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MRI Detected Breast Cancers Earlier in High-Risk Women


 

Major Finding: In a sample of women with BRCA1 and −2 mutations, 13% of invasive cancers in an MRI surveillance group were node positive, compared with 40% in controls.

Data Source: The nonrandomized study involved 1,275 women with BRCA1 and −2 mutations.

Disclosures: Dr. Warner served as a consultant to Berlex and Bayer.

SAN ANTONIO — Adding MRI surveillance to conventional mammography in women with BRCA1 or BRCA2 mutations results in a favorable stage shift, with breast cancers being detected at an earlier, more curable stage, according to a prospective cohort study.

This finding is consistent with the notion that MRI surveillance reduces distant recurrence rates and breast cancer mortality, although definitive proof must await another 5–10 years of study follow-up, Dr. Ellen Warner reported at the San Antonio Breast Cancer Symposium.

In the meantime, these encouraging interim results will hopefully convince very high-risk women and their physicians that surveillance with yearly MRI and mammography is a reasonable alternative to prophylactic mastectomy, added Dr. Warner of the University of Toronto.

A randomized controlled trial comparing MRI surveillance to mammography will never happen for ethical as well as practical reasons, she asserted.

The next-best study design would be a prospective cohort study, Dr. Warner said.

Such a study is underway in Toronto. It involves 1,275 women with BRCA1 or −2 mutations who to date have been followed for a mean of 3.2 years for incident breast cancer.

The nonrandomized study involves 445 women in a Toronto surveillance program involving annual MRI and mammography along with twice-yearly clinical breast examination and a control group comprising 830 women who were screened by annual mammography and twice-yearly clinical breast examinations.

There have been 41 cases of invasive breast cancer detected in the MRI group and 77 in the controls.

The incidence in the two groups was nearly identical.

However, there was a marked difference in cancer stage. Only 13% of invasive cancers in the MRI group were node positive, compared with 40% in the controls (P = .009).

The mean 9-mm tumor size in the MRI group was one-half that in the controls.

Only 3% of invasive tumors in the MRI group exceeded 20 mm, compared with 29% in the controls.

Ductal carcinoma in situ (DCIS) was detected in 2.2% of the MRI group and 1.1% of the controls.

After baseline differences in menopausal status, tamoxifen therapy, and other potential confounders were controlled for, the MRI cohort was 5.7-fold more likely than the controls to be diagnosed with DCIS, threefold more likely to be diagnosed with stage I breast cancer, and one-quarter as likely to have stage II or higher breast cancer.

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