Multiple studies have reported increasing rates of cancer in younger adults in individual countries, but have not included an international comparison across countries. To address this limitation, Berrington de Gonzalez et al conducted a surveillance study across 42 countries evaluating cancer incidence among younger and older adults. The study found that other than colorectal cancer, increases occurred in both age groups, and all were related to obesity, including endometrial and kidney cancers. However, some obesity-related cancers, such as stomach, esophageal, and breast cancers, decreased in younger adults. The study’s findings can help inform future research and clinical and public health guidelines. The study by Berrington de Gonzalez et al is published in Annals of Internal Medicine.

Study Methodology

The researchers analyzed data obtained from the International Agency for Research on Cancer’s GLOBOCAN Cancer Over Time database on 42 countries from 2003 to 2017. The countries included were in Asia (n = 11), Europe (n = 22), Africa (n = 1), North and South America (n = 6), and Australasia (n = 2).

They used joinpoint regression to estimate the average annual percentage change (AAPC) in cancer rates for 13 cancer types previously reported to be increasing in many countries in younger adults. The cancers included leukemia and colorectal, stomach, breast, prostate, endometrial, gallbladder, kidney, liver, esophageal, oral, pancreatic, and thyroid cancers.

The researchers defined cancer in younger adults as a diagnosis occurring between the ages of 20 and 49, and in older adults ages 50 and older.

Results

The researchers found that incidence rates increased in younger adults in most (> 75%) countries between 2003 and 2017 for 6 of the 13 cancer types, including thyroid cancer (median AAPC, 3.57%), breast cancer (median AAPC, 0.89%), colorectal cancer (median AAPC, 1.45%), kidney cancer (median AAPC, 2.21%), endometrial cancer (median AAPC, 1.66%), and leukemia (median AAPC, 0.78%).

Incidence rates for these cancer types also increased in older adults in most countries (median AAPCs, 3% for thyroid cancer, 0.86% for breast cancer, 1.65% for kidney cancer, 1.20% for endometrial cancer, and 0.61% for leukemia). The exception was colorectal cancer, which only increased in older adults in about half of the countries (median AAPC, 0.37%); the AAPC was greater in younger than older adults in 69% of countries. For liver, oral, esophageal, and stomach cancer, rates decreased in younger adults in more than half the countries.

“Cancer incidence rates increased for several cancer types in many of the countries studied. However, other than colorectal cancer, these increases occurred in both younger and older adults. These findings can help inform future research and clinical and public health guidelines,” concluded the study authors.

Amy Berrington de Gonzalez, DPhil, Professor of Clinical Epidemiology at the Institute of Cancer Research, is the corresponding author of this study.

Disclosure: Funding for this study was provided by the Institute of Cancer Research and the National Institutes of Health Intramural Research Program. For full disclosures of all study authors, visit acpjournals.org.