Very low mammographic breast density worsens the prognosis of breast cancer, according to a recent study published in European Radiology (2015; doi:10.1007/s00330-015-3626-2).
Disease-free survivals as well as overall life expectancies were significantly shorter in women with very low-density breasts in comparison to women with high-density breast tissue. The lower the breast tissue density, the less fibroglandular tissue there is compared to fat tissue.
In the future, these findings may prove significant for the assessment of breast cancer prognosis and treatment planning.
The study, conducted by researchers at the University of Eastern Finland in Kuopio, involved 270 breast cancer patients at Kuopio University Hospital, ages 32 to 86 years. Breast tissue density was analyzed on the basis of mammographic images obtained at the time of diagnosis.
The researchers determined the proportion of dense glandular tissue of the overall breast area. Breast tissue density was categorized as low when the proportion of glandular tissue was below 25%, and as very low when the proportion of glandular tissue was below 10%.
The study was a 6-year follow up focusing on the effects of breast tissue density and other mammographic features on breast cancer prognosis.
The results indicate that a very low breast tissue density is an independent poor prognostic factor of breast cancer, regardless of patients’ age, menopausal status, or body mass index. Of the women with very low breast tissue density, 70.7% were alive at the end of the 6-year follow-up, whereas 87.7% of women whose proportion of glandular tissue was higher than 10% were alive at 6 years. Lower breast tissue density was also associated with more aggressive higher-grade tumors.
The results are particularly interesting because dense breast tissue has long been known to be associated with an increased risk of cancer.
“It is difficult to detect small tumors when screening dense breasts, and this results in a higher occurrence of clinically detectable interval cancers. In the United States, informing patients if they have dense breast tissue is now mandatory. This allows them to choose whether they wish to have further tests, for example a screening ultrasound,” says Professor Ritva Vanninen, MD, PhD, of the University of Eastern Finland.
“It could be assumed that dense breast tissue would also be associated with a poorer prognosis in patients with a recently diagnosed breast cancer. However, this was not the case in our study, as low breast tissue density specifically weakened the prognosis.”