Attributable breast cancer burden in Malaysia: mammographic density, lifestyle, and hereditary factors

Breast cancer is the most common cancer affecting women worldwide, and in many parts of Asia, the number of new cases is rising quickly. While scientists have long known that some risks for this disease are fixed, such as a person's genes or family history, others can be changed through daily choices. These changeable factors include a person's weight, whether they are exposed to secondhand smoke, and how they live their life. To stop the disease before it starts, health officials need to know which of these factors are the biggest drivers in their specific communities. A one-size-fits-all approach often fails because the mix of risks changes depending on where people live, their ethnic background, and their age. Understanding exactly how much each factor contributes to the total number of cases allows doctors and policymakers to focus their efforts where they will save the most lives.

In Malaysia, a team of researchers set out to map these risks specifically for the country's diverse population, which includes Malay, Chinese, and Indian women. They did not conduct new experiments but instead combined existing data from large national health surveys with scientific estimates of how strongly each risk factor causes cancer. By using a method that simulates how these factors work together, they calculated the "attributable burden," which is a way of saying what percentage of breast cancer cases in the country could theoretically be prevented if a specific risk factor were removed. Their work reveals that the most significant driver of breast cancer in Malaysia is not a single lifestyle habit, but a physical characteristic of the breast tissue itself that many women are unaware of.

The study found that the density of breast tissue, which refers to how much fibrous and glandular tissue a woman has compared to fatty tissue, accounts for the largest share of the disease burden. In the Malaysian population, this factor is responsible for roughly one-third of all breast cancer cases. This is a substantial proportion, meaning that if breast density could be lowered across the entire population, a significant number of cases could be avoided. Following this, the researchers identified body weight as the next most critical factor. Being overweight or obese contributes to about fifteen percent of cases, while exposure to secondhand smoke accounts for another eight percent. These three factors combined represent the majority of the preventable risk in the country.

The researchers also discovered that the importance of these risks shifts as women age. Before menopause, reproductive choices play a more prominent role. Factors such as having no children, delaying childbirth until after age thirty, or never breastfeeding are more influential in this younger group. However, once women pass menopause, the landscape changes. Metabolic factors, particularly carrying extra weight, become the dominant drivers of risk. This distinction suggests that prevention strategies need to evolve as a woman moves through different stages of life, focusing on reproductive health for younger women and weight management for older women.

Ethnicity also plays a clear role in which risks matter most. The study showed that breast density is the strongest contributor for Chinese women, whereas excess body weight is the primary driver for Malay and Indian women. This finding highlights that a public health message that works for one group may not be the most effective for another. Furthermore, the researchers looked at women born in different eras and found that those born after 1945 face a higher burden from both breast density and obesity compared to older generations. This shift likely reflects changes in lifestyle and diet over time, suggesting that the risk profile for breast cancer is becoming more influenced by modern living conditions.

While the study confirmed that family history and specific genetic mutations are important, their overall contribution to the total number of cases in Malaysia is smaller than that of the modifiable factors. Family history and genetics together account for about twelve percent of cases. Other factors, such as alcohol consumption, lack of physical activity, and the use of certain hormones, were found to have a much smaller impact on the overall burden, each contributing less than four percent. The researchers noted that while some factors like breast density are difficult to change through lifestyle alone, the strong link to weight and secondhand smoke offers clear opportunities for prevention.

The authors emphasize that their findings are based on simulations using the best available data, which means the results are estimates rather than direct measurements of every individual case. They also acknowledged that because they used the same risk estimates for all ethnic groups, the specific numbers for each group might vary slightly, but the overall pattern remains clear. The study concludes that a substantial portion of breast cancer in Malaysia is linked to factors that can be changed. By tailoring screening and prevention strategies to account for age, ethnicity, and the specific mix of risks in different communities, health officials can better target their efforts to reduce the disease burden in the years to come.