Breast-Specific Gamma Imaging Detects Occult Cancer

Nick Mulcahy

July 16, 2010

July 16, 2010 — Breast-specific gamma imaging (BSGI) appears to be comparable to magnetic resonance imaging (MRI) in its ability to detect additional occult breast cancer lesions in women who already have biopsy-proven breast cancer, a new study concludes.

The study involved 159 women. BSGI, which is also known as molecular breast imaging, found occult cancer in the same breast as the index lesion in 9 women (6%) and in the contralateral breast in 5 women (3%).

"Our study demonstrates that the detection of occult foci of breast cancer with BSGI is comparable to that reported for MRI," write the authors, led by Rachel Brem, MD, from the George Washington University Hospital in Washington, DC.

The study appears in the June issue of the Academic Radiology.

The authors say that BSGI, which requires that patients receive a radiotracer injection to image physiologic changes potentially related to breast cancer, has a number of advantages over MRI.

BSGI is more comfortable than MRI (patients are seated during imaging) and allows for "more rapid physician interpretation" because the technology generates 4 to 10 images "compared with hundreds or more for breast MRI," they write.

A radiology expert not involved with the study agreed with the authors about their comparison of BSGI and MRI.

"Patients hate MRIs," said Kathryn Evers, MD, from Fox Chase Cancer Center in Philadelphia, Pennsylvania, adding that patient comfort is greatly improved with BSGI. "It is also much easier to interpret," she said about BSGI.

Nevertheless, Dr. Evers is currently not lobbying her administrators to purchase a BSGI camera for her department of diagnostic imaging.

This technology has a fairly high radiation dose.

"This technology has a fairly high radiation dose for a diagnostic test," she told Medscape Medical News.

"If an imaging technology does not have a low radiation dose, then you have to be more cautious about using it for screening and for follow-up of a benign lesion," Dr. Evers added.

"If they can get the radiation dose down, I'm a fan and I'd buy one in an instant," she said.

No Standard of Care

Currently, there is no standard of care on the use of imaging to see if additional occult breast cancer is present in the same breast as an index lesion or in the contralateral breast, said Dr. Evers.

She noted that neither the National Comprehensive Cancer Network nor the American Society of Clinical Oncology have fully codified "staging MRI" in their breast cancer guidelines.

There is ongoing debate about the use of staging MRI, and weighing benefits and risks is complex, Dr. Evers observed. "Nobody has a good answer."

The contralateral breast findings are more compelling to me.

Nevertheless, Dr. Evers thinks that a stronger argument can be made for imaging the contralateral breast than the breast with the index lesion because many women will receive whole-breast radiation as part of treatment.

"The contralateral breast findings are more compelling to me," she said about both MRI and BSGI, which have similar rates of finding an additional cancer in the opposite breast in women with breast cancer. "Three percent is very small number but a real number," she said about the rate of detection.

Radiation Dose Details

Study author Dr. Brem deferred questions about radiation to the manufacturer of the BSGI machine used in the study — Dilon Diagnostics (Newport News, Virginia) — but pointed out that there is a history of using the radiotracer technetium (99mTc) sestamibi in heart imaging.

"I can tell you that this dose of 99mTc sestamibi has been used for cardiac imaging for over 25 years. Furthermore, we minimize the dose as much as possible," she said.

The radiation dose used in the study was 20 millicuries (mCi), said Doug Kieper, vice president of science and technology at Dilon Diagnostics.

The 20 mCi dose is not a significant concern.

"The 20 mCi dose is not a significant concern for diagnostic breast cancer patients," he told Medscape Medical News.

However, the company is currently conducting a trial to evaluate lower doses of the radiotracer in breast cancer patients, Mr. Kieper said.

He also explained that the dose was in keeping with the dose range approved by the US Food and Drug Administration (FDA) for the use of 99mTc sestamibi in nuclear medicine, but that this approval was for use in the "old generation" of gamma cameras.

"In theory, we can reduce the dose to 8 to 10 mCi, based on the design of the new gamma cameras," Mr. Kieper added, pointing out that the current study was performed with a new-generation camera. However, the study used the higher dose, he said, because a lower non-FDA-approved dose would have required the study team to perform a risk analysis to meet a typical Investigational Review Board's requirements.

Although the study authors did not provide any information in the published study about the radiotracer dose used, Dr. Brem sees the importance of BSGI increasing.

"I believe that BSGI will be adopted at many centers. It is important to realize that MRI and BSGI are not mutually exclusive imaging modalities," she said.

"Many women cannot have MRI because of limitations such as pacemakers, weight [restrictions], or claustrophobia. Therefore, this expands our ability to diagnose breast cancer," she added.

Complementary to Mammography?

BSGI is seen as a potential complementary tool to mammography in screening women for breast cancer because it performs well in women with dense breasts, as previously reported by Medscape Medical News.

However, in this setting, there are well-founded concerns about radiation dose because of the possible radiation risks associated with repeat screening, explained Mr. Kieper.

"In order for this modality to be used in annual screening in an asymptomatic population at standard risk for breast cancer, lower doses should be considered because of lifetime accumulative radiation dose," he said.

Study Findings

The new study was a retrospective review of the records of all patients who underwent BSGI at George Washington Hospital from January 1, 2004 to June 4, 2007.

Among these patients, 159 women were included in the study, having met the following criteria: 1 suspicious breast lesion on physical exam and/or mammography; BSGI performed to look for occult cancerous lesions in the breasts; and 1 or more foci of breast cancer proven by pathology.

Each patient received an injection of 20 to 37 mCi 99mTc sestamibi in an antecubital vein. Immediately after the injection of the radiotracer, imaging began.

The acquisition time for each image was approximately 6 to 10 minutes, with a total imaging time of approximately 40 minutes per study, the authors report.

BSGI detected 14 sites of nonpalpable mammographically occult cancer in the ipsilateral or contralateral breast in 14 of 159 women (9%); in 9 of the 14 women (6%), the occult cancer was in the same breast as the index lesion, and 4 of the 9 women were found to have ductal carcinoma in situ (DCIS).

Five of 159 women (3%) were found to have occult cancer in the contralateral breast, including 1 with DCIS.

Of the 9 ipsilateral cancers, 6 (67%) were in the same quadrant as the index lesion and 3 (33%) were in different quadrants.

The occult infiltrating cancers detected ranged in size from 0.15 cm to 3.60 cm (mean, 1.16 cm). With regard to the tumor grades in the occult cancers, 2 (14.2%) were low grade, 4 (28.5%) were intermediate grade, and 6 (42.8%) were high grade. The grade was unknown for 2 (14.2%).

The researchers have disclosed no relevant financial relationships.

Acad Radiol. 2010;17:735-743. Abstract


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