Breast-specific gamma imaging targets hard-to-detect cancers

A relatively new small field-of-view gamma camera has proved promising for two of the most hard-to-detect breast cancers: ductal carcinoma in situ and invasive lobular carcinoma.

Dr. Rachel Brem and colleagues from the radiology department at George Washington University evaluated 117 breast cancer patients scheduled for biopsy with breast-specific gamma imaging, also known as molecular breast imaging (MBI). They used the Dilon 6800 Gamma Camera, a compact high-resolution anatomy-specific scanner, and the radiotracer technetium-99m sestamibi.

Patient noted palpable nodule four years post-lumpectomy and ductal carcinoma diagnosis. Mammogram shows no evidence of mass. Breast-specific gamma imaging reveals highly contrasting foci, which correspond to previous biopsy site. Histopathology confirms infiltrating lobular carcinoma. (Provided by Dilon)

Brem reported the findings at the March annual meeting of the National Consortium of Breast Centers in Las Vegas.

In one study, researchers designed the gamma camera to look specifically for ductal carcinoma in situ, which often manifests on mammograms as microcalcifications and can be more extensive than indicated on a mammogram. MBI identified 12 of 13 women with DCIS, resulting in a 92% sensitivity. The pathologic size ranged from 1 mm to 22 mm. The authors were encouraged at the detector's ability to reveal cancer smaller than 1 cm.

In the second study, Brem and colleagues tested the ability of MBI to detect invasive lobular carcinoma, which can often be missed on mammography because it does not form calcifications and has no well-defined mass, she said.

Researchers classified the images with numbers:

• 1. normal

• 2. benign with minimal patchy physiological uptake

• 3. probably benign with scattered patchy uptake

• 4. probably abnormal with mild focal radiotracer update

• 5. abnormal with marked focal radiotracer uptake

Of the 117 women, five (4.3%) had lesions that on pathology were found to be pure invasive lobular carcinoma, ranging in size from 15 mm to 60 mm. All five lesions had MBI studies that were classified as 4 or 5, with no false negatives.

"Breast-specific gamma imaging is a highly sensitive modality in detecting invasive lobular carcinoma, a cancer that is often difficult to detect mammographically, with ultrasound, or with physical examination," Brem said.

Dr. Ellen Mendelson, medical director of breast imaging at Northwestern Memorial Hospital in Chicago, said that MBI may be a good intermediate imaging modality between screening sonography and MRI.

"It's less expensive than MRI, the sensitivity is high, and the negative predictive value is nearly 100%," she said. "That is important. You want to know that you can rely on a study to exclude cancer."

For more information from the Diagnostic Imaging archives:

Adjunctive breast imaging modalities come up short

Breast imaging technique zeros in on subcentimeter lesions

Technique adds dimension to nuclear mammography

Scintigraphy/mammography combo could replace biopsy for developing countries