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Breast Cancer Risk Linked to Bone Density

Testing Bone Density

Bone densitometry testing is primarily performed to identify persons with osteoporosis and osteopenia (decreased bone mass) so that the appropriate medical therapy and treatment can be implemented.

Early treatment helps to prevent future bone fractures. It may also be recommended for persons who have already fractured and are considered at risk for osteoporosis.

The bone densitometry test determines the bone mineral density (BMD).

Your BMD is compared to two norms - healthy young adults (your T-score) and age-matched (your Z-score).

First, your BMD result is compared with the BMD results from healthy 25- to 35-year-old adults of your same sex and ethnicity.

The standard deviation (SD) is the difference between your BMD and that of the healthy young adults.

This result is your T-score. Positive T-scores indicate the bone is stronger than normal; negative T-scores indicate the bone is weaker than normal.

According to the World Health Organization, osteoporosis is defined based on the following bone density levels:

  • A T-score within 1 SD (+1 or -1) of the young adult mean indicates normal bone density.
  • A T-score of 1 to 2.5 SD below the young adult mean (-1 to - 2.5 SD) indicates low bone mass.
  • A T-score of 2.5 SD or more below the young adult mean (> - 2.5 SD) indicates the presence of osteoporosis.

In general, the risk for bone fracture doubles with every SD below normal.

Thus, a person with a BMD of 1 SD below normal (T-score of -1) has twice the risk for bone fracture as a person with a normal BMD. A person with a T-score of -2 has four times the risk for bone fracture as a person with a normal BMD.

When this information is known, people with a high risk for bone fracture can be treated with the goal of preventing future fractures.

Secondly, your BMD is compared to an age-matched norm.

This is called your Z-score. Z-scores are calculated in the same way, but the comparisons are made to someone of your age, sex, race, height, and weight.

Always consult your physician for more information.

[October 2008] Calculating a woman's bone mineral density appears to shed light on her risk for breast cancer, says a report in the journal Cancer.

Picture of a female radiologist reading an x-ray

The study found that high bone mineral density predicts a greater likelihood of developing breast cancer - independent of how high a woman’s risk is on the often-used Gail model.

The Gail model incorporates information on family history, age, and other factors to estimate a woman's risk of breast cancer over five years and over her lifetime.

The model does not, however, include data on bone mineral density, which is known to be a risk factor for breast cancer.

The two measurements together might be used in tandem to better predict breast cancer risk, the researchers say.

Bone Health Gives Heads Up

The findings follow closely on the heels of other research linking different aspects of bone health with breast cancer risk.

One study presented at the American Society of Clinical Oncology meeting found that Zometa® (zoledronic acid), a medication used to treat osteoporosis, lowered the risk of breast cancer recurrence in premenopausal women.

And another study released this spring found that women with breast cancer who have a vitamin D deficiency at the time of their diagnosis were more likely to have a recurrence or to die from their disease. Vitamin D is also critical to bone health.

The new study incorporates Gail scores and hip bone mineral density information on almost 10,000 postmenopausal women participating in the Women's Health Initiative.

After an average of almost nine years of follow-up, women with a high Gail score were, overall, 35 percent more likely to develop breast cancer. And for each unit of increase in total hip bone mineral density, a woman's risk rose 25 percent.

There was a particularly high increase in risk for women with the highest bone mineral density and Gail scores.

Estrogen, Weight, and Bone - More to Learn

Women with high bone density often are overweight or obese, a condition which elevates their risk of breast cancer and which may well be the common denominator, says Dr. Jay Brooks, at Ochsner Health System in Baton Rouge, Louisiana.

"This is more information that shows a link in my opinion, between increasing weight, obesity, and the development of breast cancer," he adds.

But the picture for women remains a complicated one, another expert says.

"Even with these additional findings, however, it's still not clear what the precise relationships are between estrogen, bone density, and breast cancer," says Dr. Mary Daly, at the Fox Chase Cancer Center in Philadelphia.

Always consult your physician for more information.

 

  
 
Yale School of Medicine