Breast cancer has overtaken lung cancer to become the most diagnosed cancer globally and is increasing in countries where rates of breast cancer have been historically low.

The report Global Cancer Statistics 2020 was a collaboration from the American Cancer Society (ACS) and the International Agency for Research on Cancer (IARC). It found that an estimated 19.3 million new cancer cases and almost 10 million cancer deaths occurred in 2020.

Female breast cancer was the most commonly diagnosed cancer, with an estimated 2.3 million new cases (11.7%), followed by lung (11.4%), colorectal (10.0%), prostate (7.3%), and stomach (5.6%) cancers.

The authors said that the dramatic changes in lifestyle and built environment have had an impact on the prevalence of breast cancer risk factors such as excess body weight, physical inactivity, alcohol consumption, postponement of childbearing, fewer childbirths, and less breastfeeding.

Death rates of breast cancer among women in transitioning countries were even higher compared with the rates among women in transitioned countries (15 and 12.8 per 100,000, respectively), despite the substantially lower incidence rates (29.7 and 55.9 per 100,000, respectively).

Guidelines needed to promote early detection of breast cancer

Hyuna Sung, PhD, lead author of the report and Principal Scientist at the ACS, said: "As the poor outcome in these countries is largely attributable to a late-stage presentation, efforts to promote early detection, followed by timely and appropriate treatment, are urgently needed through the implementation of evidence-based and resource-stratified guidelines."

Data show that lung cancer remained the leading cause of cancer death with an estimated 1.8 million deaths (18%), followed by colorectal (9.4%), liver (8.3%), stomach (7.7%), and female breast (6.9%) cancers. Lung cancer death rates are 3 to 4 times higher in transitioned countries than in transitioning countries, however, this pattern may well change as the tobacco epidemic evolves given that 80% of smokers reside in low- and middle- income countries. With about two-thirds of lung cancer deaths worldwide attributable to smoking, the disease can be largely prevented through effective tobacco control policies and regulations.

Data in this report do not reflect the impact of the Covid-19 pandemic as they are based on cancer data collected in earlier years, and the full extent of the impact in different world regions is currently unknown. According to the report, delays in diagnosis and treatment, including suspension of screening programs and reduced availability of and access to care, are anticipated to cause a short-term decline in cancer incidence followed by increases in advanced-stage diagnoses and cancer mortality in some settings.

Freddie Bray, senior author of the report and Head of the Section of Cancer Surveillance at IARC, added: "The burden of cancer incidence and mortality is rapidly growing worldwide, and reflects both aging and growth of the population, as well as changes in the prevalence and distribution of the main risk factors for cancer, several of which are associated with socioeconomic development.

"Effective and resource-sensitive preventative and curative interventions are pertinent for cancer diagnosis. Tailored integration into health planning can serve to reduce the global burden of cancer and narrow the evident cancer inequities between transitioning and transitioned countries observed today."