Breast Cancer Incidence Is Rising Among Young Women

In Western populations, the most frequently diagnosed cancer among women aged 20 to 49 is breast cancer , which is also the leading cause of cancer-related death in this age group.

Compared with older women, younger women are more likely to develop breast cancers with aggressive biological features. These include larger tumors, more advanced tumor stages, negative hormone receptor status (estrogen receptor [ER] and progesterone receptor [PR]) and HER2 overexpression. All these factors contribute to poorer outcomes in young patients. In addition, breast cancer screening programs are not available for women under 40, apart from those at high risk.

Recent studies have found rising breast cancer incidence among young women, but few have comprehensively described trends by hormone receptors, stage and race.

The Latest Research

Research published on January 26, 2024, in JAMA Network Open found that breast cancer incidence among US women aged 20 to 49 increased from 2000 to 2019, particularly after 2016.

Breast cancer incidence among US women aged 20 to 49 varies by race and hormone receptor status.

The researchers found that changes in incidence differed by race and hormone receptor status, highlighting "the need for further research into specific breast cancer risk factors among young women and potential targeted prevention strategies for at-risk groups" as a priority.

The study included 218 thousand women with breast cancer from Surveillance, Epidemiology, and End Results (SEER) registries. Patients were aged 20 to 49. Most (58.3%) were non-Hispanic White; 17% were Hispanic, 12.4% non-Hispanic Black, 11.6% Asian or Pacific Islander and 0.7% American Indian or Alaska Native. Most patients (61.5%) had estrogen receptor (ER)-positive/progesterone receptor (PR)-positive disease.

From 2000 to 2019, breast cancer incidence in this age group increased by 0.79% annually. According to the researchers, incidence increased "gradually" between 2000 and 2016 (annual percentage change [APC], 0.24%) and "dramatically" after 2016 (APC, 3.76%).

The highest age-standardized incidence rates were seen among non-Hispanic Black patients (70.7 per 100,000 people) and non-Hispanic White patients (69.7 per 100,000). Incidence was lowest among non-Hispanic American Indian or Alaska Native patients (52.6 per 100,000 people) and Hispanic patients (52.8 per 100,000).

In the youngest age groups, incidence was highest among non-Hispanic Black patients, with incidence rate ratios of 1.53 at ages 20 to 29 and 1.15 at ages 30 to 39.

During the study period, age-standardized incidence rates for estrogen receptor (ER)-positive and progesterone receptor (PR)-positive breast cancers increased by an annual average of 2.72%. Likewise, ER-positive but PR-negative cases showed an annual average increase of 1.43% in age-standardized incidence. However, ER-negative and PR-positive cases showed an annual average decline of -3.25% in age-standardized incidence over the study period. These findings indicate different trends over time in breast cancers with particular hormone receptor profiles.

Summary of the Main Findings

• Breast cancer cases have increased among young women in the United States over the past 20 years. This increase has occurred across different racial and age groups.
• ER+ tumors are more common at stages 1 and 4 and less common at stages 2 and 3. ER- tumors are less common at stages 1 and 4 and more common at stages 2 and 3.
• Non-Black Hispanic women aged 20-29 and 30-39 experienced the largest increases in breast cancer incidence. The increase was particularly evident in ER+ tumors, while ER- tumors declined.

Conclusion

These results provide important information for preventing breast cancer among young women. Understanding the reasons behind the different incidence trends by age, race and estrogen receptor (ER) positivity may help develop tailored prevention strategies. This can enable researchers and health policymakers to create more effective prevention and early detection programs for at-risk groups. A better understanding of how race and hormone receptor status affect breast cancer risk may therefore strengthen prevention efforts for young women.

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What Might Be Driving the Rise in Breast Cancer Among Young Women?

The study findings and existing literature offer several hypotheses about potential causes of this increase:

1. Hormone Receptor Status

• An Increase in Estrogen Receptor-Positive (ER+) Tumors: The study observed rising incidence rates of ER+ tumors. These tumors have been associated with factors such as hormone levels and the duration of hormone exposure.

2. Demographic and Socioeconomic Factors

• Race and Ethnicity: The study identified high incidence rates among young non-Black Hispanic women. This may be associated with genetic susceptibility, lifestyle, socioeconomic factors and access to healthcare.
• Cohort and Period Effects: Age-period-cohort analysis showed that rising breast cancer incidence was associated with particular birth cohorts and time periods. This may reflect lifestyle changes and environmental exposures across generations.

3. Lifestyle and Environmental Factors

• Reproductive Factors: Reproductive patterns such as a later first birth, having fewer children and breastfeeding briefly or not at all may increase the risk of ER+ breast cancer.
• Obesity and Physical Activity: Increasing obesity and insufficient physical activity may raise breast cancer risk, particularly among young women.
• Alcohol Consumption and Smoking: Increased alcohol consumption and smoking may raise the risk of breast cancer.

For this age group, obesity and alcohol may be the two most important reasons for the increased risk of breast cancer.

4. Genetic and Familial Risk Factors

• Genetic Mutations Such as BRCA1 and BRCA2: High-risk genetic mutations may increase the risk of breast cancer at a young age.
• A Family History of Breast Cancer: Women with a family history of breast cancer have a higher risk of developing it at a young age.

5. Screening and Diagnosis

• Improvements in Early Diagnosis and Screening Techniques: Advanced screening techniques can allow breast cancer to be diagnosed earlier, which may help explain rising incidence rates among young women.

This increase in breast cancer incidence is complex and multifactorial. Comprehensive research and public health measures are therefore needed to better understand risk factors and prevention strategies. Developing targeted prevention and early detection strategies to reduce breast cancer risk among young women is particularly important.