The 11 Cancer Types Increasing Most Often in Young Adults and Why

Why Is Cancer Increasing in Young Adults? BMJ Oncology's Data from England and the Quiet Rise of Obesity

This report provides a scientific framework for a series of headlines that have stirred public concern in recent months — "colon cancer cases are increasing among people in their 30s" and "breast cancer in women is becoming more common before 40". Nor is this solely an issue in England. Similar patterns are being observed in US national cancer registries, Australia, Canada and many European countries. Its significance is also growing in Türkiye and across the OECD — particularly, as the journal and ICR spokespeople emphasise: obesity screening programmes will shape the cancer burden of the next two decades.

Data Size and Scope

The Cancer Epidemiology and Prevention Research Unit (CEPRU) team at the ICR used data from England's national cancer registry to analyse an 18-year window between 2001 and 2019 covering the incidence of 22 cancer types in women and 21 in men. The age group studied was defined as 20-49 years — the range recognised in the literature as "early-onset cancer". For comparison, trends in the same cancer types were also examined in the over 50 age group.

The study independently modelled trends in traditional behavioural risk factors — smoking, alcohol, physical inactivity, red/processed meat, low fibre intake and body mass index (BMI) — over the past two decades. If a factor is stable or declining, it cannot explain the increase in cancer on its own; if it is rising, the researchers look for a pattern that aligns with the increase in cancer.

Expected and Unexpected Findings

Almost all of the 11 cancers increasing in young adults (apart from oral cancer) are known to be associated with excess weight . Most are also increasing in parallel in the over 50 age group — so the problem is not specific to young people; it is a population-wide trend that has also become evident in the younger segment. But two cancer types stand out: colon cancer and ovarian cancer are increasing only in the younger age group, while remaining stable or declining in older people. This is particularly striking because it strengthens the cohort-effect hypothesis: a biologically different exposure profile among people born after 1975.

Among young women, the rate of BMI-associated colon cancer increased from 0.9 to 1.6 per 100,000 over 18 years. Over the same period, colon cancer not attributable to BMI rose from 6.4 to 9.6 per 100,000. A similar pattern is seen in men. The subtle point here is that the number of colon cancer cases attributable to BMI remains lower in absolute terms; excess weight therefore cannot fully explain this increase. Other factors must also be involved.

Smoking Declined and Alcohol Was Stable — Yet Cancer Is Increasing

The study's most surprising finding is that the behavioural risk factors expected to rise alongside cancer have instead declined. Among young adults in England, smoking has decreased by 2% annually over the past two decades. Alcohol consumption has largely been stable or declining. Physical activity has increased, red and processed meat consumption has fallen, and fibre intake has risen slowly but significantly. In other words, the effects of public health campaigns are observable.

Even so, the authors themselves acknowledge: obesity alone cannot fully explain this increase in cancer. Calculations show that, between 2001-2019, approximately 20% of the increase in colon cancer among young adults can be explained by rising BMI; that leaves 80%. Excess weight is therefore our strongest clue, but not the only culprit.

More Than Weight — Insulin, Inflammation and the Microbiome

Why obesity increases cancer risk has been one of the most productive areas of research over the past two decades. Obesity involves at least 19 distinct mechanisms linked to different cancer types. During press briefings, Marc Gunter, who worked on the ICR and Imperial team's study, particularly highlighted the role of insulin . In people with obesity, blood insulin levels remain chronically elevated; insulin is a growth factor and stimulates cell proliferation. In people with obesity, a direct link between early-onset colon cancer and high insulin levels has been demonstrated in recent research. In addition:

These mechanisms tell us that: BMI is the accepted measure of obesity, but it does not capture all of its biology. Waist circumference, the proportion of visceral fat, the presence of NAFLD/MASH, insulin resistance scores (HOMA-IR) and markers of chronic inflammation (CRP, IL-6) all add risk independently of BMI. So when the study's authors say that "rising BMI does not fully explain the increase in cancer", they are, in effect, saying that "obesity-related factors that BMI does not capture probably also play a role".

The Microbiome, Ultra-Processed Foods, Antibiotics and Air Pollution

For the unexplained 80%, the study points to a series of factors that are suspected but not yet proven . Particularly notable among them are:

An important point emphasised by the authors is that many of these suspected factors have themselves been stable or declining in England (antibiotic use, for example), making it difficult for these factors, too, to explain the increase in cancer on their own. The situation we face is therefore: the major known culprits do not explain the rise in cancer; obesity alone is not enough either; what remains is biology that we have yet to define fully.

What Do the Data from Türkiye Show?

Although this study uses data from England, it has direct and critical implications for Türkiye. Over the past two decades, Türkiye has been among the OECD countries with the fastest growth in obesity prevalence. The multicentre OBREDI-TR study, published in 2024, described adults with BMI ≥30 kg/m² at 28 centres across seven different regions of the country. Adult obesity prevalence in Türkiye exceeded 30% among women; an increase of up to 4 times was reported in children and adolescents. This parallels the global surge in adolescent obesity.

According to the OECD's 2025 report, the burden of non-communicable diseases in Türkiye is expected to grow almost twice as fast as the OECD average in the coming years. Three main forces drive this projection: population ageing, intensifying non-smoking exposures (air pollution, ultra-processed food and physical inactivity), and the rapid pace of the obesity epidemic. Young people in Türkiye start with a lower prevalence of smoking than their peers in England — but carry a greater burden of obesity and metabolic syndrome.

Being "Young" Can No Longer Be Considered Protection from Risk

In practice, the study conveys the following messages:

What Are the Limits of This Study?

To assess the value of this BMJ Oncology analysis appropriately, its limitations must also be understood:

This article is for medical news and information purposes and does not provide individual treatment guidance. People with cancer symptoms at a young age or a family history are advised to consult the relevant medical oncology specialist for evaluation. Editor's note: The article is based on the ICR and Imperial College London press releases of 28 April 2026 and the study published in BMJ Oncology; OBREDI-TR and OECD sources were used for the context in Türkiye.