A study found that a relatively new type of breast imaging, breast-specific gamma imaging (BSGI), is better than ultrasound at finding breast cancer when a screening mammogram shows a suspicious area. These results were presented at the 2010 American Society of Clinical Oncology (ASCO) Breast Cancer Symposium.
When doctors can't tell if an area on a mammogram is cancer or not, the result is called indeterminate. In these cases, doctors often recommend a breast ultrasound to help decide if the area is cancer or not. About 10% of all mammogram results are indeterminate and require a woman to have more tests. Indeterminate mammogram results are more likely in women with dense breasts. Dense breasts have less fatty tissue and more non-fatty tissue compared to breasts that aren't dense. This can make mammograms harder to read.
While breast ultrasound can be helpful when a mammogram is indeterminate, an ultrasound can still miss finding cancer. An ultrasound also may suggest that a suspicious area is cancer when it's not. This is called a false positive. Doctors also may recommend other imaging tests, such as breast MRI, to help decide if an area is cancer. And even after all these imaging tests, some women still will need to have a biopsy to know for sure if an area is cancer.
BSGI uses a radioactive tracing substance to detect cancer. The tracer is taken up by both healthy and cancer cells. But because cancer cells are growing and dividing more and faster than healthy cells, the cancer cells tend to take up more tracer. After the tracer is injected, the breast is scanned with a machine that detects the radioactivity of the tracer. A concentrated amount of tracer in part of the breast suggests cancer.
In this study, researchers looked at ultrasound and BSGI results in 111 women with indeterminate screening mammograms. To make sure the evaluations were consistent, all the imaging tests were reviewed by the same doctor. All the women had a biopsy of the suspicious area, so the researchers knew how accurate both the ultrasound and BSGI results were. Biopsy results were reported as:
- high-risk (not cancer, but with the potential to become cancer)
The researchers found that BSGI was much better at detecting cancer than ultrasound:
- BSGI correctly identified ALL the suspicious areas as cancer that were cancer.
- Ultrasound identified only 47% of the suspicious areas that were cancer. The other 53% of the cancers were incorrectly identified as high-risk or benign.
Like screening mammograms, both BSGI and breast ultrasound can have false positive readings. Still, false positives were less likely with BSGI than with breast ultrasound:
- 20% of the suspicious areas identified as cancer by BSGI weren't cancer
- 33% of the suspicious areas identified as cancer by breast ultrasound weren't cancer
Some doctors are concerned that because BSGI uses a radioactive tracer, the radiation exposure might cause cancer. Using math models to calculate this risk, the researchers concluded that the risk of radiation exposure from the BSGI tracer was very small. This slight risk was far outweighed by the benefits of accurately diagnosing breast cancer in women with indeterminate mammogram results.
Right now, BSGI is considered an experimental test. While more research is needed, these results suggest that BSGI could be helpful in diagnosing breast cancer.
Stay tuned to Breastcancer.org Research News to learn about new results that could lead to better ways to prevent, detect, diagnose, and treat breast cancer.