Breast density is a measure of fibro-glandular to fatty tissue in the breast. Research has indicated that about 50% of women in their 40s have dense breasts [1], which, reportedly, increases the risk for breast cancer. Specifically, women with a dense area comprising 75% or more of the breast face a 4.6 times greater risk of breast cancer than women with a dense area smaller than 5% [2]. A highly dense breast may also lower the sensitivity of screening test to detect breast cancer, falling from 80% to 98% in less dense breasts to 30% to 64.4% in highly dense breasts [3]. Consequently, interval cancer rates are higher among women aged 50 to 74 years with extremely dense breasts or women aged 70 to 74 years with heterogeneously dense breasts [4]. Although the impact of higher breast density on breast cancer risk and mammographic masking is well known, previous studies have reported that the majority of women do not know their own breast density status and are not familiar with breast density [4-6].

With evidence of breast density as both an individual risk factor for breast cancer and a masking factor of mammographic examination, the United States mandates nationwide that women are to be informed of their breast density status [4,7,8]. This was initially implemented in an attempt to increase female awareness of the importance of breast density in breast cancer; however, others argued that it could elicit unnecessary psychological responses among women [9-11]. Research has shown that European American women who are aware of their breast density status have a stronger perception of breast cancer risk and worry, compared to those who were unaware. Yeh et al. [11] also documented increased perceived risk and worry about breast cancer among women after hearing about their breast density status from mammography tests. Psychological reactions, however, are not necessarily negative in that higher perceived risk and cancer worry might facilitate better screening behavior and drive intentions to undergo screening [12-16]. Indeed, some studies have reported that psychological reactions affected by awareness of breast density facilitated positive health behaviors [12,17,18]. Generally, a U-shaped relationship between psychological effect and favorable screening behaviors has been recognized [16].

In South Korea, the National Cancer Screening Program for breast cancer was launched for women aged 40 years and older in 2002 [19]. Since 2007, women who have undergone breast cancer screening can learn their own breast density through the Breast Imaging-Reporting and Data System (BI-RADS) classification (4th edition) [20]. Meanwhile, however, studies have yet to examine the effects of becoming aware of one’s breast density on psychological reactions, such as perceived risks and worry about breast cancer, among Korean women. Therefore, this study was conducted to assess degrees of perceived risk and cancer worry for breast cancer according to knowledge and awareness of one’s own breast density status among Korean women. Finally, we investigated how awareness and knowledge of breast density could be related to intentions to undergo mammography screening.

The sociodemographic characteristics of the study population are summarized according to awareness of breast density status in Table 1. Among the respondents, 62.0% answered that they did not know their breast density status. Women in their 60s, living in a rural area, with lower income and education level, without private health insurance, and no history of breast cancer screening within the past 2 years demonstrated less awareness of breast density. Women who were college graduates (adjusted odds ratio [aOR], 2.05; 95% confidence interval [CI], 1.33 to 3.16) or underwent breast cancer screening within the past 2 years (aOR, 1.63; 95% CI, 1.30 to 2.03) were more likely to be aware of their breast density status.

Breast density knowledge among Korean women is summarized in Table 2. Only 38.2% of women correctly answered that high breast density lowers mammographic sensitivity, and 64.4% of them correctly answered that high breast density increases breast cancer risk. The proportion of women who correctly answered both questions, who were categorized as having a good level of breast density knowledge, was 29.7% (Table 2). Of note, the proportion of women correctly responding to the breast density-related knowledge questions was significantly higher among those who knew that they had dense breasts. Concerning the information resources where women collected breast density knowledge, half of the women received information from hospitals or clinics.

Scores for perceived absolute risk, perceived comparative risk, and cancer worry about breast cancer are summarized in Table 3. Women aged 50-59 years, having higher socioeconomic status, who completed college education or higher, who had a family history of cancer, had breast density awareness, and a good level of breast density knowledge showed a significantly higher level of perceived risk and worry (Table 3).

