CHICAGO – Two breast imaging technologies reported at the annual meeting of the Radiological Society of North America (RSNA; Oak Brook, Illinois) fill significant voids in cases where traditional mammography and MRI fail to accurately diagnose cancer.
Where mammography and ultrasound are anatomically oriented, these technologies are a form of molecular imaging. Up to 15% of breast cancers are not mammographically visible.
In the first study, scientists discussed how mammography and MRI usually work quite well, except for women with dense breast tissue or those with hormonal changes that occur regularly as part of the menstrual cycle.
Half of women under the age of 50 have dense breasts and breast density is a strong risk factor for breast cancer.
Enter a new adjunct for imaging the breast: positron emission mammography (PEM), which is not affected by either breast density or a woman's hormonal status.
"We've had the opportunity to work with PEM for the last two years," said lead researcher Kathy Schilling, MD, director of breast imaging and intervention at the Center for Breast Care at Boca Raton Community Hospital (Boca Raton, Florida). "It gives us great clarity and confidence in diagnosing cancer. These are for cancers we were unable to identify with other tools. The sensitivity of PEM is equal to or better than breast MRI, and PEM has fewer false-positive results."
Schilling showed films of PEM vs. mammography and the difference was stunningly obvious. The former was bright, crisp and clear. The latter was snowy and obviously would require seasoned eyes to spot the cancer.
Mammography, the standard screening tool for breast cancer, isn't as effective when breast tissue is less fatty and more glandular. For these women, doctors turn to breast MRI, particularly to screen women at high risk for breast cancer. But MRI has a high incidence of false-positive test results that indicate cancer is present when it is not. Some researchers think the false positives are due partly to hormonal changes that occur during a woman's menstrual cycle.
"Unless the MRI is performed on day seven through 14 of a woman's cycle, reading MRI images is extremely difficult," Schilling said.
She sought to explore another option for these outliers with PEM because hormones do not have the same effect on these test results. More specifically, Schilling thinks PEM could play a significant role both in preoperatively evaluating breast cancer patients and in screening high-risk patients.
In the study she presented at RSNA, 208 patients with breast cancer underwent PEM, an application of high-resolution breast positron emission tomography (PET) in which a small amount of radioactive material is injected into the body to measure metabolic activity and determine the presence of disease.
Researchers used a PET unit specially developed by Naviscan (San Diego) for the breast and small body parts to perform the PEM exam.
Of 189 malignant lesions imaged, PEM detected 176 for an overall sensitivity rate of 93%. Fifteen percent were ductal carcinoma in situ (DCIS), a noninvasive cancer confined to the ducts of the breast; 85% were invasive cancer.
PEM successfully detected cancer in 100% of fatty breasts, 93% of dense breasts, 85% of extremely dense breasts, 93% of women both with and without a history of hormone replacement therapy, 90% of pre-menopausal women and 94% of post-menopausal women.
Additionally, PEM allows women to sit upright, compared to the prostrate and strapped-down position women must submit to as they are rolled into the tube of an MRI machine.
When asked why PEM wouldn't simply replace mammograms and MRI for all breast cancer screening, Shilling told Medical Device Daily that it's not widely available. Naviscan is the sole manufacturer of the $850,000 device.
Last month, the company also reported that it had received FDA clearance for its biopsy-guidance feature designed exclusively for use with its PEM (MDD, Nov. 24, 2008).
Stereo Navigator, the PEM-guided biopsy accessory, is indicated for the localization of lesions in female breasts, as identified on a PET image.
The second breast cancer advance reported at RSNA is breast-specific gamma imaging (BSGI), considered effective in the detection of cancers not found on mammograms or by clinical exam. It relies on advanced gamma imaging technology and mammographic positioning to optimize result.
"BSGI materially changes the management of women with newly diagnosed breast cancer," Rachel Brem, MD, professor of radiology and director of the Breast Imaging and Interventional Center at the George Washington University Medical Center (Washington).
It's particularly accurate with the most difficult to detect breast cancer: invasive lobular carcinoma, according to the new study. There are 178,480 new cases of invasive breast cancer and 62,030 cancers in situ carcinoma of the breast diagnosed each year.
BSGI isn't new. The sole manufacturer, Dilon Technologies (Newport News, Virginia), received FDA approval in 1999 for the high-resolution gamma camera, the Dilon 6800 (MDD, June 11, 2008). The Dilon 6800 – which costs $250,000 – is located at 50 sites across the U.S. The technology has, in fact, been used for decades to image the heart.
Where BSGI differs from PEM is that PEM uses a much higher dose of radiotracer, Brem said, adding that a PEM dose is equivalent to three doses of mammography radiation and BSGI is half of that.
"We use this to screen high-risk women. With PEM, you already have to have a diagnosis," Brem said. "Also, PEM can't be done in diabetics. With BSGI, there is no impact on glucose levels."
In the newest study Brem reported, there were 159 women with one biopsy-proven cancer; of those 73% had dense breasts.
BSGI results showed an additional suspicious lesion missed by mammography and physical exam in 46 (29%) of the women. In 14 (36%) of the 39 women who underwent biopsy, the newly discovered lesions were cancerous. BSGI also detected 9% additional cancers either in the same or other breast and the smallest cancers detected were less than 1 cm.
There are numerous previous studies of BSGI. The novelty of Brem's study is that it showed BSGI is effective in finding additional cancers.
BSGI uses a high-resolution gamma camera that allows for imaging with very mild compression of the breast along with an injection of a low-dose nuclear material called a radiotracer, which is absorbed by the cells. Because cancerous cells have a higher rate of metabolic activity, the tracer is taken up by these cells at a higher level than in normal cells.
"The data suggest that BSGI allows for the diagnosis of more and earlier breast cancers," Brem said.