August 10, 2007 - A study published this week in the August 11th issue of the journal The Lancet concludes that screening using Breast magnetic resonance imaging (MRI) could help improve the ability to diagnose breast cancer early, while it is still classified as “ductal carcinoma in situ” (DCIS), and prevent its progression to invasive cancer.
In DCIS, aggressive precancerous growths form in the lining of the milk duct and increase the chances that a woman will develop breast cancer by 40 percent. Approximately 17 percent of the 52,000 cases of DCIS diagnosed in the U.S. each year are considered to be “high-grade.” High-grade DCIS is easily removed by surgery if detected early but if untreated can develop into invasive breast cancer.
Several previous studies have documented the superiority of MRI over mammography for detecting DCIS as well as invasive breast cancer, both for screening high risk women and for follow up of women with abnormal mammogram findings or clinical symptoms. In the Lancet study (‘MRI for diagnosis of pure ductal carcinoma in situ: a prospective observational study’) of 167 women who were screened with both mammography and MRI, more DCIS cancers were diagnosed with MRI and these cancers were more likely to be high-grade and thus more likely to progress to invasive cancer.
While the authors conclude that using breast MRI for screening among general populations of women is not appropriate at this time, an accompanying editorial suggests breast MRI should no longer be regarded as an adjunct to mammography, but as a distinct method to detect breast cancer in its earliest stage, and calls for a large-scale trial in the general population. In contrast, the American Cancer Society recommends use of breast MRI in screening of women at high risk for breast cancer, but not among women of average risk because of its rate of false positive results, leading to unnecessary biopsies.
However, a study by a research team at the Seattle Cancer Care Alliance and the University of Washington Medical Center, led by Constance Lehman, M.D., published in July in the peer-reviewed journal Radiology indicates that computer-aided detection (CADstream) technology used with breast MRI reduces the number of false positives and unnecessary biopsies.
About the Lancet Study:
Professor Christiane Kuhl, Department of Radiology, University of Bonn, Germany, and colleagues studied 7319 women over a five-year period who had been referred to an academic breast center because of an abnormal mammogram result, clinical symptoms of breast cancer, being considered at high risk based on genetics or family history, or a previous diagnosis of breast cancer. The women received MRI in addition to conventional mammography for diagnostic assessment and screening, with the aim of discovering the sensitivity of each method for diagnosing DCIS. Mammograms and MRI scans were then assessed independently by different radiologists, and the relative sensitivity of each method of detection was assessed.
The researchers found that of 167 women who had a diagnosis of DCIS, 153 (92%) were diagnosed by MRI compared with 93 (56%) diagnosed by mammography. While the sensitivity of MRI for diagnosing DCIS increased with nuclear grade, that of mammography decreased. Of 89 women diagnosed with “high grade” DCIS, 87 (98%) were diagnosed by MRI, but only 46 (52%) by mammography. Accordingly, almost half (48%) were missed by mammography but diagnosed by MRI alone.
They also found that age, menopausal status, personal or family history of breast cancer, and breast density of women with MRI-only diagnosed disease did not differ significantly from those of women with mammography-diagnosed DCIS. The higher sensitivity of MRI was not associated with an unduly high number of false positive diagnoses; the positive predictive value of both methods was comparable, with 55% for mammography, and 59% for MRI.
The authors concluded, “Our study suggests that the sensitivity of film screen or digital mammography for diagnosing DCIS is limited…MRI could help improve the ability to diagnose DCIS, especially DCIS with high nuclear grade.”
In an accompanying editorial comment, Dr Carla Boetes and Dr Ritse Mann, Radboud University Nijmegen Medical Centre, Netherlands, stated, “These findings can only lead to the conclusion that MRI outperforms mammography in tumour detection and diagnosis. MRI should thus no longer be regarded as an adjunct to mammography but as a distinct method to detect breast cancer in its earliest stage. A large-scale multicentre breast-screening trial with MRI in the general population is essential.”
For more information: www.thelancet.com