Getting Specific — Molecular Breast Imaging Seeks to Speed Diagnosis and Reduce False-Positives
By Kathy Hardy
Vol. 13 No. 2 P. 30
After a cancerous lump was discovered and removed from her left breast in 2008, then 25-year-old Shelley Barnes received an early education about the specifics of breast cancer, including detection methods. One lesson involved learning the balancing act that exists between imaging modalities with the sensitivity to locate questionable lesions in breast tissue and those with the specificity to determine the severity of those lesions.
Ultrasound and MRI were used in conjunction with mammography when Barnes was first diagnosed with breast cancer. When the disease struck again, this time in 2010, the young systems analyst for a Washington, DC, law firm benefited from the addition of breast-specific gamma imaging (BSGI) to her screening regimen. BSGI screening had been introduced after her first breast cancer diagnosis. This time, the cancerous mass in her left breast was detected in its early stages by BSGI.
“Without BSGI, I never would have known that I had cancer the second time,” Barnes says. “I would have gone another year without a screening. You don’t know how large the growth would have been by then. With BSGI, it was discovered and treated early.”
In both of Barnes’ bouts with breast cancer, the mass was neither visible in a mammogram image nor detectible during self-examination.
Breast imagers and surgeons are finding more instances where BSGI adds a level of peace of mind for women, particularly those with indeterminate mammogram results. This modality, also known as molecular breast imaging (MBI), images the metabolic activity of breast lesions by utilizing radiotracer contrast and a high-resolution gamma camera. They believe that using a physiological approach to breast cancer detection allows for more specific evaluations and improved management of challenging cases.
For Jean Weigert, MD, FACR, director of women’s imaging for the Hospital of Central Connecticut, BSGI is a vital diagnostic tool used in conjunction with other modalities. A recently completed clinical study of more than 1,000 patients that she presented at RSNA 2011 looked at how BSGI’s gamma camera capabilities play a role in early breast cancer detection by adding improved specificity to the sensitivity of breast cancer screening and diagnosis.
“With BSGI, you can be comfortable that what you’re seeing is something that needs to be acted on,” she says. “There’s also the issue of what you don’t see with BSGI. For the patient, both aspects of this technology are important due to the reduction in false-positive findings.”
Another clinician involved in the study, Lillian Stern, MD, director of breast imaging at Methodist Hospital in Philadelphia, agrees about the importance of not only discovering what is in the breast but also what isn’t there. “When a patient feels something but nothing shows up on a mammogram, they wonder if there’s really something there or not,” Stern says.
Weigert is first author on the study comparing BSGI with mammography and ultrasound. The study showed that BSGI had greater sensitivity and comparable specificity with ultrasound and diagnostic mammography. In addition, this technology is a valuable adjunctive procedure when these anatomical imaging modalities fail to provide a confident diagnosis. BSGI is also a useful diagnostic modality to augment mammography to manage patients with difficult-to-diagnose breast tissue and in cases where unresolved clinical concern remains after a mammogram.
“This study helped show the power of BSGI, especially in patients with indeterminate results on mammography or ultrasound,” Weigert said in a press release regarding the presentation. “Many suspicious areas can show up on ultrasound. BSGI helps us focus on the areas of true positive and determine where to biopsy.”
For this study, BSGI was conducted with the Dilon 6800, a high-resolution gamma camera. To perform BSGI, a patient receives a pharmaceutical tracing agent that emits gamma radiation after it is injected and absorbed by all the cells in the body. Due to their increased rate of metabolic activity, cancerous cells in the breast absorb a greater amount of the tracing agent than normal, healthy cells and generally appear as dark spots on the BSGI image.
Efforts are under way to try to reduce the radiation dose used in the contrast injection, Stern says. Dose tends to be an issue when it comes to molecular breast imaging, but she notes that the radiation dose from BSGI is similar to what the FDA has approved for use with cardiac stress tests and CT scans.
“The dose to breast tissue is low,” Weigert adds. “When looking at contrast, you need to consider the whole body.”
Weigert, who first used a gamma camera in 2005, notes several instances in which BSGI helped determine where to biopsy in women who received indeterminate mammograms. Even after follow-up screening ultrasound exams, she still wasn’t sure where to perform the biopsy. That’s where BSGI came in. She was impressed from the start, using the technology with approximately 800 patients from 2005 to 2007, with favorable comparisons made between BSGI results and ultrasound as a follow-up to mammography. Even simple marker lesions can be detected with BSGI, she says.
She cites two cases in that time where patients had no risk factors for breast cancer but showed “something that didn’t look right” in each of their ultrasounds. Using BSGI, she could see a “definite focus of abnormality.” She was able to biopsy those areas and make an accurate diagnosis.
“These women had no positive lymph nodes,” Weigert says. “I don’t know how long it would have taken to discover their breast cancer. There was nothing palpable in their earlier exams.”
In another case, gamma imaging actually clarified a woman’s diagnosis for a more favorable outcome.
