Comparability, diagnostic validity and completeness of Nigerian cancer registries

Background: Like many countries in Africa, Nigeria is improving the quality and coverage of its cancer surveillance. This work is essential to address this growing category of chronic diseases, but is made difficult by economic, geographic and other challenges. Purpose: To evaluate the completeness, comparability and diagnostic validity of Nigeria's cancer registries. Methods: Completeness was measured using children's age-specific incidence (ASI) and an established metric based on a modified Poisson distribution with regional comparisons. We used a registry questionnaire as well as percentages of death-certificate-only cases, morphologically verified cases, and case registration errors to examine comparability and diagnostic validity. Results: Among the children's results, we found that over half of all cancers were non-Hodgkin lymphoma. There was also evidence of incompleteness. Considering the regional 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. We found that registration was generally comparable, with some exceptions. Since autopsies are not common across Nigeria, coding for both them and death-certificate-only cases was also rare. With one exception, registries in our study had high rates of morphological verification of female breast, cervical and prostate cancers. Conclusions: Nigeria's registration procedures were generally comparable to each other and to international standards, and we found high rates of morphological verification, suggesting high diagnostic validity. There was, however, evidence of incompleteness.