ScienceDaily (Sep. 4, 2006) — MRI is better than MDCT for determining if and how far breast cancer has spread into the breast ducts and should be used before patients receive breast conserving therapy, a new study shows.

"Patients have a lower survival rate if their surgical margins are positive for tumor cells. A positive surgical margin is usually the result of inadequate resection of the cancer's intraductal component," said Akiko Shimauchi, MD, at Tohoku University in Sendai, Miyagi, Japan. "Accurate preoperative diagnosis of the intraductal component allows the surgeon to achieve a cancer-free surgical margin," she said.

The study included 69 patients with proven invasive cancer, 44 of which had an intraductal component, said Dr. Shimauchi. MRI correctly identified 33 of the 44 cases, while MDCT correctly identified 27. "MRI revealed the presence of the intraductal component with significantly higher sensitivity (75%) compared to MDCT (61%), Dr. Shimauchi said.

"The lesions that were missed by both examinations were the ductal extension type, i.e. the tumor included a dominant mass with an outward extension of cancer cells, with a relatively small ductal component," said Dr. Shimauchi. MRI was better able to detect the smaller ductal components than MDCT, she said.

The study also found that both MDCT and MRI "generally underestimated the length of the intraductal component," however, MRI was less likely to underestimate the length of the intraductal component than MDCT. "In our institution, surgeons err on the side of caution by using a surgical margin that is 20 mm outside the radiologically determined tumor margin," said Dr. Shimauchi. Underestimation of the length of the intraductal components by 15 mm or more was significantly less frequent with MRI (30%) compared to MDCT (55%), she said.

The study was published in the August, 2006 American Journal of Roentgenology, the official journal of the American Roentgen Ray Society.

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