Adjunctive breast imaging modalities come up short

A noninvasive diagnostic test would be preferred over biopsy to exclude or confirm breast cancer, but no currently available technique fits the bill, according to a study released by the Agency for Healthcare Research and Quality.

Researchers retrospectively reviewed 81 studies that evaluated the accuracy of scintimammography, PET, ultrasound, or MRI to diagnose breast cancer in women.

Results indicate that the four tests would miss from about 4% to 9% of cancer cases among women testing negative who have average risk for the disease, with potentially more missed cancers among women at higher risk.

The researchers concluded that for every 1000 women who had a negative scintimammogram, 93 would have missed cancers. For the same number of women with negative scans, PET would miss 76 cancers, ultrasound 50, and MRI 38.

The numbers of women out of that 1000 who would avoid unnecessary biopsies would be 907, 924, 950, and 962, respectively, for each modality.

The question society has to ask, according to the study, is how accurate does a test have to be before it becomes an acceptable and appropriate alternative to biopsy. An analysis by the Ontario Ministry of Health concluded that a negative predictive value of 98% or greater would be an acceptable level for a diagnostic test to reliably preclude breast biopsy.

A threshold of 98% means that 20 cases of breast cancer would be missed in exchange for avoiding 980 unnecessary biopsies. All of the tests in this evaluation fell short of that threshold.

The American College of Radiology issued a statement calling the report simplistic, misleading, and inaccurate.

"It is well known among breast imagers (radiologists) that additional imaging studies should not be used to obviate the need for biopsy of a suspicious mammographic finding," the statement said.

The ACR further said that the report, Effectiveness of noninvasive diagnostic tests for breast abnormalities, reflects a serious lack of understanding of the steps involved in detecting and diagnosing breast cancer with imaging procedures.

The college expressed concern that women would be misled by the report and might forego additional imaging after an inconclusive screening mammogram or might prematurely demand a biopsy.

The authors of the study wrote that the evidence supporting their conclusions permits them to be moderately confident that publication of future studies will not overturn their findings.

The five-year survival rate of stage 0 breast cancer is 100%, dropping to 16% for stage IV. The earlier breast cancer is diagnosed, the higher the survival rate. Biopsies are often ordered for lesions scored as BI-RADS 4 (suspicious abnormality) or 5 (highly suggestive of malignancy). In an average risk group, however, only 20% of these women will have cancer.

Patients diagnosed with BI-RADS 3 (probably benign) or BI-RADS 0 (uninformative mammography) often undergo repeat mammography. Patients with lesions in all four BI-RADS groups would benefit from an accurate noninvasive diagnostic test, according to the study.

An average woman in the U.S. who has an abnormal mammogram requiring a biopsy for evaluation has about a 20% risk of cancer.

The AHRQ study found that the negative likelihood ratio for scintimammography of women referred for further evaluation was 0.41. This finding means that if a woman with a nonpalpable lesion is diagnosed as cancer-free by scintimammography, her chance of actually having breast cancer drops from 20% to 9.3%.

The chance of actually having breast cancer dropped from 20% in the other modalities to:

• 7.6% for PET, with a negative likelihood ratio of 0.33

• 5% for ultrasound, with a negative likelihood ratio of 0.21

• 3.8% for MRI, with a negative likelihood ratio of 0.16

"So many women today undergo biopsies only to learn they do not have breast cancer. Hopefully, noninvasive tests can continue to improve so that in the future, there will be a viable alternative to biopsy," said AHRQ director Dr. Carolyn M. Clancy. "But early and accurate diagnosis of breast cancer is crucial, and at this time, biopsies remain the most effective technique when mammography or physical examination reveals a potential problem."

For more information from the Diagnostic Imaging archives:

Intervention widens breast disease options

Adjunctive technique improves both sensitivity and specificity

False positives decline with breast tomosynthesis

Radiologists benefit from uptick in breast biopsies