The first of these studies compared the sensitivities of mammography, ultrasonography, MRI and BSGI for detecting invasive lobular carcinoma (ILC). The research team - headed up by Rachel Brem, director of breast imaging and intervention at George Washington University Medical Center (Washington, DC) - performed a retrospective review of 26 women with biopsy-proven ILC, all of whom had undergone mammography and BSGI (AJR 192 379).
The mammography and BSGI imaging findings were classified by experienced breast imagers as positive or negative for ILC. Where performed, ultrasound (25 patients) and MRI (12 patients) results were also examined. The researchers concluded that BSGI was the most effective diagnostic imaging technique, with a sensitivity of 93%. Mammography, ultrasound and MRI demonstrated sensitivities of 79%, 68% and 83%, respectively.
"The study is significant because ILC can often be difficult to detect mammographically and is often not palpable at clinical examination," Brem explained. "BSGI offers improved detection of this form of breast cancer that impacts approximately 10% of new breast-cancer patients every year."
To perform BSGI, the patient is given a radioactive tracing agent. The gamma-ray emission from this radiotracer is then used to form a digital image showing the metabolic activity of the breast tissue. Due to their higher metabolic rate, cancerous cells absorb more tracer than healthy cells and thus appear as "hot spots" on a BSGI image.
"BSGI is a physiologic, rather than an anatomic, approach to breast-cancer diagnosis," said Brem. "It is likely that the molecular imaging obtained with BSGI is the reason it has the greatest sensitivity for the detection of ILC. In fact, it is known that MRI can be limited in the detection of ILC. In addition, the cost of BSGI is significantly less than a breast MRI."
Extended view
Elsewhere, a research study led by Nathalie Johnson, general surgeon and surgical oncologist at Legacy Good Samaritan Hospital (Portland, OR), demonstrated that BSGI can reveal additional cancers in patients newly diagnosed with breast cancer (Am. J. Surg. 197 159).
Johnson and her team conducted a retrospective review of 138 breast-cancer patients (69 invasive ductal carcinoma, 20 ILC, 32 ductal carcinoma in situ, and 17 mixed) in whom BSGI was performed as part of the imaging work-up. BSGI detected additional or more extensive malignancy in the same or opposite breast in 10.9% of these patients. The positive predictive value for BSGI was seen to be 92.9%.
According to Johnson, the biggest benefit of BSGI over breast MRI (often used as a mammography adjunct) is its specificity. "The sensitivity of BSGI is on par with MRI, but the specificity is higher. In addition, when compared to MRI, BSGI is less expensive and easier to use for patient and physician."
She continued: "The research is important because it helps clarify the role of BSGI in newly diagnosed breast-cancer patients. We have found that these women can have more extensive disease that is not detected by mammography or ultrasonography. This is especially helpful in patients with dense breast tissue where additional evaluation of the remaining breast tissue is necessary."
In both studies, BSGI was performed with the Dilon 6800 Gamma Camera, a high-resolution, compact field-of-view gamma camera, optimized to perform BSGI. According to its manufacturer Dilon Technologies (Newport News, VA), the camera provides a manageable four to 16 images, compared with up to thousands of images generated with breast MRI.