Spotlight: Breast-specific gamma imaging finds more cancer than mammo

Molecular breast imaging, also known as breast-specific gamma imaging (BSGI), was found to be significantly more sensitive compared to mammography. In fact, BSGI found lesions in 4 percent of women who received a clean bill with mammography, according to a meta-analysis published online by the European Journal of Nuclear Medicine and Molecular Imaging.

Yu Sun, MD, a research scientist from the department of breast surgery at the Guangxi Cancer Hospital and affiliated Cancer Hospital of Guangxi Medical University, and colleagues, reviewed 19 papers involving imaging studies of a total of 3,093 patients in a retrospective study reviewing BSGI as a supplement to mammography for diversified detection of breast cancer.

In all studies, the breast-specific gamma camera was used in conjunction with injection of either Tc-99m sestamibi or tetrofosmin, both mitochondria-avid radiotracers. Higher density of mitochondria strongly implies spots of increased cellular proliferation and angiogenesis in breast tissue. In general, functional imaging rather than anatomical imaging of the breast bypassed tissue density, scarring and other limitations of mammography. Compared to conventional gamma cameras, breast-specific gamma imaging provided higher intrinsic spatial resolution, less proximal organ scatter and better imaging of medial and posterior breast regions.

BSGI could be more comfortable for patients, as it involves less compression than mammography and acquires image data within five to 10 minutes, according to a May 1 release focused on the research.

Authors of this study concluded that BSGI detected 95 percent of cancers of the breast. Areas of strength for the modality included imaging dense breasts and detecting lobular carcinoma, which was imaged with BSGI with 93 percent sensitivity, as well as early stage ductal carcinoma in-situ (DCIS). This type of cancer was captured with 88 percent sensitivity compared to mammography, which had a sensitivity range from 27 to 82 percent.

“The results of this meta-analysis indicated that BSGI has an excellent diagnostic performance as an adjunct modality to mammography for identifying breast cancer with high sensitivity and moderate specificity,” wrote Sun et al.

Diminutive tumors were detected more readily than with mammography, particularly those smaller than 1 cm. “With increasing diameter of the breast cancer from less than 20 mm to more than 50 mm, the 5-year survival rate decreased from 96.3 percent to 82.2 percent in patients with node-negative disease,” wrote the researchers. “So it is important to find an effective examination technique for detecting small cancer to achieve early detection and early treatment. In our analysis, BSGI showed a sensitivity for detecting sub-centimeter breast cancer of 84 percent, and the smallest carcinoma identified by BSGI was 1 mm.”

A comparison of BSGI to breast MRI showed similar sensitivity, but superior specificity, 80 percent, for BSGI. Cost of BSGI imaging was markedly less than breast MRI--approximately one third the procedure price. Like MRI, imaging the breast with dedicated molecular imaging detected more cancer in about 6 out of 100 patients found to have a lesion after both ultrasound and mammography scans, without risk of contrast-induced complications.

For this meta-analysis, a variety of BSGI studies completed from 2004 to 2012 were compiled into bivariate analysis to evaluate the sensitivity, specificity and positive likelihood, negative likelihood and diagnostic odds ratios for each lesion with 95 percent confidence intervals. With these data, researchers devised a summary receiver operating characteristic curve to evaluate BSGI compared to mammography and other modalities used for breast cancer detection.

False-positive scans with BSGI were mostly attributed to benign growths, fibrocystic changes and fibroadenoma. False-negative lesions were either or both invasive ductal carcinoma or less than 1cm in size. Other caveats of the modality included difficulties in imaging close to the chest wall and for detecting axillary node involvement.

BSGI was shown to successfully classify 15 patients during chemotherapy and hormone therapy monitoring prior to undergoing breast surgery in one study and in another, positive biopsy rates were improved from 14 percent with mammography to 42.3 percent with BSGI. The authors indicated that biopsy determination based on BSGI findings could potentially reduce unnecessary biopsies.

The researchers recommended that BSGI be presented as a adjunct to mammography rather than a replacement despite BSGI’s superior sensitivity and specificity, mostly due a lack of research regarding BSGI and patient survival and increased radiation dose with BSGI compared to mammography. They estimated that BSGI involves a dose range from 6.29 to 9.44 mSv, whereas  mammography ranges from 0.7 to 1.0 mSv. The authors indicated that improvements in detector technology in time could potentially cut down on radiotracer-associated radiation dose.