Developed as a way to sample mammographic abnormalities in a potentially less invasive way, stereotactic technology has generated significant controversy. Speaking at the 11th International Breast Cancer Meeting in San Antonio earlier this year, Monica Morrow, MD, of Northwestern University Medical School said that some overly-enthusiastic radiologists consider stereotactic biopsy to be the technique of choice for almost all mammographic abnormalities, whereas some totally disinterested surgeons believe there is no real role for this technique. Dr. Morrow believes that the appropriate position lies somewhere between these two extremes--"stereotactic biopsy is an appropriate technique for a selected group of mammographic abnormalities."
The purported advantages of stereotactic biopsy include:
It can be performed rapidly
It is relatively painless
It avoids scarring, both externally (preserving the cosmetic appearance of the breast), and internally (minimizing distortion at biopsy sites on a mammogram).
Some maintain it is significantly less costly, but this may not be completely accurate, Dr. Morrow said. In the larger context of the treatment of breast cancer, some of the apparent cost savings are lost, especially in cases where the stereotactic biopsy represents an additional step.
Opponents of stereotactic biopsy say that it is often not useful for treatment planning due to insufficient specimens, and false-negative/false-positive results.
The Beginnings: Fine Needle Aspiration
Fine-needle aspiration cytology was the initial stereotactic technique available. In the literature, typical results of this procedure yielded a sensitivity of 91%. Unfortunately, for a variety of reasons, not the least of which is a lack of trained cytopathologists, the use of aspiration cytology never became widespread. One problem is the fact that aspiration cytology can identify a mammographic abnormality as benign, but can't specify the type of lesion. Furthermore, this procedure does not reliably distinguish invasive from in situ carcinoma, a major difficulty in planning treatment. Finally, any atypia on cytology requires biopsy, although only approximately 20% will actually be cancer.
Core Needle Breakthrough
With the development of core needles that fit into the stereotactic biopsy holder, the technique became much more appealing, Dr. Morrow said. As opposed to collecting a cytologic specimen, a core of tissue for histopathologic examination was obtained. The results of a core biopsy (confirmed by open surgical biopsy) generally indicate a sensitivity in the upper 90% range.
One of the technical factors affecting the outcome of a core biopsy is needle size, with larger needles (commonly 14 gauge) providing better results. The number of specimens taken also influences the results. Many investigators are obtaining 10 cores as a sampling procedure. To confirm the presence of calcification when this is the indication for biopsy, the core specimen should undergo x-ray. Also, whether or not lobular carcinoma in situ is classified as a malignancy will influence sensitivity.
Proponents of stereotactic core biopsy claim that it renders a definitive diagnosis of benign abnormalities, eliminates the false-positive results seen with cytology due to atypia, distinguishes invasive from in situ carcinoma, and enables surgeons to perform a definitive operation armed with a diagnosis of cancer. However, many of these claims are debatable, Dr. Morrow said.
A review of the literature indicates that a core biopsy correctly diagnosed ductal carcinoma in situ in only 70% of cases. (All of the core biopsies were confirmed surgically.) Based on this limited information, it appears that a core biopsy's ability to reliably identify ductal carcinoma in situ may be considerably less than that reported for invasive carcinoma.
Furthermore, the information obtained from a core biopsy does not necessarily correlate with intraoperative findings. Although ductal carcinoma in situ was detected using optimal core technique (a mean number of core samplings of seven per case with a large-gauge needle) in a study of 82 cases of cancer, 10% of the time invasive cancer that was not found by the biopsy core was identified on open biopsy. In another 6% of cases, when simple invasive cancer was identified on the biopsy core, an extensive intraductal component was found intraoperatively. In essence, there have been some difficulties with the pathologic information obtained from the core biopsy and the ability to sample certain breast lesions.
Although one of the apparent advantages of a core biopsy is the avoidance of sampling the atypias seen with cytology, many of the atypical hyperplasias found on core biopsies actually were found to be cancer on open biopsy.
The claim that being armed with a diagnosis of cancer somehow helps a surgeon perform a lumpectomy more effectively has not been substantiated, according to Dr. Morrow. In a series of 239 lumpectomies, 173 were performed as diagnostic procedures, and 66 were performed with a cancer diagnosis obtained via fine-needle aspiration. The total positive margin rate was 5%. Therefore, regardless of whether or not there was prior knowledge of cancer, conservative lumpectomy as a single operation was effective 95% of the time.
Although many of the alleged benefits of the core biopsy have not been confirmed, it is a useful procedure in certain cases. For example, to avoid open biopsy, Dr. Morrow may use core biopsy for mammographic abnormalities that are suspicious but deemed unlikely to be cancerous--lesions that, on mammography, have perhaps a 2 to 20% risk of being malignant.
In summary, Dr. Morrow recommends stereotactic core needle biopsy be considered for:
Relatively nonsuspicious breast lesions that are not clearly benign.
Women who are candidates for breast-conserving surgery but are found to have other benign-appearing lesions elsewhere in the breast.
Women who are candidates for mastectomy only.
As an alternative for women with significant co-morbidities such that open biopsy would be more hazardous than usual.