From the Guidelines
Breast size is not directly associated with an increased risk of breast cancer, but rather breast density is a known risk factor. Women with dense breasts, which can be more common in women with larger breasts, have a higher risk of developing breast cancer, with a relative risk of about 1.45 compared to those with scattered fibroglandular density 1. However, it's essential to note that breast size is just one of many factors that can influence breast cancer risk, and other significant factors include age, family history, genetics, lifestyle choices, and overall health. Regardless of breast size, all women should follow recommended breast cancer screening guidelines, which typically include:
- Monthly breast self-exams starting at age 20
- Clinical breast exams every 1-3 years for women in their 20s and 30s, then annually from age 40
- Annual mammograms starting at age 40-45 (or earlier if high risk) Women with larger breasts or dense breasts should be particularly vigilant about thorough self-exams and inform their healthcare provider if they have difficulty examining all breast tissue due to size or density. In some cases, additional imaging techniques like ultrasound or MRI may be recommended to ensure comprehensive screening 1.
From the Research
Association Between Breast Size and Breast Cancer Risk
- The relationship between breast size and breast cancer risk has been investigated in several studies, with some suggesting a positive association, particularly among lean women 2, 3.
- A study published in 1999 found that breast size, as measured by bra cup size, was a significant risk factor for postmenopausal breast cancer among women who were lean as young adults, with a multivariate-adjusted relative risk of 1.34 for cup size B and 1.76 for cup size C and larger, compared to a cup size smaller than B 2.
- Another study published in 2006 found that larger bra cup size at a young age was associated with a higher incidence of premenopausal breast cancer, although this association was limited to leaner women with a BMI below 25 kg/m2 3.
- A systematic review of 50 papers published in 2014 found that increasing breast size appears to be a risk factor for breast cancer, although the evidence is limited by the retrospective nature of the studies and the presence of confounding variables 4.
- However, not all studies have found a significant association between breast size and breast cancer risk, and the relationship between the two is likely to be complex and influenced by a range of factors, including BMI, menopausal status, and mammographic density 5, 6.
Mammographic Density and Breast Cancer Risk
- Mammographic density has been shown to be a strong risk factor for breast cancer, with studies suggesting that women with higher levels of mammographic density are at increased risk of developing the disease 5, 6.
- A study published in 2006 found that BMI and mammographic density are independent risk factors for breast cancer, and that the strong negative correlation between them can lead to underestimation of the effects on risk of either pathway if confounding is not controlled 5.
- A more recent study published in 2024 found that women who maintain higher levels of mammographic density over time, or who experience an increase in mammographic density, are at higher risk of subsequent breast cancer than women who experience a decline in mammographic density over time 6.
Limitations and Future Directions
- The current evidence on the relationship between breast size and breast cancer risk is limited by the retrospective nature of many studies and the presence of confounding variables 4.
- Further research is needed to fully understand the relationship between breast size, mammographic density, and breast cancer risk, and to determine the clinical implications of these findings 2, 5, 6, 4, 3.