In the ordinal regression analysis, women who were aware of their dense breast status were more likely to have higher perceived absolute risk, perceived comparative risk, and cancer worry (Table 4). Notably, women who were aware of their high dense breast had perceived risk and cancer worry scores three times higher than their counterparts. Further, women with a good level of knowledge on breast density reported a significantly higher level of perceived absolute risk (aOR, 1.82; 95% CI, 1.46 to 2.28), perceived comparative risk (aOR, 1.50; 95% CI, 1.19 to 1.89), and cancer worry (aOR, 1.75; 95% CI, 1.41 to 2.19). In general, women with moderate and high monthly household income (≥ $3,000) and with a family history of cancer showed a higher level of perceived risk and cancer worry. Interestingly, women who had private cancer insurance showed a lower level of perceived comparative risk and cancer worry. In contrast, women who had graduated high school or more were more likely to have higher perceived absolute risk.

Among respondents, 61.8% of women reported that they had intentions to undergo breast cancer screening (Table 5). The proportion thereof was significantly higher among women with the highest level of household income, private cancer insurance, a family history of cancer, and a college education. Moreover, women with a high/very high level of perceived absolute risk and perceived comparative risk and with an often/always level of cancer worry were more likely to express intentions to undergo breast cancer screening, as were women with a dense breast and a good level of knowledge on breast cancer. The results from the three multiple logistic regression models are provided in Table 5. In model 1, women who had a high or very high level of perceived comparative risk (aOR, 1.82; 95% CI, 1.09 to 3.03) and who often or always worried about developing cancer (aOR, 1.85; 95% CI, 1.14 to 3.01) were more likely to undergo breast cancer screening in the next 2 years. Perceived absolute risk showed no significant association with breast cancer screening intentions. In model 2, women who knew their breast density status were more likely to have screening intentions, especially those with dense breasts who 4.66 times more frequently reported having screening intentions (aOR, 4.66; 95% CI, 3.28 to 6.63 for dense breast women). Also, women who had a good level of knowledge of breast density were more likely to have intentions to undergo breast cancer screening (aOR, 1.68; 95% CI, 1.28 to 2.19). In model 3, the full model, women with highly dense breasts (aOR, 4.17; 95% CI, 2.89 to 6.02) and with a higher level of knowledge on breast density (aOR, 1.65; 95% CI, 1.26 to 2.16) were significantly more likely to have intentions to undergo breast cancer screening. Women with private cancer insurance and a history of breast cancer screening within the past 2 years also more frequently reported having intentions to undergo breast cancer screening. Psychological measures, however, were no longer significant in Model 3.

In this study, we conducted a cross-sectional survey to assess awareness and knowledge of breast density among Korean women and the impacts thereof on psychological responses and intentions for future breast cancer screening. We discovered that only 38% of women were aware of their breast density status and that only 29.7% had a good level of knowledge on breast density (e.g., the masking effect of breast density on mammography test results and associations with breast cancer risk). Our results indicated that having awareness about one’s breast density status and having a good level of knowledge on breast density significantly increases perceived risk of and concerns for developing breast cancer by as much as 1.5-4 times. Furthermore, our results suggested that such psychological responses and breast density-related cognition boosted intentions to attend future screening tests.

Interestingly, ordinal regression analysis in this study revealed a significant association for awareness of breast density status with a higher level of perceived absolute and comparative risk and worry about breast cancer. Scores for these psychological reactions were significantly higher among women who reported that they had dense breasts. Additionally, perceived risk and cancer worry were significantly higher among women with a good level of knowledge on breast density. This trend was similar to that in previous studies showing that after informing women of their breast density status, they tended to show increased anxiety or psychological responses [12,13,17,18,24]. To be specific, Manning et al. reported that in a group of European American women, discovery of breast density status led to a higher perceived risk of developing breast cancer [10,11]. Another study conducted in Santiago indicated that after being informed of breast density status, perceived risk of breast cancer increased [11]. However, the opposite was observed among African American women with dense breasts who perceived themselves to be at lower risk, which could possibly be explained by race differences [10].

We also examined characteristics associated with differences in perceived risk and cancer worry. We discovered that Korean women aged 50-59 years of higher household economic status with a family history of cancer were more likely to have higher perceived risks of and greater concerns for developing breast cancer, as in previous studies [12,17]. Meanwhile, women with a high school education or greater were likely to have a higher perceived risk of developing breast cancer in their lifetime but were not greatly worried about developing cancer. Although the effect of perceived risk on screening intentions among women has remained somewhat unclear, it has been thought to be a facilitator for cancer screening attendance [11-13,25]. Our study demonstrated that intentions to undergo breast cancer screening were significantly greater among women with a high or very high perceived comparative risk. Meanwhile, concerns for developing breast cancer also had a positive impact on screening intentions, which is consistent with previous findings on perceived risk and worry in relation to screening behaviors [12,13,16].

