Mammoscintigraphy, Sentinel Node Biopsy ‘Here to Stay’

TOWSON, Md—Mammoscintig-raphy and sentinel node radiolocaliza-tion, “both hot topics at the leading edge of breast imaging,” are increasingly appropriate in the diagnosis and care of breast cancer, said Carlo Ludovico Maini, MD, director of nuclear medicine, Regina Elena National Cancer Institute, Rome, Italy.

“Mammoscintigraphy has a proven clinical role in the management of breast carcinoma, both for primary diagnosis and for follow-up during chemotherapy,” he said at Seeking Excellence in Breast Cancer Care, a conference sponsored by Johns Hopkins University. “Sentinel node radiolocalization is becoming the procedure of choice for axillary status evaluation. Both procedures are, I think, here to stay, as you say in the United States,” Dr. Maini continued.

Mammoscintigraphy is becoming more widely used because of various drawbacks of screening mammography, Dr. Maini said. Mammography, whose sensitivity is high, has resulted in earlier diagnosis and as much as a 30% reduction in the relative risk of dying from breast cancer for women over age 50. However, interpretation can be difficult in women with dense or dysplastic breasts, fibroadenomas with diffusely distributed calcifications, implants, or other complicating conditions. “The result,” he said, “is many unnecessary biopsies of benign lesions.”

Alternatives include MRI, which has low specificity and high cost, and biopsy, which is high cost, invasive, and leads to disruption of breast architecture. “There is a need for a low-cost technique for women with a low to intermediate risk of breast cancer, and that is mammoscin-tigraphy, preferably with 99m-Tc-MIBI (Miraluma) as the tracer agent,” Dr. Maini said. Pooled data for more than 2,000 patients have demonstrated that mammoscintigraphy has a sensitivity of 85% with specificity of 89%. “Our experience in Rome confirms this,” he added.

Dr. Maini’s institution analyzed more than 300 patients with breast masses who underwent mammoscintigraphy with 99m-Tc-MIBI. In this group, sensitivity was 95% and specificity 79% for lesions of more than 1 cm; for lesions of 1 cm or smaller, sensitivity and specificity were 48% and 100%, respectively. Sensitivity was significantly higher in women under 45 years of age, while specificity was better in women over age 45.

There were 14 false-positive findings and 24 false-negative reports in the group. The false positives were actually highly mitotic juvenile adenomas or other benign conditions, including papillomas and local inflammation. Dr. Maini referred to the false-negative rate as “a troublesome aspect” of mammoscintigraphy.

In the Rome study, 15 of the 24 patients with false-negative reports had lesions of 1 cm or less. Six were tubular carcinomas. “Thus,” Dr. Maini said, “tumor size and differentiation can account for some false negatives, but the reasons for the remaining cases are unclear.”

Mammoscintigraphy also has potential for predicting multidrug resistance noninvasively because it can evaluate the expression of P-glycoprotein (Pgp), Dr. Maini said. Activity of this protein results in decreased cellular drug concentration and cytotoxicity. In an analysis at Dr. Maini’s institution, prechemotherapy mammoscintigraphy correctly identified seven of seven patients who would not respond to chemotherapy because of multidrug resistance.

New camera designs for use in mammoscintigraphy are in the works, including one at Dr. Maini’s institution that has performed well so far. Although they are expensive, Dr. Maini predicted that cameras will become cheaper—and possibly cheaper than the standard cameras now in use.

Like mammography, current techniques for analysis of lymph node status also have their drawbacks. Up to 80% of patients who undergo axillary surgical dissection will have benign conditions, and axillary dissection carries a significant risk of complications. Still, level I and II dissections have become standard practice in the initial staging of early breast cancer, he noted.

“Sentinel node radiolocalization with a hand-held gamma probe is a viable alternative,” Dr. Maini said. The procedure is much less invasive than standard dissection and can be performed on an outpatient basis.

“In experienced hands, the false-negative rate of radiolocalization is well below 5%,” Dr. Maini said. “The skip metastases rate can be estimated as low as 2% or less, if careful patient selection is implemented.” Ineligible patients would include those with multifocal cancers, previous breast surgery or radiotherapy, and possibly those with internal quadrant cancers.