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Mammotomy May Reduce Biopsy Sampling Errors

Mammotomy May Reduce Biopsy Sampling Errors

CHICAGO--A percutaneous breast biopsy method that uses a thin rotating blade to snip off tissue and a vacuum element to withdraw pathological samples is proving to be three times more accurate and two times faster than core needle biopsy, said Roger J. Jackman, MD, of the Department of Diagnostic Radiology, Palo Alto Medical Clinic, Calif, at the annual meeting of the Radiological Society of North America (RSNA).

Using the Mammotome Breast Biopsy System, manufactured by Biopsys Medical, Inc, Irvine, Calif (see Figure 1 ), radiologists from seven institutions across the country have significantly reduced sampling errors associated with standard core needle biopsy.

Dr. Jackman and his colleagues compared the results of breast biopsies in medical records of 2,093 women who had mammotomy with the results of core needle biopsy data from the literature.

They found that mammotomy drastically decreased the number of cases of malignancies that were misidentified as atypical ductal hyperplasia (ADH). Only 18% of the lesions identified as ADH in mammotomy samples were malignant at surgery, compared with 49% of the lesions classified as ADH in core needle biopsy samples.

Mammotomy nearly cut in half the number of cases of invasive cancer that masqueraded as ductal carcinoma in situ (DCIS). Invasive cancer was missed in 16% of breast biopsies obtained by the core needle technique but in only 9% of mammotomy biopsies.

The technique also was better able to obtain calcifications. Core needle biopsy was not able to retrieve 17% of calcifications, while mammotomy failed in only 4% of cases.

Mammotomy can improve the diagnosis of cancer in nonsurgical breast biopsies because it removes more tissue in less time, Dr. Jackman said. Mammot-omy captures tissue samples that are 2.5 times as large as those obtained with core needles, and it removes twice as many samples per unit of time.

"In composite, we take out about 10 times as much tissue with the Mammo-tome as we do with the core needle," Dr. Jackman said.

The mammotomy system consists of an external and an internal probe. The external probe, which remains inside the breast throughout the biopsy procedure, captures tissue in a sampling chamber. The internal hollow probe moves forward over tissue in the chamber; a rotating blade slices off sections of the tissue at the same time that a vacuum device draws the tissue sections down the length of the sampling chamber.

When all tissue has been withdrawn from the chamber, the blade and the electromechanical vacuum stop, the internal probe containing the tissue is pulled from the breast, the tissue sample is removed from the sampling chamber, and the internal probe is slid back into place so that the external probe can be rotated to a new location within the lesion.

The core needle biopsy, in contrast, requires separate needle entries to sample tissue within and adjacent to an area of abnormality (Figure 2). "With core needles, we take some random samples, and we know what is happening in each of them. But if you liken this to a series of snapshots, we don't know what is in the rest of the landscape," Dr. Jackman said. "With the mammotome approach, we get a panoramic view, so there's much less potential hidden information."

Cost Comparison

Mammotomy is more costly than core needle biopsy. Although charges vary throughout the country, mammotomy costs about $1,200 per procedure on average, compared with $1,000 for a core needle biopsy. "However, that $1,200 is only 40% of the cost of a surgical biopsy," Dr. Jackman said, "and we have something that is not only less costly but also less invasive." And for a $200 differential in cost, mammotomy provides much greater accuracy than core needle biopsy, he added.

Mammotomy was approved by the FDA in 1995. At present, there are only about 300 devices in use in the United States. These devices can be used with standard stereotactic breast biopsy tables and radiologic equipment. The operating element is reusable; the probe, tubing, and canister for collecting blood, etc, are disposable.

 
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