Overall, we found that awareness and knowledge of breast density significantly boosted intentions to undergo screening within the next 2 years, consistent with a previous study in the United States [11]. This suggests that providing knowledge of a woman’s actual breast density status, as well as information on what effects breast density has, might positively influence screening intentions and might help promote an active role in decision-making processes to prevent breast cancer [10]. Notably, women with dense breasts had an odds ratio for intending to undergo future screening about four times higher than that in women without dense breasts or those not aware of their breast density status. This can be explained by the fact that women with dense breasts likely received much better explanations about their breast status and that the greater risk of developing breast cancer posed by a denser breast might have strengthened intentions to undergo breast cancer screening.

The prevalence of dense breasts among Asian women, including Korean women, is high, precisely 54.5% of Korean women aged 40-69 years, which is significantly higher than that in Western countries [20]. However, previous studies have reported that only a small proportion of Korean women get to know their own breast density status [10,11]: although women who have undergone mammographic screening through the NCSP are to be informed of their breast density status since 2007, the percentage of women who aware of their breast density status is only 38.2%. Moreover, as noted in the current study, women exhibited a lack of knowledge of the effects of a dense breast on mammographic sensitivity. Knowledge of these effects was especially low among women who did not know the density of their breasts. The majority of women who did know the density of their breasts had acquired knowledge on breast density from medical staff, while the other women had acquired information from their family members and acquaintances. This reflects the importance of a health professional in helping women understand breast density and the need for an efficient route for disseminating information on breast density to Korean women.

While a dense breast is considered a significant risk factor for breast cancer, there are some concerns as to which methods for classifying density are suitable for screening. The BI-RADS classification is the most widely used method for assessing mammographic density; however, its assessment is based on a qualitative method and is less effective than other methods, such as Cumulus [26]. In BI-RADS classification, the upper two classes reflective of a “dense” breast tend to show lower sensitivity in breast cancer screening and to increase the risk of false-negative mammography results, especially in older women [3]. This limitation imposes a need for high inter-radiologist agreement and more experienced and well-skilled radiologists in mammography reading [20]. Cumulus, a semi-automated thresholding method regarded as a gold standard, was developed to improve reproducibility and has a well-established relationship with cancer risk [27,28]. However, this method also requires trained observers, and the best threshold for separating dense tissue from fat is unclear [27]. Therefore, understanding the limitations of mammographic density measurements is essential when assessing the risk of breast cancer. More objective and quantitative breast density measures, combined with digital radiographic systems for mammography, should be implemented.

One of the strengths of our study is that it is the first study to describe an interrelated association between breast density awareness, breast density knowledge, and screening intentions among Korean women. Our findings can be generalized to Korean women aged 40 years and older, as the study samples were nationally representative. Despite these strengths, our study still has several limitations that should be considered. First, due to the nature of the cross-sectional study design, the ability to deduce causal relationships from the observed associations may be limited. Further studies with a qualitative or longitudinal design are recommended. Second, because the study data were obtained using a self-reported questionnaire, information bias may be present, and participants could have missed information related to their breast density awareness. Third, breast density information based on BI-RADS classification may be inaccurate due to low sensitivity and specificity of mammographic screening in Korea. Despite these limitations, notification of mammographic results indicating the presence of dense breasts would be of utmost importance, allowing clinicians to make prompt decisions or guidelines for women with high breast density, including suggesting them to undergo supplementary tests. In the long run, further study will be needed to determine whether giving an individual information on their breast density leads to reductions in the mortality rate of breast cancer.

In this study, we discovered positive associations for breast density awareness and knowledge with psychological reactions and screening intentions among Korean women. Currently, a large proportion of Korean women lack awareness of the density of their breasts and knowledge of the impact of breast density on breast cancer risk and detection. To encourage favorable screening behaviors, improvement of breast density, and knowledge through effective health communication between health professionals and women is recommended.