While cancer remains rare among young adults, with an incidence rate much lower than among those over 60, the study shows that the incidence of all cancers increased by 1.62% per year between 2000 and 2014, then decreased by 0.79% per year between 2015 and 2020.

The incidence of six cancers is on the rise: Hodgkin’s lymphoma, glioblastoma, liposarcoma, colorectal cancer, breast cancer, and kidney cancer. These findings call for further studies to better identify the underlying risk factors responsible for these trends in order to promote or strengthen prevention among young adults.

A methodology that takes into account the latest international consensus

This study presents the distribution of cancers by age group, the incidence of all cancers combined over the 2000–2020 period, and its trends by cancer groups and subgroups, in the study population and in the departments of mainland France covered by a general cancer registry.

It was conducted using data covering 19 departments (representing 24% of the population of mainland France) to describe the distribution of cancers and estimate their incidence over the entire period. Changes in incidence between 2000 and 2020 were estimated using data covering 11 departments^¹ (18% of the population).

With the aim of aligning French surveillance data with the latest international consensus, this study is the first to consider the broader population of 15–39-year-olds (the previous study focused on 15–24-year-olds) and categorizes cancers according to the new Barr classification² published in 2020.

This new classification categorizes cancers based on the type of cell affected (morphological criterion), followed by the organ they affect (topographical criterion).

Cancer Rates Vary by Age Group and Gender

Between 2000 and 2020, 54,735 young adults (AJA) diagnosed with cancer were recorded across the 19 departments studied. These results do not cover the entire population but are comprehensive for the area in question.
Leukemias, lymphomas, central nervous system tumors, and sarcomas are the most common among 15- to 19-year-olds (66%) and account for only 19% of cancers among 35- to 39-year-olds. Conversely, melanomas and certain carcinomas increase from 23% to 73% between these two age groups. In men, the most common cancers are malignant testicular germ cell tumors, Hodgkin lymphomas, non-Hodgkin lymphomas, melanomas, gastrointestinal carcinomas, and urinary tract carcinomas. In women, breast cancer, thyroid cancer, and melanomas are the most common.

The age-standardized incidence rate (ASIR) for all cancers among 15- to 39-year-olds from 2000 to 2020 is 58.1 per 100,000 person-years, lower among men than among women. Standardization allows for comparing incidence rates between countries with different age structures; this SIR is comparable to those observed in the United States or Europe.

Contrasting trends in incidence by cancer type between 2000 and 2020

The incidence of certain cancers is decreasing, such as that of melanomas (-3.05% per year), likely due to preventive measures, and that of head and neck cancers (-1.24%), a heterogeneous group that limits the interpretation of the results.

The incidence of certain cancers remained stable toward the end of the period: malignant testicular germ cell tumors, following an increase through 2012, and carcinomas of the genital tract, which declined through 2013 and consist primarily of cervical cancers. As in other countries, the incidence of this cancer could decrease if HPV vaccination coverage increases. It is important to continue efforts aimed at achieving 80% vaccination coverage among adolescents by 2030.

Certain trends in incidence can be attributed to variations in diagnostic practices and/or changes in the classification systems used by registries: the increase in the incidence of essential thrombocythemia and astrocytic tumors, the decrease in that of oligodendrogliomas, and the rise followed by a decline in that of thyroid cancers.

An average annual increase in the incidence of six cancers was observed over the entire period: Hodgkin’s lymphomas (+1.86%), glioblastomas (+6.11%), liposarcomas (+3.68%), colorectal carcinomas (+1.43%), breast carcinomas (+1.60%), and renal carcinomas (+4.51%).
An increase in Hodgkin’s lymphomas is also observed in other European countries, primarily for the sclerodermic-nodular form; the specific causes of Hodgkin’s lymphoma remain to be identified.

Results concerning central nervous system tumors should be interpreted with caution: changes in the classification of these tumors occurred during this period, and improvements in histopathological diagnosis and molecular biology, in conjunction with advances in imaging, have an impact on the analysis by histological type. An increase in the incidence of histologically confirmed glioblastomas has already been reported in France^³.

Although liposarcoma is rare, an increase in incidence is observed. The introduction of molecular genetics into its diagnosis may have had an impact, but is not sufficient to explain the rise in this cancer, for which risk factors have not been identified.

An increase in the incidence of breast cancer, tumors of the digestive system (61% of colorectal cancers), and tumors of the urinary system (87% of kidney cancers) is also observed internationally. Obesity could be a factor explaining the increase in cancers of the digestive system (including colorectal) as well as kidney cancers, though this remains to be demonstrated.

These new findings help refine our understanding and guide research, care, and prevention efforts. However, further studies are needed to confirm these findings, which were generated at the subnational level, and to better understand the risk factors and exposures driving the observed increases.