High-Risk Women: MRI Shows More Breast Cancer
Mammography, Ultrasound Often Miss Small Tumors
Sept. 14, 2004 -- For women with genetic risk, MRI is the best choice for breast cancer screening, a new study shows. MRI can detect small tumors often missed by mammography and ultrasound, researchers say.
Inherited genetic mutations in the genes BRCA1 and BRCA2 increase the risk of developing breast cancer, they are very rare and account for only 5%-10% of all breast cancers diagnosed in the U.S.
For most women, mammography is still considered the gold-standard screening for breast cancer. But for women with the BRCA1 and BRCA2 genes, studies have shown that mammography catches only 50% of all breast cancer tumors. However, another 50% of tumors develop between screenings.
Experts say that surveillance for breast cancer in these high-risk women should include monthly self-breast exam starting at age 20, semiannual breast exams by a health care professional staring between 20-35 years old, and annual mammograms beginning at 25 to 35 years old.
For other women, age 40 is the recommended age to begin to screen for breast cancer with mammogram.
For women with dense breasts tissue, MRI has proven to be a highly sensitive screening tool in detecting abnormalities Ultrasound also works well with these women -- although the results depend on operator experience, and there are often false-positives, writes researcher Ellen Warner, MD, a medical oncologist with Toronto-Sunnybrook Regional Cancer Center in Toronto, Canada.
Her study, which appears in this week's issue of the Journal of the American Medical Association, is the largest study to date of women with BRCA1 and BRCA2 mutations, Warner writes. A number of studies have also shown that MRI may be beneficial for high-risk women, but it has not been tested as a screening tool in women with BRCA mutations, she notes.
"MRI has emerged as an extremely powerful tool in breast cancer [detection]," writes Mark E. Robson, MD, with Memorial Sloan-Kettering Cancer Center, in an accompanying editorial. Warner's study "provides important new information for women at hereditary risk."
Warner's study involved 236 Canadian women aged 25-65 years old with BRCA1 or BRCA2 genetic mutations. All got up to three screenings yearly -- MRI, mammography, and ultrasound -- over a six-year period. Breast exams by health care professional were performed on the day of screening and at six-month intervals. Biopsies were performed if anything looked suspicious.
- A total of 22 cancers -- 16 breast cancer tumors and six precancerous tumors -- were detected.
- Clinical breast exam detected 9% of tumors, 36% were found through mammography, 33% by ultrasound, and 77% by MRI.
- 32% of cancers were detected by MRI but were missed by the other screening methods; 10% were detected by mammography alone and 10% by ultrasound alone.
In women with BRCA mutations, MRI was "significantly more sensitive" than either mammography or ultrasound -- detecting 75% of 12 cancers missed by the mammography and clinical breast exam.
As far as interpreting an imaging result as positive when subsequent tests show no cancer existed (false-positive results), mammography produced one in the first year, and none in subsequent years, Warner says. MRI produced more false-positive results -- but only in the first year's screening. In the second and third years, the rate was consistently lower than the ultrasound results.
This may be due to the operator's or radiologist's inexperience or because no previous MRIs were available for comparison, she explains. Also, the cancers could have grown so rapidly that, although undetectable in the first year, they were very detectable later.