Multiple primary malignant neoplasms in England and Wales, 1971-1981.

In the period 1971-81, more than 1.9 million persons were registered with a malignant neoplasm among the 49.2 million population of England and Wales. For 63,536 people, two or more tumor registrations (multiple tumor records) have arisen in that period. Because of the structure of the National Cancer Registration scheme, some errors in registration are inevitable, particularly duplicate registration of a single tumor by adjacent regional cancer registries. A pilot study showed that 61 percent of multiple records would represent true multiple primary malignancy, and that these records could be readily separated from registration errors. After abstraction of identifying codes from each tumor, 129,047 tumors involved in 63,536 multiple records were matched to the national cancer file, and the full data set extracted for successfully matched tumors. Person-years data were extracted for the 1.8 million tumors not involved in a multiple record. Eleven percent of multiple records were not completely matched, and a further 16 percent were excluded on SEER criteria, or as probable registration errors, leaving 46,155 multiple primary tumors for further analysis. Over 3 million person-years at risk of a second tumor were accrued. The overall risk of a second tumor at any site before age 85 was 0.77 for males and 0.80 for females, after exclusion of second tumors observed within 12 months of the first. The risk of a new primary apparently decreased with increasing duration of survival, a trend which may be due in part to under-registration of second tumors in the early 1970s and an improvement in linkage since 1971.