Women for whom a breast MRI exam is recommended to supplement a screening mammogram and/or a breast ultrasound, but will not or cannot have an MRI, have an alternative choice. Breast-specific γ-imaging (BSGI) is a physiologic imaging modality that can detect subcentimeter and mammographically occult breast cancer with a sensitivity and specificity comparable to MRI. A study published in the Journal of Nuclear Medicine showed that BSGI increased breast cancer detection by 1.7% in women at risk compared to mammography alone.
This technology offers an alternative to the 10% to 15% of patients who cannot have MRI exams due to renal insufficiency, large body habitus, or other factors like implantable devices. A BSGI exam does not claustrophobia. Additionally, its cost is much less expensive than an MRI by up to half, according to principal investigator Rachel F. Brem, MD, Professor of Radiology, Director of Breast Imaging and Intervention, and vice chair of radiology at the George Washington University School of Medicine in Washington, D.C.
Data regarding the applications of BSGI for supplemental screening for women at increased risk of breast cancer are sparse. In part because of this, and because previous studies have shown that BSGI reliably detects mammographically occult breast cancers, the authors conducted a retrospective study to determine the incremental increase in breast cancer detection when BSGI is used as an adjunct to mammography.
BSGI is a nuclear medicine exam. A high-spatial resolution, small field of view γ-camera detects and localizes γ-ray energy emitted by the radiopharmaceutical 99mTc-methoxyisobutylisonitrile (sestamibi). Following intravenous injection, this radiopharmaceutical preferentially accumulates in malignant breast cells with increased vascular supply and concentration of mitochondria compared with surrounding normal breast tissues. Approximately 12 images or fewer are acquired between 6 and 10 minutes. The patient is seated for approximately 40 minutes, in standard mammographic views with the breast in mild compression.
The study included 849 patients at increased risk who had a BSGI examination (6800, Dilon Technologies, Newport News, VA) between April 2010 and January 2014. The patients ranged in age from 26 to 83 years. Half of the patients had a prior history of breast cancer, and 27% had a family history of the disease. Fifteen percent had two or more risk factors.
All exams were reviewed by three board-certified radiologists with 6 to 20 years of BSGI interpretation experience among them. Images were assigned a score of 0-5. Exams with an area of focally increased radiotracer uptake were classified as abnormal.
Two-hundred-twelve patients, or 25%, had positive BSGI exams. None of these patients had BRCA gene mutations, but 42% had a prior history of breast cancer and 31.6% had a family history. A total of 14 patients had mammographically occult BSGI-detected breast cancer. Eleven of these patients had heterogeneous or extremely dense breast tissue. The study found that BSGI detects 16.5 high risk lesions for every 1,000 at risk women.
The study also showed that more than half of detected cancers were small (less than or equal to 1 cm) invasive carcinomas or ductal carcinoma in situ. Five of the six invasive carcinomas were histologic grade 2 and 3, with two triple-negative cancers and one ancer positive for human epidermal growth factor receptor 2 gene amplification.
The authors pointed out that the primary disadvantage of BSGI was radiation exposure. In an accompanying invited commentary, Amy M. Fowler, MD, assistant professor of radiology in the Breast Imaging Section of the University of Wisconsin School of Medicine and Public Health in Madison, wrote: “Despite a strong diagnostic performance of BSGI, concerns regarding lifetime radiation exposure will likely impede its widespread adoption as a serial supplemental screening method….Continued research into dose reduction methods or consideration of less frequent screening intervals will facilitate broader acceptance of radionuclide-based supplemental screening approaches in clinical practice.”
Dr. Brem told Applied Radiology that breast cancer screening is becoming individualized, and that a recommendation for BSGI is individualized to the patient. “We do not do routine screening BSGI, or for that matter, other tests unless needed. In very high risk women, we use BSGI and MRI for surveillance. In women with dense breasts but no other risk factors, we would use screening ultrasound to supplement a screening mammogram.”
Asked why BSGI is not more commonly used, Dr. Brem said, “Many breast imaging physicians are not as comfortable with nuclear medicine examinations as they are with MRI. Frankly, I don’t know why BSGI is not more widely available. It is a cutting edge, wonderful technology that can find mammographically and sonographically occult cancers. It is not a difficult exam to interpret, and we have presented that interpreting BSGI exams require far less time than MRI exams. And having BSGI allows women to have physiologic imaging when they cannot or will not undergo MRI.”
BSGI: A comparable alternative to MRI breast cancer screening for at-risk women. Appl Radiol.