Incompleteness of oral cancer registration in south-east England, 1971-87.

Our objective was to examine the accuracy of reporting oral cancer cases to the cancer registry system. We examined a series of 583 patients with oral malignancies treated at several institutions and reported by our laboratory during 1971-87. Using patient details and pathology diagnosis, we traced the entries for these patients in the Thames Cancer Registry (TCR). Of the 583 patients identified 351 were eligible for entry in TCR. Of these, 255 were traced in the Registry and 96 were not (27%). The data, when separated for the period 1971-80 and post-1980, showed that for the earlier period under-reporting was 21% and for the later period 36%: Underascertainment was particularly marked in the mid-1980s while regional registration in the North Thames Regions was being discontinued and taken over by TCR. The major factors contributing to under-reporting are thought to be the fact that many specialised dental units and oral pathology laboratories may fail to be included in the cancer registration process and possible inconsistencies in death-initiated registrations related to this site. Similar levels of under-reporting were observed in another regional registry (South Western), suggesting that this may be a national problem. If this is the case, national incidence rates for mouth cancer may have been underestimated by about 25% during this period. This contrasts with over 90% completeness of registration for cancers as a whole.