“We found something, but we were able to determine that it was negative,” she says. “That’s reassuring for patients. When I can tell them that we didn’t see anything on the gamma, I can be 97% certain that it’s normal.”
In addition to women with indeterminate mammograms, Stern sees several other areas where using BSGI is effective. For example, if a patient could benefit from a breast MRI but cannot enter the magnet for whatever reason—whether she has metal in her body, such as a pacemaker, or she is claustrophobic—she could safely undergo BSGI. Stern also says that in some cases a patient’s insurance is more likely to cover BSGI than MRI.
Another area where BSGI is being used over other modalities is in patients who already had breast surgery. Mammography images will show scar tissue as something unusual; however, scars should no longer be visible one year after surgery.
“BSGI is helpful to use if something shows up one year after surgery,” Stern says. “It will help determine whether or not less concerning things that appear on a mammogram need biopsy.”
BSGI has a high sensitivity for ductal carcinoma in situ and lobular carcinoma, she notes, referring to these as the “sneaky” breast cancers due to greater detection difficulties. Both cancers can masquerade as normal tissue in standard mammography.
From a surgical perspective, BSGI helps clarify the view concerning where to biopsy; the device also includes a biopsy tool. According to Christine Teal, MD, FACS, chief of breast surgery at The George Washington University Hospital in Washington, DC, BSGI is useful in surgical planning as well.
“I can consult with other physicians, look at images on paper, show patients the extent of the disease, and then discuss a plan of action,” she says. “Patients can receive their results immediately.”
Teal, who was the surgeon for both of Barnes’ lumpectomies, says BSGI is helpful for screening women at high risk of breast cancer; it was determined after Barnes’ initial cancer diagnosis that she has dense breast tissue, a high-risk characteristic. However, she has no family history of the disease. Overall, Teal says she has seen “impressive numbers” in identifying cancers in asymptomatic patients such as Barnes.
“If a woman’s mammogram is indeterminate and there’s something that looks like dense breast tissue, we can use BSGI to find out for sure,” Teal says. “In Shelley’s case, she was on a schedule to receive regular BSGI screenings, and that’s how her second cancer was found.
“I don’t understand why BSGI isn’t used on a more widespread basis,” Teal adds. “We’re the only facility in the DC area using it. There is enough data that shows that BSGI is at least equal to MRI in detecting cancers and in some cases is better in that there are fewer false-positives.”
While breast MRI is used to screen high-risk women, Weigert said many physicians don’t want to use MRI in indeterminate patients because of that modality’s high sensitivity but lower specificity. There is a likelihood of more false-positives with MRI, as the technology is more sensitive but doesn’t provide the specificity of other modalities. That leaves BSGI as a potential alternative to ultrasound or MRI for breast evaluation after an indeterminate mammogram.
“I don’t think MRI is the way to go with indeterminate patients,” Weigert says.
On an MRI, many different things “light up,” Stern says.
“You need to discount many of the things that you see in an MRI,” Stern adds. “With BSGI, you can more clearly see these things and tell whether they are positive or negative.”
Another factor when considering modalities involves ease of use. In general, physicians find that gamma imaging is less time consuming and more patient friendly compared with MRI and more in line with ultrasound costs. According to Teal, BSGI comes in at one-tenth the cost of MRI.
“MRI is more complicated to do,” Weigert says. “There are issues with patient movement and claustrophobic patients, and the images are harder to interpret. Reading gamma images is like reading a mammogram.”
Those involved agree that MRI should not be ruled out but that all viable options should be considered.
“If, after a follow-up ultrasound, we’re still not sure, we could order an MRI,” Stern says “However, we have a better chance of approval for BSGI, and the latter is also more comfortable for the patient.”
From a patient-comfort perspective, Barnes says BSGI is most similar to undergoing a mammogram, just with a contrast injection, compared with ultrasound and MRI.
“You still have to place your breast between the plates like you do with a mammogram, but the comfort level is not that bad,” Barnes says. “At George Washington, you can sit down during the procedure, which makes it a more comfortable process.”
Stern concurs with Barnes regarding what patients experience when undergoing BSGI. Women sit in a chair during the scan and can even watch TV. There is a contrast injection and, as with a standard mammogram, there is a plate that rests on the breast. However, there is no compression. The device takes four to six images, which are simple and easy to read, Stern says.
Possible Screening Tool
Barnes’ most recent BSGI exam took place in March 2011. She will continue to undergo gamma imaging on an annual basis, along with annual mammograms scheduled for the six months between each BSGI. She is comfortable with this staggered screening schedule and feels confident that this will keep her breast cancer in check.
“This test [BSGI] should be a part of a woman’s regular screening process if she has a history of breast cancer in her family or had breast cancer herself,” Barnes says.
While BSGI is still a diagnostic tool, radiologists and surgeons both agree that this modality should have a place in the breast cancer screening process, helping with both the detection and the successful removal of cancerous lesions from high-risk women. As Barnes learned, its specificity can provide a clear picture of what the future holds.
— Kathy Hardy is a freelance writer based in Phoenixville, Pennsylvania. She is a frequent contributor to Radiology Today.