Breast cancer has hit the spotlight. While a global study finds it has now overtaken lung cancer as the world’s most diagnosed malignancy, a US group reports that its decline in younger women has stopped and another makes a contentious call for earlier screening.
The first study, published in CA: A Cancer Journal for Clinicians, found an estimated 2.3 million new cases of female breast cancer were diagnosed in 2020. This represents 11.7% of all new cancers, which topped 19.3 million.
It found that incidence is increasing rapidly in countries where rates were previously low, such as South America, Africa and Asia. Lead author Hyuna Sung, from the American Cancer Society, and colleagues attribute this to social and economic transitions.
“Dramatic changes in lifestyle, sociocultural and built environments brought about by growing economies and an increase in the proportion of women in the industrial workforce have had an impact on the prevalence of breast cancer risk factors,” they write.
These changes include earlier menarche, later childbearing and menopause onset, less breastfeeding, oral contraceptives, hormone therapy and lifestyle factors such as excess body weight and physical inactivity, which they say have “resulted in a convergence toward the risk factor profile of western countries and narrowing international gaps in breast cancer morbidity”.
Lung, colorectal, prostate and stomach cancers were the next most diagnosed after breast cancer. However, lung cancer accounted for the most deaths, followed by colorectal, liver, stomach and then female breast cancers (which accounted for 6.9% of deaths).
While breast cancer cases remain highest in westernised countries, with Australia, Europe and the US topping the list, death rates are 17% higher in women from less developed regions which could be attributed to poor health infrastructure and late detection.
Establishing prevention programs is challenging, but the authors say, “efforts to decrease excess body weight and alcohol consumption and to encourage physical activity and breastfeeding may have an impact in stemming the incidence of breast cancer worldwide.”
In the US, breast cancer death rates have stopped falling in women under 40, according to a study published in the journal Radiology, based on data from the National Centre for Health Statistics and the Surveillance, Epidemiology and End Results program.
This cohort accounts for only 4% to 5% of cases. But, while deaths continued to drop in women aged 40 to 79 years between 2010 and 2017, the study found that in under-40s they increased by 0.5% (2.8% in 20-29-year-olds and 0.3% in those aged 30-39), ending a steady decline since 1989.
The rise is negligible but concerning, according to lead author R Edward Hendrick from the University of Colorado. “It’s clear that mortality rates in women under 40 are no longer decreasing,” he says. “I estimate that in two to three years, the mortality rate will be increasing significantly in these women.”
The authors attribute this, in part, to increased incidence of metastatic, or secondary, breast cancer, which grew by more than 4% per year since 2000 and paralleled mortality rates since 2010 in that age group.
Mammography screening is another possible factor, they add, suggesting early detection could be contributing to the continued decline in death rates of at-risk women over age 40. In all, Henrick says the trend needs further investigation.
“Our hope is that these findings focus more attention and research on breast cancer in younger women and what is behind this rapid increase in late-stage cancers.”
Associate Professor Carolyn Nickson, who is a spokesperson for the Cancer Council and a researcher in breast cancer screening and diagnosis at Melbourne University, notes that the demographic breakdown in women in the study is important to note.
“We may observe similar trends in Australia overall,” says Nickson, “however it is important to consider outcomes for different groups of women – in Australia this means understand outcomes for women according to their ethnicity, socio-economic status, remoteness, and Indigenous status.”
She adds that large-scale studies in the US can’t be easily applied to Australia. “The US does not deliver a national screening program free…as we do in Australia through BreastScreen.”
Another US group suggests that breast density screening of 40-year-old women should guide future mammogram procedures, in a study published in the Annals of Internal Medicine.
High breast density increases the risk of breast cancer, but most women don’t know their breast density until their first mammogram at age 50, when screening is first recommended in the US.
The researchers, led by Ya-Chen Tina Shih from the University of Texas, modelled health outcomes and cost-effectiveness of seven different breast cancer screening strategies.
Results suggest that a baseline breast density assessment for every woman at age 40, followed by annual screening for those with dense breasts and biennial screening after 50 years of age in women without dense breasts, would produce the lowest mortality and highest cost savings.
However, it was also associated with more lifetime mammograms and more false positives and overdiagnosis.
An accompanying editorial notes that risk-based screening improves breast cancer outcomes but that age and other risk factors such as family history should be factored in. It also highlights the limitations of using breast density.
“The fundamental problem with measuring breast density and assigning screening frequency on the basis of one reading is that not everyone with dense breasts is at increased risk for breast cancer,” write Karla Kerlikowske and Kirsten Bibbins-Domingo from the University of California.
They also highlight several flaws in the model’s assumptions and inconsistencies with other research, arguing that “until a more robust risk-based strategy is identified, the [data] … support screening biennially from ages 50–74 years.”
Nickson agrees that breast density should be considered alongside other factors, as her research in Australia is currently doing.
“Our government funded project in Australia is investigating more personalised, risk-based screening protocols that consider women’s breast density but also their family risk of breast cancer and other risk factors that could be routinely and reliably measured in women,” she says.
“This US study is useful, but it is important to note we have a very different health system in Australia. While the cost-effectiveness analysis may be relevant to the US setting, different estimates are required for Australia.”