Nigeria may be experiencing an increase in cancer incidence. Unfortunately, official cancer statistics for much of Africa are imputed based on the neighboring countries on the continent. It is therefore currently almost impossible to know whether local rates of cancer vary in time or compared to different populations. Like other countries, Nigeria has many cancer registries, but their data has not been of sufficient quality for inclusion in the International Agency for Research on Cancer's (IARC) Cancer in Five Continents since 1969. In collaboration with the Institute for Human Virology, Nigeria and 12 of Nigeria's cancer registries, we have completed a multi-component descriptive study that examines: (1) the extent of age heaping in the population and in cancer registries and its effect on cancer rate estimations, (2) the comparability and diagnostic validity of registryprocedures and (3) registry case completeness using IARC quality metrics. Three registries did not use international cancer coding systems; these were recoded by a cancer registrar in the United States.
We found evidence of severe age heaping which was more pronounced in the north than the south, but which did not lead to important differences in estimations of age standardized cancer rates. Across registries, procedures and recording practices were largely comparable with some exceptions. With one exception, registries had high rates of morphological verification of diagnoses. The number of case records with errors varied widely among registries; this may be due to software data management challenges or recoding errors. Lastly, in examining children's age specific incidences, we discovered evidence of incompleteness for some registries, but also higher than expected rates in other registries due to either real increased incidence of cancer in children (in particular Burkitt's Lymphoma) or referral bias and geographic-heaping. Considering the intra-country completeness comparisons, we found potential evidence of cancer specific general incompleteness as well as what appears to be incompleteness due to inability to diagnose specific cancers. Overall, Nigeria has a strong foundation in cancer registration which can be strengthened through the adoption of alternate address recording procedures. Future extensions of this work include studying rates of Burkitt's Lymphoma in children and examining the effect of age heaping on different population and disease distributions.