For breast cancer survivors, is there a correlation between dense breasts and the likelihood of cancer in the opposite breast?

Yes. There is a 1.8-fold higher risk of cancer in the opposite breast among women with dense breasts [1], but density and associated risk can be reduced with treatment. A 10% decrease of mammographic density or more within the first two years after an original diagnosis, as a result of treatment, is associated with a significantly reduced risk of cancer in the opposite breast (known as contralateral breast cancer) [2]. This potential new risk predictor can thus contribute to decision-making in follow-up treatment – particularly the continuation of a chemoprevention drug, like tamoxifen or aromatase inhibitors, which reduce breast density in some women [3].