MRI determines cancer spread into breast ducts

MRI can be used to determine if and how far breast cancer has spread into the breast ducts before patients receive breast-conserving therapy, according to results from a Japanese study.

The study included 69 patients with proven invasive cancer, 44 of which had an intraductal component. MRI correctly identified 33 of the 44 cases.

"Accurate preoperative diagnosis of the intraductal component allows the surgeon to achieve a cancer-free surgical margin," said Dr. Akiko Shimauchi, a radiologist at Tohoku University in Sendai, Miyagi, Japan.

Patients have a lower survival rate if their surgical margins are positive for tumor cells, she said. This is usually the result of inadequate resection of the cancer's intraductal component.

CT may also be used to determine whether the cancer has invaded ducts in the breast, but the researchers found that MRI outperformed this modality. CT correctly identified 27 of 44 cases, six fewer than MRI, and MRI had a significantly higher sensitivity (75%) than CT (61%).

"The lesions that were missed by both examinations were the ductal extension type," Shimauchi said. "The tumor included a dominant mass with an outward extension of cancer cells, with a relatively small ductal component."

MRI was better able to detect the smaller ductal components than CT, according to Shimauchi.

But the study also found that both CT and MRI tended to underestimate the length of the intraductal component, although MRI was less prone to such errors. Underestimation by 15 mm or more occurred with MRI in 30% of cases compared to 55% with CT. The way around this shortcoming is to err on the side of caution.

"In our institution, surgeons use a surgical margin that is 20 mm outside the radiologically determined tumor margin," Shimauchi said.