Breast gamma imaging demonstrates detection strength
The utilization of breast specific gamma imaging (BGSI) demonstrated a higher sensitivity in the detection of invasive lobular carcinoma than mammography, MRI, or ultrasonography, according to the results of a recent multi-center retrospective study.

“Invasive lobular carcinoma is the second most common breast malignancy, accounting for approximately 10 percent of breast cancers,” wrote the authors of the study, published in the American Journal of Roentgenology (February 2009). “Arising from the lobular epithelium, invasive lobular carcinoma tends to be insidious in onset because it does not invoke a vigorous desmoplastic response. Its incohesive histologic growth pattern, low likelihood of producing calcifications, and low opacity may account for the fact that invasive lobular carcinoma is frequently not apparent mammographically and is difficult to identify clinically.”

Breast images of 57-year-old woman with biopsy-proven lobular carcinoma in situ of left breast and invasive lobular carcinoma in right breast, about which findings from all imaging techniques agree. Sonogram of right breast shows hypoechogenicity (cursors) with ill-defined margins in upper outer quadrant. Breast-specific gamma image of right breast in mediolateral oblique projection also shows intense focus of uptake. All findings are concordant with biopsy-proven invasive lobular carcinoma. Images and caption courtesy of the American Roentgen Ray Society.
The study was performed as a multicenter retrospective chart review from four institutions: two academic centers and two private practices. All results and data were obtained solely from patients’ medical records. Only women with biopsy-proven pure invasive lobular carcinoma who also underwent BSGI were eligible for inclusion in the study group.

The study group included 26 women ranging in age from 46 to 82 years (mean age, 62.8 years) with a total of 28 biopsy-proven invasive lobular carcinomas. All patients had undergone mammography and BSGI, and the imaging findings were classified as positive or negative for invasive lobular carcinoma by experienced breast imagers. The results of MRI and sonography, if either was performed, were included.

The mean pathologic size of the invasive lobular carcinomas was 22.3 mm (range, 2–90 mm), according to the researchers.

The BSGI camera (Dilon Technologies) uses a detector mounted to an articulating arm so that the breast can be imaged in all projections, including those comparable to the positions used in mammography. Patients were injected with 99mTc sestamibi in an antecubital vein prior to BGSI, and images were acquired with the system in the craniocaudal and mediolateral oblique projections.

“The number of counts per image varies from patient to patient depending on the uptake of sestamibi in the breast tissue; however, a minimum number of 100,000 counts per image were obtained,” the authors noted.

The scientists reported that mammograms were negative in six of 28 patients, yielding a sensitivity of 79 percent. In the 25 patients who underwent sonography, 17 had focal hypoechoic areas, yielding a sensitivity of 68 percent. In the 12 patients who underwent MRI, the sensitivity was 83 percent. BSGI had a sensitivity of 93 percent.

“Notably, in six instances in which the cancer was not seen on mammography, BSGI detected invasive lobular carcinoma lesions,” the authors wrote. “In addition, MRI detected four lesions that were missed on mammography. Statistical analysis did not show a statistically significant difference in invasive lobular carcinoma detection between BSGI and mammography, sonography, or MRI. However, a non-statistically significant trend toward improved detection using BSGI and MRI was seen, but additional and larger studies are needed to further investigate these trends.”

The clinicians also noted, from their experience, that the cost of a BSGI exam is less than half of a breast MRI exam and that results interpretation is quicker for BSGI than for MRI studies.

“Finally, with the increasing concern of renal complications with the administration of gadolinium, the IV injection of 99mTc sestamibi has not been reported to be associated with significant complications,” they observed.