Age effect: The present study revealed that the incidence rate of female breast cancer was the highest among the age group of 45–70 years, consistent with global observations (5). In this investigation, the peak age effect for female breast cancer incidence occurred in the 45–49-year-old group. Luan et al. (6) assessed the age-period-cohort effects on female breast cancer incidence in Hong Kong, Shanghai, and White and Black populations in Los Angeles. Although the age effect also peaked in the 45–49-year-old group in Shanghai, distinct patterns were observed in the other three populations. These diverse age effect patterns across various populations might be attributable to the potential differences in the prevalence of tumor-related genes (7).
Ding et al. (8) discovered a rapid increase in breast cancer mortality rates from the 20–24 age group to the 45–49 age group, followed by a slower rate of increase. Wang et al. (9) noted that the age effects of breast cancer mortality plateaued in the 55–59 age group and then gradually declined in Japan and Korea, while the age effect consistently increased with age in Singapore. In the present study, a small peak in the female breast cancer mortality rates was observed within the 50–54 age group. Further investigation is necessary to determine the reasons for the elevated risk in this particular age group.
Period effect: Our study identified increasing period effects in female breast cancer incidence and mortality rates from 2003 to 2017, aligning with findings from previous research (8-10). This observation suggests that socioeconomic transformations and modernized lifestyle changes may constitute the primary factors contributing to the rise in breast cancer incidence and mortality in China.
Screening strategies are crucial influencing factors for incidence and mortality trends in breast cancer. Krishnamoorthy et al. (11) conducted an analysis of worldwide breast cancer incidence rate trends across various regions. Their findings indicated that the Americas had the highest breast cancer incidence, but it was the one region in which the incidence rate had been declining. Likewise, the period effect in the Americas displayed a decreasing trend. These findings suggest that the breast cancer screening programs in the Americas have reached a saturation point, and their health benefits have become evident. However, due to the limited coverage of screening programs in China, the period effect has not yet been reversed. Drawing on the experiences of the Americas, it can be predicted that the period effect and the ASIR for breast cancer will continue to rise for an extended period in China.
Cohort effect: Our research identified a decreasing cohort effect in incidence and mortality rates for female breast cancer, consistent with findings from previous studies (6,8–10). This decline in cohort effect suggests that older birth cohorts face a higher risk of developing female breast cancer than younger cohorts. The possible reasons for this reduction may include healthier living habits and enhanced health awareness among younger generations, along with improvements in public health policies and clinical diagnosis and treatment options in recent years.
It is important to note, however, a slight upsurge in cohort effect was observed among younger populations in rural areas of China. This reversal may result from an increased exposure to emerging risk factors, such as sedentary lifestyles (12), changes in reproductive behaviors (e.g., delayed first childbirth, nulliparity, and oral contraceptive pill use), and diminished breastfeeding practices (13). These factors come in addition to well-established risks such as physical inactivity, excessive body weight, and diabetes (14).
The early diagnosis rate for female breast cancer in China was significantly higher than that observed for other types of cancer (15). Our data further revealed that between 2003 and 2017, the mortality rate for female breast cancer increased at a slower pace than the incidence rate. This evidence suggests that current screening programs have yielded substantial benefits through early detection and treatment. However, it is critical to recognize that effective primary prevention strategies for addressing new risk factors remain limited. Without them, reducing breast cancer incidence in the short term may be unattainable. As such, there is a pressing need to develop comprehensive public health intervention strategies, particularly for younger generations and vulnerable populations.
In the current study, we utilized continuous surveillance data from 22 cancer registries spanning 2003 to 2017, offering a more accurate depiction of trends in rates as compared to alternative multi-sectional datasets. Additionally, the use of ICD-10 coding for cancer registry data enhances the precision of our analysis. Nonetheless, some limitations exist within this dataset, primarily due to its restricted population coverage, particularly in rural areas. This results in increased fluctuation within trends and broader 95% CI for risk ratio point estimation. Furthermore, the observation period in this study is relatively shorter than those found in research conducted in other countries.
In conclusion, the present study examined the period from 2003 to 2017 and found increasing incidence rates of breast cancer across all age groups and geographic locations. However, rising mortality rates were observed predominantly among women over 50 years old, particularly in rural areas. These trends can be primarily attributed to period effects, while cohort effects generally decreased. Notably, a slight upward trend was detected for younger generations in rural regions. Consequently, it is crucial to adjust and refocus current intervention strategies for female breast cancer in China to adequately address the growing burden of this disease.