Mammotomy May Reduce Biopsy Sampling Errors

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

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

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

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

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

The technique also was better able to obtain calcifications. Core needlebiopsy was not able to retrieve 17% of calcifications, while mammotomyfailed in only 4% of cases.

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

"In composite, we take out about 10 times as much tissue with theMammo-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 biopsyprocedure, captures tissue in a sampling chamber. The internal hollow probemoves forward over tissue in the chamber; a rotating blade slices off sectionsof the tissue at the same time that a vacuum device draws the tissue sectionsdown the length of the sampling chamber.

When all tissue has been withdrawn from the chamber, the blade and theelectromechanical vacuum stop, the internal probe containing the tissueis pulled from the breast, the tissue sample is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

The core needle biopsy, in contrast, requires separate needle entriesto sample tissue within and adjacent to an area of abnormality (Figure2). "With core needles, we take some random samples, and we knowwhat is happening in each of them. But if you liken this to a series ofsnapshots, 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 varythroughout the country, mammotomy costs about $1,200 per procedure on average,compared with $1,000 for a core needle biopsy. "However, that $1,200is only 40% of the cost of a surgical biopsy," Dr. Jackman said, "andwe have something that is not only less costly but also less invasive."And for a $200 differential in cost, mammotomy provides much greater accuracythan core needle biopsy, he added.

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