Data quality in rare cancers registration: the report of the RARECARE data quality study.

Purpose: Rare cancers represent 22% of all tumors in Europe; however, the quality of the data of rare cancers may not be as good as the quality of data for common cancer. The project surveillance of rare cancers in Europe (RARECARE) had, among others, the objective of assessing rare cancer data quality in population-based cancer registries (CRs). Eight rare cancers were considered: mesothelioma, liver angiosarcoma, sarcomas, tumors of oral cavity, CNS tumors, germ cell tumors, leukemia, and malignant digestive endocrine tumors.
Methods: We selected data on 18,000 diagnoses and revised, on the basis of the pathologic and clinical reports (but not on pathologic specimens), unspecified morphology and topography codes originally attributed by CR officers and checked the quality of follow-up of long-term survivors of poor prognosis cancers.
Results: A total of 38 CRs contributed from 13 European countries. The majority of unspecified morphology and topography cases were confirmed as unspecified. The few unspecified cases that, after the review, changed to a more specific diagnosis increased the incidence of the common cancer histotypes. For example, 11% of the oral cavity epithelial cancers were reclassified from unspecified to more specific diagnoses: 8% were reclassified as squamous cell carcinoma (commoner) and only 1% as adenocarcinoma (rarer). The revision confirmed the majority of long-term survivors revealing a relative high proportion of mesothelioma long-term survivors. The majority of appendix carcinoids changed behavior from malignant to borderline lesions.
Conclusions: Our study suggests that the problem of poorly specified morphology and topography cases is mainly one of difficulty in reaching a precise diagnosis. The awareness of the importance of data quality for rare cancers should increase among registrars, pathologists, and clinicians.