Some aspects on validity of breast cancer, pancreatic cancer and lung cancer registration in Swedish official statistics.

From the Regional Cancer Register of Stockholm County and the Swedish Cause-of-Death Register, a total of 1445 individuals were selected. The patients had died in 1978 and were recorded with cancer of breast, pancreas or lung in either (or both) register. Inter-register discordance in regard to diagnostic information was found in 411 cases. Clinical records were retrospectively studied in order to establish the correct diagnosis. In breast cancer, most of the discordance was explained by the numerous deaths from intercurrent causes, though some underestimation of breast cancer as cause of death was noted (5%). Several incorrect entries of pancreas and lung cancer were found in the Cause-of-Death Register, due to inclusion of metastatic disease as primary tumour or non-alteration of the death certificate when a subsequent autopsy showed another diagnosis. In the Cancer Register, few diagnoses of pancreas and lung cancer were found to be incorrect. On the other hand, the register showed a slight undernotification of these tumour types. Routine alteration of death certificates when autopsy gives results differing from the clinical diagnosis and information to doctors concerning the aims, routines and coding procedures at the Cancer and Cause-of-Death Registries, presumably would enhance the accuracy of the registers' statistics.