With aim to collate and summarise recent epidemiological data on the incidence trends of 12 types of cancer in young adults to inform and underpin health policy and help address age-related inequalities in cancer diagnosis, a group of investigators from UK and Australia analyzed data from 98 studies that met the inclusion criteria. They found that the incidence of colorectal, breast, kidney, pancreatic, and uterine cancers is increasing in younger age groups, whilst the incidence of lung, laryngeal and bladder cancers is decreasing. Data for oesophageal, stomach, ovarian cancers and multiple myeloma were inconclusive. The findings are published in June 2022 issue of the British Journal of Cancer by dr Erika di Martino of the Division of Primary Care, Public Health & Palliative Care, Leeds Institute of Health Sciences, University of Leeds in Leeds, UK and colleagues.
The authors wrote in the study background that growing evidence suggests that younger patients with cancer are more likely to experience a diagnostic delay. As cancer is more common in the elderly, doctors are more inclined to suspect cancer in older patients and younger patients are more likely than older people to have consulted with a doctor 3 or more time before referral. Even when referred, younger patients may be referred through a less urgent route compared to older ones. A delay in diagnosis may result in cancer progressing to a less curable stage. Some studies suggest that for some cancers, younger patients have more advanced disease at diagnosis compared to older ones.
Many clinical guidelines for cancer recognition and referral use age as a key criterion to determine which patients require urgent investigation for suspected cancer. However, several recent reports have suggested that colorectal cancer is becoming more common in younger patients. Although similar changes have been described in other types of cancer, the data are more limited and there is a lack of comprehensive reviews of the evidence. It prompted the study team to perform a rapid review of incidence trends for 12 cancers in younger adults.
The study team searched MEDLINE, Embase and Web of Science for studies describing age-related incidence trends for colorectal, bladder, lung, oesophageal, pancreatic, stomach, breast, ovarian, uterine, kidney and laryngeal cancers and multiple myeloma. Younger patients with cancer were defined as individuals diagnosed below the age threshold in the NICE guideline for the specific cancer referral. Paediatric patients, defined as those younger than 18-year, were excluded.
The searches were limited to studies published from 1995 onwards. In total, 98 studies met the inclusion criteria. All studies had a retrospective design and were based on national or local cancer registries. A total 68 studies originated from North America, 24 from Europe, 3 from Oceania, 2 from Asia and 1 from South America, 5 studies compared several countries worldwide. Most studies contributed data for 1 type of cancer, but 8 provided data for 2 or more.
The authors identified 3 distinct groups of cancers: 1. those with consistent evidence of rising incidence in younger age groups, in particular colorectal, breast, pancreatic, kidney and uterine cancers, 2. those with consistent evidence of decreasing incidence in younger age groups, in particular bladder, lung and laryngeal cancers, and 3. those for which the data were deemed inconclusive, in particular stomach, oesophageal, ovarian cancers and multiple myeloma.
For the cancers with a clear trend towards an increase or a decrease, the authors considered the evidence strong when coming from more than 10 good-quality studies and moderate when coming from 10 or less good-quality studies.
The authors commented that this is the first review examining epidemiological evidence across a range of 12 cancer types with age-related referral criteria, to determine whether their incidence is increasing in younger patients.
Changes in the prevalence of lifestyle associated risk factors in high-income countries may be contributing to the trends. Obesity, which has become more prevalent in high-income countries in the last few decades, is a risk factor for 4 out of 5 cancer types with rising incidence (colorectal, pancreatic, kidney, and uterine cancers), whilst its role in early onset breast cancer is more controversial. Variations in patterns of childbearing and breastfeeding or increased use of oral contraception may be contributing to the rise in breast and uterine cancers incidence in younger generations. In addition, 3 cancer types linked to smoking (lung, laryngeal and bladder) show a clear reduction of incidence, what is in line with the decrease in smoking rates in younger adults in recent decades. Another smoking-linked cancer, oesophageal squamous cell carcinoma, also had some evidence of decrease in younger age groups.
Furthermore, changes in clinical practice, such as increased diagnostic activity, introduction of cancer screening programmes, change in management of other conditions, or change in disease classification, may have also contributed to the observed changes incidence.
The authors stated that policymakers need to be aware of the incidence trends when reviewing guidelines and screening programmes. Addressing preventable risk factors such as excess weight may help curb the increase of these malignancies in younger generations.
di Martino E, Smith L, Bradley SH, et al. Incidence trends for twelve cancers in younger adults—a rapid review. Br J Cancer 2022;126:1374–1386. DOI: https://doi.org/10.1038/s41416-022-01704-x