There also has been recent interest in treating with focal radiation only the part of the breast containing the primary tumor. This raises the question of how much the standard whole-breast radiation is reducing the risk of recurrence in other parts of the breast. Freedman and his colleagues looked at the overall risk of recurrence after breast-conserving surgery and whole-breast radiation. They also subdivided these into recurrences near the original primary tumor and elsewhere in the treated breast.
By 15 years after treatment, the risk of true local recurrences was 9%. The risk of recurrence in other parts of the breast within 10 years was very low, as had been suggested by prior studies, but by 15 years it was nearly equal to the risk of recurrence in the original breast quadrant.
"While this may seem to support a favorable outcome for replacing whole-breast irradiation with partial-breast irradiation, our study shows a dramatic shift in the location of recurrence between 10 and 15 years after treatment," said Gary M. Freedman, M.D., lead author of the study.
The researchers compared the risk of recurrence elsewhere in the treated breast to the risk of cancer developing in the unaffected, untreated other breast. They found that for most patients, 7 percent of women had recurrences in other parts of the treated breast compared with 14 percent of women whose cancer recurred in the unaffected, untreated breast 15 years after treatment.
"The rate of recurrence in initially unaffected parts of the breast receiving whole-breast irradiation was half that of the other breast," said Freedman. "This suggests that whole-breast irradiation may have a protective effect."
The study found that the lowest risk of recurrence in other parts of the breast, and in the unaffected, unirradiated breast, was associated with the use of tamoxifen in addition to radiation.
Dr. Freedman concluded, "Very long-term follow-up, at least 10 to 15 years, will be needed for any proposed study of partial breast irradiation to show that the risk of recurrence is not significantly different from recurrence after whole-breast irradiation." Other study authors include Alexandra L. Hanlon, Ph.D., and Penny R. Anderson, M.D., of Fox Chase Cancer Center's radiation oncology department.
Fox Chase Cancer Center, one of the nation's first comprehensive cancer centers designated by the National Cancer Institute in 1974, conducts basic, clinical, population and translational research; programs of prevention, detection and treatment of cancer; and community outreach. For more information about Fox Chase activities, visit the Center's web site at www.fccc.edu or call 1-888-FOX CHASE.