DuPont explores scintimammography after winning FDA nod for Miraluma radiotracer

New product is based on Cardiolite technetium sestamibi heart agent

DuPont Merck Radiopharmaceuticals got a big boost in its quest to expand applications for its technetium sestamibi radiopharmaceutical when the Food and Drug Administration last month approved breast imaging indications for the product. In addition to benefiting Du Pont Merck, the FDA's action should provide a catalyst for nuclear medicine physicians who are exploring scintimammography, one of the most exciting new applications to emerge in nuclear medicine in years.

Du Pont Merck has been marketing technetium sestamibi since 1991 for cardiac perfusion applications under the brand name Cardiolite. The radiotracer has been an unqualified success for the North Billerica, MA, company, and has helped fuel the rapid growth of nuclear cardiology.

Du Pont Merck several years ago began to suspect that Cardiolite might have breast imaging applications, because cancerous tumors are more vascularized than normal tissue and thus have higher concentrations of mitochondria, to which sestamibi binds, according to Robert Williams, brand director of oncology at Du Pont Merck. At the same time, physicians using Cardiolite for heart studies were noticing higher uptake in breast tissue that later turned out to be malignant.

"It was a combination of serendipity and suspicion," Williams said. "While it was somewhat surprising to see this uptake, it was not a total surprise."

Du Pont commissioned a multicenter study in 1995 to investigate Cardiolite's potential as a breast imaging agent and to gather the clinical data required for a submission to the FDA for a supplement to Cardiolite's new drug application (SCAN 8/2/95). The study included 42 institutions in North America, and 672 patients were studied, Williams said.

The results indicated that technetium sestamibi had a positive predictive value of 83% in patients with palpable lesions, and a negative predictive value of 78%. It had a sensitivity of 76% and a specificity of 85% in patients with palpable lesions. For patients with nonpalpable lesions, Miraluma had a positive predictive value of 79% and a negative predictive value of 80%. The tracer had a sensitivity of 52% and a specificity of 94% for patients in this group.

Du Pont executives are careful in how they characterize the way they see Miraluma being used. The product's labeling states that it is indicated for planar imaging as a second-line diagnostic drug after mammography to assist in the evaluation of breast lesions in patients with an abnormal mammogram or a palpable breast mass. Miraluma is not indicated for breast cancer screening, to confirm the presence or absence of malignancy, or as an alternative to biopsy.

The company believes that Miraluma should help provide radiologists with additional information about questionable mammograms, particularly in women with dense breasts, which are often difficult to visualize using conventional x-ray mammography. A Miraluma study can also be useful in studies of women who have breasts that include scar tissue that might obscure lesions on a mammogram.

While scintimammography is a cutting-edge technology, Du Pont Merck believes that the technique may prove most valuable at smaller community hospitals rather than at the luminary sites that are known for innovation. Radiologists at smaller facilities often do not have an armamentarium of imaging technology that can be used to resolve difficult mammograms. Miraluma should help, Williams said.

How big is the potential market for Miraluma? There are about 25 million to 30 million mammograms conducted in the U.S. each year, and about 11% of those patients go on to biopsy. While Miraluma clearly will be used for only a percentage of those cases, the product's potential market remains quite large.

Despite Miraluma's potential, the nuclear medicine market has been less than kind to new radiopharmaceutical introductions in the past few years. For Miraluma to succeed, Du Pont Merck is going to have to conduct an extensive outreach campaign, not just to nuclear medicine physicians but also to the mammographers who will be referring patients for Miraluma exams.

"The interesting thing is that (scintimammography) is not news to nuclear medicine physicians-they have heard about this for several years," Williams said. "But in radiology, it is news. One of the first things we have to do is to show radiologists, especially community radiologists, what this technique is all about."