNM
and a “localised, regional, distant” categorisation should be valuable
for international studies, until global consensus is achieved to adhere
to a single staging system like TNM.
