Trends and Age-Period-Cohort Effects in Breast Cancer Incidence and Mortality Among Women Aged 20 Years and Older from 2009 to 2023 in Quzhou, China

Breast cancer is the most common cancer affecting women worldwide and remains a leading cause of cancer-related death. While the disease is influenced by biology and age, its patterns are also shaped by the era in which a woman lives and the generation she belongs to. Scientists often look at three distinct time-related factors to understand these patterns. First is age, which reflects the natural changes in the body as a person grows older. Second is the time period, representing the specific years when events like new medical technologies or public health policies affect everyone living at that time. Third is the birth cohort, which tracks groups of people born in the same years who share similar life experiences, such as dietary habits or exposure to environmental changes. Understanding how these three forces interact helps public health officials see not just how many people are getting sick, but why the numbers are changing and where the greatest risks lie.

In the city of Quzhou, located in eastern China, researchers set out to examine these trends over a fifteen-year span, from 2009 to 2023. During this time, the local government implemented a major screening program known as the "two cancers" initiative, designed to find breast and cervical cancer early in women. The goal was to see if this effort, which began in rural areas and later expanded to include urban residents, had successfully lowered the number of new cases or deaths. The team gathered data from a provincial health system that tracks chronic diseases, looking at every woman aged twenty and older who was diagnosed with breast cancer or died from it. They analyzed the numbers to see if the disease was becoming more common, if it was killing more people, and how these patterns shifted between city and country, across different age groups, and for women born in different decades.

The results revealed a clear and steady rise in both new cases and deaths across the region. The number of new diagnoses per 100,000 women more than doubled, jumping from 21 in 2009 to 58 in 2023. While the number of deaths also increased, rising from 6 to 8 per 100,000, the growth in new cases was much sharper. This surge in diagnoses is partly attributed to the screening program itself. By actively looking for the disease, doctors found many cases that might have otherwise gone unnoticed until they became advanced. The data showed that the rate of new diagnoses grew very quickly at first, then slowed down, suggesting that the screening efforts may have reached a point where most detectable cases were already being found.

A closer look at where these women lived painted a more complex picture. In urban areas, the number of new cases rose sharply at the beginning of the study but then began to fall after 2014. In contrast, rural areas saw a continuous climb in diagnoses throughout the entire fifteen years. This difference likely stems from the timing and reach of medical resources. Cities had access to healthcare and health education earlier, leading to an initial spike in detection followed by a stabilization. Rural areas, which received the screening program later, experienced a sustained increase as awareness and access improved. Despite these differences, the gap between city and country rates narrowed over time, indicating that rural screening efforts were successfully catching up. Interestingly, while the number of new cases dropped in cities, the death rate there remained relatively steady. In rural areas, however, the death rate continued to climb, suggesting that while more women were being diagnosed, the ability to prevent death in those areas still lagged behind.

The researchers also examined how age influenced the risk of getting and dying from the disease. They found that the risk of developing breast cancer rises as women get older, peaking for those between the ages of 45 and 54. After this peak, the risk of a new diagnosis begins to decline slowly. However, the risk of dying from the disease tells a different story: it keeps climbing steadily as women age, with the highest risk found in those over 85. This suggests that while older women are less likely to develop a new tumor than those in their late forties, if they do get the disease, it is harder to survive, likely due to other health issues and a reduced ability to tolerate treatment. The average age at which women were diagnosed also shifted upward, moving from about 50 years old in 2009 to nearly 56 by 2023. This shift reflects broader changes in the population, including better nutrition and a general aging of the community.

Finally, the study looked at the generations of women born in different years to see if the risk of breast cancer changed over time. For women born between 1924 and 1993, the risk of developing the disease actually decreased with each new generation. This decline is likely due to better health education and lifestyle changes that occurred over the decades. However, a sharp reversal happened for women born after 1993. For this younger group, the risk began to rise again. The researchers suspect this increase is linked to modern lifestyle factors, such as changes in diet, higher rates of obesity, and shifts in reproductive habits, including having children later in life or having fewer children. While the risk of getting the disease has gone up for these younger generations, the risk of dying from it has generally declined for birth cohorts from 1924 to 2003, a sign that medical treatments are becoming more effective at saving lives even as the disease becomes more common.

The study concludes that while the screening programs in Quzhou have been successful in finding more cases early, the overall burden of breast cancer is still growing. The rise in diagnoses among younger women and the continued increase in rural death rates highlight that the fight against the disease is not yet won. The findings suggest that public health efforts must continue to evolve, focusing not just on finding cancer early but also on ensuring that treatment is accessible and effective for everyone, regardless of where they live or how old they are. The data serves as a reminder that while medical progress is real, the changing patterns of the disease require constant attention and adaptation to protect women's health.