Although blacks were diagnosed at a younger age 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 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 and Johns Hopkins Bloomberg School of Public Health.
Using Surveillance, Epidemiology, and End Results (SEER) data for non-Hispanic blacks and 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.
Among 29 cancer types included in the analysis, “a statistically significant (P < .10) interaction between gender and race was present for esophageal, colon, anal, soft-tissue, and thyroid cancers,” the researchers stated, and analyses for these cancers were stratified by gender. This resulted in 34 comparisons, and in 32 of them, 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 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.” ■
Robbins HA, et al: J Natl Cancer Inst 107:dju489, 2015.