Cancer registries throughout the country keep records of the number of new cancers diagnosed in their area. Ten population-based registries report this information to the NCI's Surveillance, Epidemiology, and End Results (SEER) Program. The standard time between a cancer diagnosis and its initial inclusion in cancer incidence statistics is about 2 years. However, longer delays in the reporting of the data can lead to an underestimation of cancer incidence whereas reporting errors may contribute to an overestimation of cancer incidence for the cancer sites examined. The net effects of these corrections on cancer incidence would increase in cancer incidence rates for more current diagnosis years.
Limin X. Clegg, Ph.D., of the National Cancer Institute, and colleagues recalculated cancer incidence rates from SEER data from 1981 through 1998 using statistical models that could predict additions and deletions to the data. They looked at the incidence rates of breast cancer, colorectal cancer, lung/bronchus cancer, prostate cancer, and melanoma. The authors note that the percentage change between reporting-adjusted and unadjusted cancer incidence rates for 1998 ranged from 3% for colorectal cancer (regardless of race or sex) to 14% for melanoma (regardless of sex) and for prostate cancer in black males. Prior years have smaller corrections.
They found that it would take 4 to 17 years for 99% or more of the cancer cases to be reported. In the worst case, melanoma, the number of cancers reported after the 2-year standard delay represented only 88% of the final number of cancers for that diagnosis year.
They point out that the adjusted data may also affect perceived cancer trends, particularly for selected cancers and the most recent period. For example, the unadjusted data showed a downward trend in melanoma in white males after 1997, but the adjusted data revealed a continued increase in the disease after 1980.
"Reporting adjusted cancer incidence rates are valuable in reporting better and more precise current incidence rates and trends and monitoring the timeliness of data collection. Ignoring reporting delay and reporting errors may produce downwardly biased cancer incidence trends, particularly in the most recent diagnosis years," the authors conclude.
They add that having the best possible estimate of cancer incidence is important to help quantify the relationship between changes in medical practice and its impact on cancer incidence trends.
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Clegg L, Feuer E, Midthune D, Fay M, Hankey B. Impact of reporting delay and reporting error on cancer incidence rates and trends. J Natl Cancer Inst 2002;94:1537-45.
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