According to results of a large observational study examining the incidence of 30 types of invasive cancer diagnosed in adults aged 25-84 years (grouped by 5-year increments), the incidence of 6 of the 12 established obesity–related cancers studied increased in a stepwise manner in adults aged 25-49 years from 1995 to 2014, with the youngest age groups showing the steepest rises in incidence for these cancers. This study was published online in Lancet Public Health.1
Risk factors for cancer development in younger adults are less well understood compared with cancers in older adults. In this study, the authors speculated that early- and long-term exposure to carcinogens, such as excess adiposity, may influence an individual’s cancer risk, particularly for certain cancers linked to obesity.
The researchers chose to limit their analyses to 30 types of cancer diagnosed over a 20-year period (in 4 time-period increments including 1995–1999, 2000–2004, 2005–2009 and 2010–2014), during which obesity rates in childhood and adolescence increased dramatically over time for adults in the younger groups compared with the older age groups. They mined 25 US state cancer registries that had data on invasive cancer rates from 1995–2014 for the analysis.
“This study is the first, to our knowledge, to systematically examine the contemporary incidence trends for 12 obesity-related cancers and 18 additional cancers in young adults in the USA with nationally representative population-based data,” the authors wrote.1
The 12 obesity related-cancer types selected were: colorectal cancer; esophageal adenocarcinoma; gallbladder cancer; cancer of the gastric cardia; kidney cancer; liver and intrahepatic bile duct cancer; multiple myeloma; pancreatic cancer; thyroid cancer; cancer of the uterine corpus; breast cancer; and ovarian cancer. The other 18 cancer types were chosen based on their relatively high incidence in the 25–49 year-old age group. These included cancers of the anus, brain, CNS, cervix, esophagus (squamous cell carcinoma), stomach (noncardia gastric), larynx, lung and bronchus, oropharynx, prostate, testes, urinary bladder, and vulva, as well as Kaposi sarcoma, leukemia, lymphoma (Hodgkin and non-Hodgkin), and skin melanoma. Overall, 14,672,409 cases representing the 30 types of cancer were identified.
During the period from 1995 to 2014, the incidence of multiple myeloma and cancers of the colorectum, uterine corpus, gallbladder, kidney, and pancreas increased in younger adults (aged 25-49 years). Smaller increases in incidence were also observed for older adults with these cancers, with the exception of colorectal cancer.
Notably, for these 6 cancers, the younger the age group, the greater the magnitude of the increase. For example, while the average annual percent change in incidence of pancreatic cancer was <1% for those aged 40 to 84 years, it was 1.3%, 2.5%, and 4.3% for those aged 35–39 years, 30–34 years, and 25–29 years, respectively. Nevertheless, the authors noted that the overall incidence of these cancers is higher in older age groups compared with younger age groups. Of the other 18 cancers not designated as being related to obesity, only 2 (noncardia gastric cancer and leukemia) showed increases in incidence with decreasing patient age.
The authors stressed that these “findings can help establish hypotheses about the relationship between the obesity epidemic and early-onset cancer, but do not provide information for a causal relationship.”1
An accompanying editorial article, while noting the “timely insights” of this study, raised questions regarding the evidence related to obesity in the 18 cancer types classified as non-obesity-related, the rationale for grouping certain cancer subtypes together (such as all non-Hodgkin lymphomas and all lung cancers), and the lack of an association with younger age and increased incidence in the other 6 cancers classified as obesity-related.2
Despite their concerns, the authors of the editorial still agreed that “the findings suggest the need for further close epidemiological monitoring of cancer incidence trends in younger adults and highlight the need for rigorous etiological studies of exposures that could be responsible for the trends.”2
- Sung H, Siegel RL, Rosenberg PS, Jemal A. Emerging cancer trends among young adults in the USA: analysis of a population-based cancer registry [published online February 4, 2019]. Lancet Public Health. doi: 10.1016/S2468-2667(18)30267-6
- Marinac CR, Binmann BM. Rising cancer incidence in younger adults: is obesity to blame? [published online February 4, 2019]. Lancet Public Health. doi: 10.1016/S2468-2667(18)30267-6.v