Significant Differences for Age of Diagnosis Between Blacks and Whites for Six Types of Cancer
Although blacks were diagnosed at younger ages than whites for nearly every cancer type, after adjustments for population structure shifted the comparisons toward older ages among blacks, only six statistically significant differences of 3 or more years remained, according to a study reported by Robbins et al in the Journal of the National Cancer Institute.
Blacks were 10.2 years younger than whites at diagnosis for Kaposi sarcoma, 5.6 years younger for male soft-tissue cancer, 5.5 years younger for male anal cancer, and 3.7 years younger for non-Hodgkin lymphoma. Blacks were 4.7 years older than whites at diagnosis for cervical cancer and 3.3 years older for female thyroid cancer.
“Smaller differences (< 3 years) were present for female breast, female colon, lung, pancreas, prostate, and uterine corpus cancers (all P ≤ .001),” reported researchers from the National Cancer Institute, Division of Cancer Epidemiology and Genetics, Rockville, Maryland, and the Department of Epidemiology at Johns Hopkins Bloomberg School of Public Health in Baltimore.
Population Distribution in SEER Data Older for Whites
Using Surveillance, Epidemiology, and End Results (SEER) data for non-Hispanic blacks and non-Hispanic whites from 18 regions for the year 2010, the investigators “calculated crude mean ages at diagnosis among cases of 29 cancer types for whites and blacks. Separately, we calculated adjusted means that corrected for differences in population structure, which we obtained by fitting linear regression models to the ages at diagnosis with statistical weights specific to age and sex,” the authors explained.
The population distribution in the SEER data was older for whites than blacks. “Individuals older than age 50 years made up 23.2% and 34.7% of the population for blacks and whites, respectively, and individuals older than age 70 years made up 4.2% and 8.1%, respectively. The mean age among blacks was 33 years, compared with 39 years for whites,” the authors reported.
Most Differences Were Small
Among 29 cancer types included in the analysis, “a statistically significant (P < .10) interaction between sex and race was present for esophageal, colon, anal, soft-tissue, and thyroid cancers,” the researchers stated, and analyses for these cancers were stratified by sex. This resulted in 34 comparisons and in 32 of those the crude mean age at cancer diagnosis was younger in blacks than in whites, with differences ranging from 13.3 years younger for blacks diagnosed with Kaposi sarcoma to 1.3 years older for cervical cancer.
“After adjusting for differences in population structure between blacks and whites, the apparently younger mean age for blacks was greatly diminished for most cancers, and for a few cancers adjustment for population structure revealed older ages in blacks that were previously masked,” the researchers stated. Adjusted mean differences ranged from 10.2 years younger for blacks diagnosed with Kaposi sarcoma to 4.7 years older for cervical cancer.
“Most differences between blacks and whites in the age at cancer diagnosis are small,” the investigators concluded. “Large differences for a few cancer types may be driven by etiologic and subtype heterogeneity as well as disparities in access to care.”
Hilary A. Robbins, MSPH, of the Johns Hopkins Bloomberg School of Public Health, is the corresponding author for the Journal of the National Cancer Institute article.
The study was supported by the Intramural Research Program of the National Cancer Institute at the National Institutes of Health.
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