Being diagnosed with cancer is no longer a death sentence. Thanks to advances in medicine, survival rates are on the rise. In fact, the National Cancer Institute states that the overall cancer death rate in the United States has declined since the early 1990s. But a disturbing trend concerning cancer appears to be an increase in cases among younger individuals. And this trend is worldwide.
The Birth Cohort Effect and Cancer
According to a study by researchers at Brigham and Women’s Hospital in Boston, an extensive global analysis of available studies and data shows a pattern of cancer called the birth cohort effect. Starting in 1990, each group (cohort) of people born 10 years later than another cohort shows a higher risk for early-onset cancer. In other words, people born in 1960 have a higher rate of these cancers than people born in 1950 and people born in 1970 have a higher risk than those born in 1960. The researchers say this pattern will probably continue and that it is leading to a global epidemic in early-onset cancers.
Cancers that show the birth cohort effect and have been increasing at epidemic rates in people under age 50 include cancers of the thyroid, stomach, prostate, bone marrow, liver, kidney, head and neck, gall bladder, bile ducts, esophagus, endometrium, colon, rectum, and breast. Finding the early-onset cancers is important but finding the reason why the increase is happening will hopefully curb the trend. The results of the analysis are published in Nature Reviews Clinical Oncology.
Theories on the Increase of Early-Onset Cancers
The research team says the exact reason or reasons for the rise in early-onset cancers cannot be determined by their study. To answer that question, researchers will need to design long-term studies that will follow people over time, called longitudinal studies. Since cancers can take years to develop, it will be a long time before results are available. For now, the researchers say there are several possible explanations.
Some of the earlier cancers are due to better screening for cancers, causing them to be found at an earlier age. Although routine screening may have been responsible for finding some early cancers, such as breast, colorectal, or prostate cancers, most other cancers do not have screening guidelines. A more important probable cause is early-life exposures that increase cancer risk. Researchers call these exposures the exposome. The exposome includes cancer risk factors in early life and young adult years from lifestyle changes, diet changes, obesity, environmental exposures, and changes in the gut bacteria, called the microbiome.
Lifestyle changes that have contributed include less sleep and less exercise. Eight of the cancers involve the digestive system, which suggests that diet exposures play a key role. Changes in diet over 50 years include highly processed foods and foods and beverages with added sugars. This may explain other risk factors, such as obesity, a changing microbiome and type 2 diabetes. The early-onset cancer epidemic may just be part of an increasing trend of many other early-developing chronic diseases. Alcohol ingestion is another cancer risk that has increased since the 1950s.
A Future of Biobanking
The research team concludes that it will be important to do longitudinal studies in the future. These studies would start in young children and follow them through life, recording data and taking body and blood samples, called biobanking. One of the weaknesses of this study is the lack of data from developing nations. The research team plans to collaborate with international research institutes to monitor global trends in these countries. For now, people need to be aware of the increasing risk and the likely risk factors. Doctors also need to be aware to help patients avoid or control risk factors and to be more aware of possible cancer signs or symptoms in younger adults.
