Asymmetric Dense Breast is an Independent Breast Cancer Risk Factor

Research Article

Asymmetric Dense Breast is an Independent Breast Cancer Risk Factor

Alikhassi A¹*, Shariatalavi R¹ and Moradi B²

¹Department of Radiology, Cancer Institute, Imam Khomeini Hospital, Tehran University of Medical Sciences, Tehran, Iran

²Department of Radiology, Advanced Diagnostic and Interventional Radiology Research Center, Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran

*Corresponding author: Afsaneh Alikhassi, Department of Radiology, Cancer Institute, Imam Khomeini Hospital, Tehran University of Medical Sciences, Tehran, 3314114197, Iran

Received: April 20, 2021; Accepted: May 11, 2021; Published: May 18, 2021


Objectives: There are multiple known breast cancer risk factors, but most women with breast cancer do not have any of them, so there should be some other unknown risk factors. We hypothesized that asymmetric breast densities could be another breast cancer risk factor.

Method: In this study, we defined two case and control groups with 136 women with breast cancer and 136 who did not have breast cancer, respectively. Any different type of asymmetry in either breast was recorded in both groups.

Result: The frequency of focal asymmetry in cases was 47 (34.6%), which was statistically more significant than in the control group (28 (20.6%)) (p=0.010). There were three (2.9%) and five (3.7%) global asymmetries in the case and control groups, respectively (p=0.735). The frequency of one view asymmetry in the case and control groups was not significant (16 (11.8%) and 9 (6.6%) respectively) (p=0.142). In the case group, 59 (43.4%) women had at least one type of asymmetry, compared to 41 (30.1%) in the control group (p=0.02). We identify focal asymmetries (likelihood ratio, 1.215; p=0.027) is risk factors for breast cancer.

Conclusion: Breast density asymmetry is a breast cancer risk factor that could be scored, thus enhancing risk stratification for screening and prevention.

Keywords: Predictive factors of cancer; Asymmetric dense breast; Mammographic breast density


Breast cancer is the most common cancer among women, and mammography is the main modality of breast cancer screening [1]. Mammographic Breast Density (MBD), which reflects the amount of fibroglandular tissue, is an independent risk factor of breast cancer, and women with MBD of 75% or more have four to six times greater chance of developing breast cancer than women with MBD of ≤10% [2,3]. MBD can mask cancer on mammography and lower sensitivity [4].

In the most recent version of the ACR BIRADS reporting system, the percentage density is no longer used, and the type of breast composition is stressed. The sensitivity of mammography for noncalcified lesions decreases as the BI-RADS breast density category increases [4].

We hypothesis that the phenotype of mammography could be a risk factor for breast cancer. By this, we mean that breasts with more asymmetric fibroglandular tissue have more chance of future cancer. Not only the amount of breast tissue, but also the pattern of breast tissue are breast cancer risk factors. Asymmetry represents unilateral deposits of fibroglandular tissue not conforming to the definition of a mass.

The goal of our study was to determine whether asymmetric breast density is associated with breast cancer.


We conducted a case-control study among women referred to Imam Khomeini Hospital in Tehran University of Medical Science, which consist of known cases of breast cancer and healthy non-cancer patients who were referred for 2D digital screening mammography. This study was approved by the ethical committee of the Tehran University of Medical Science with the reference number of IR.TUMS. IKHC.REC.1397.281.

One-hundred-thirty-six women with breast cancer who were referred to our hospital were randomly selected as the case group and 136 who did not have breast cancer were considered as the control group and matched for age, breast density and menopausal status. In this study, the breast cancer group was those patients who had a confirmed pathology of breast cancer after tissue sampling. The median time from index mammogram in the case group to diagnosis for breast cancer was 1 to 2 years.

Exclusion criteria were previous history of surgery, biopsy, or hormone therapy. Written informed consent was taken from all the included patients to use their mammography information without declaring their personal data. Mammographies of all patients were reviewed by two radiologists with breast subspecialty who were blind to the assignment of patients to the case and control groups.

Any type of asymmetry in either breast, according to the last version of ACR BIRADS [4], was documented in case and control groups by both radiologists separately and in case of any disagreement, it was discussed and recorded: asymmetry was considered an area of fibroglandular tissue visible on only one mammographic projection; global asymmetries were those asymmetries consisting of an asymmetry over at least one-quarter of the breast; focal asymmetries referred to non-symmetrical density that was visible in both of the mammogram standard views and that did not have the characteristics of the mammary mass; and developing asymmetries those that were new, larger, and more conspicuous than on a previous examination (Figure 1 and 2).