RT Boost Lowers Recurrence Rate After Breast Conservation

BOSTON—A 16-Gy radiation boost can cut the local recurrence rate by more than half at 5 years for younger breast cancer patients receiving lumpectomy with radiation therapy, according to European Organization for Research and Treatment of Cancer (EORTC) clinical trial results presented at the American Society for Therapeutic Radiology and Oncology meeting.

Harry Bartelink, MD, PhD, professor of radiotherapy, Netherlands Cancer Institute, Antoni van Leeuwenhoek Hospital, Amsterdam, reported that the boost reduced local recurrence rates by 54% in women under age 40 and by 48% in women aged 41 to 50. While younger patients benefited more than older patients, the oldest patients had a drop of 32%. Overall, the recurrence rate was cut by 41%.

These results were so striking at a median follow-up of 5.1 years that Dr. Bartelink reported them to ASTRO midway through the 10-year study of 5,569 women. “They had to change their standard of practice. This is the largest study ever done. It will not be repeated within the next 10 years,” he told ONI.

Jay R. Harris, MD, of the Dana-Farber Cancer Institute, called the study a “blockbuster.” He told the ASTRO audience, “This trial demonstrates that the boost works.” Dr. Harris said the full impact on survival would not be known until the study passes 10 years, but that he never thought the results seen so far could be achieved with minimum cosmetic effects.

Eleven European countries participated in the trial, with 32 radiation therapy departments reporting cases. Strict quality assurance procedures were implemented to ensure that all patients received the same standard of care whether they enrolled at a large teaching hospital or a smaller center in their home community.

The patients all had stage I or II breast cancer, and no tumors were greater than 5 cm in diameter. The average age of the participants was 55 years old, with 1,334 women between the ages of 41 and 50, and 449 aged 40 or under; 60% of the women were postmenopausal, 11% received chemotherapy, and 18% received tamoxifen (Nolvadex).

All the women underwent tumorec-tomy followed by whole breast irradiation of 50 Gy. The vast majority—5,318 patients—had a microscopically complete excision and were randomized to receive no boost or the 16-Gy boost. The remaining 251 patients had incomplete excisions and were randomized between boost doses of 10 Gy and 26 Gy.

Among those who had a complete excision, local recurrences were reported for 182 women in the no-boost group vs 109 patients who received the 16-Gy boost. This results in 5-year actuarial recurrence rates of 6.8% and 4.3%, respectively.

“Age was the most important single factor for local control,” Dr. Bartelink said, adding that the researchers are currently studying the women’s DNA to try to find out why breast cancer is more aggressive in the younger women. “The key appears to be that you have to be more aggressive in treating breast cancer in these women,” he said.

Cosmetic Results

A panel assessed the cosmetic results at 3 years, rating them as excellent/good in 86% of the no-boost group and 71% of the women who received the boost. “Of course, the boost has an impact on cosmetic outcome,” Dr. Bartelink said, “but it must be weighed against the medical benefit afforded by the boost. There is a large positive impact on local control and only a small negative impact on cosmetic outcome.”

The researchers plan to do an analysis of local control and survival at 10 years, he added. They do not see a difference in survival at this point. Nine of 10 participants (91%) were alive 5 years after treatment.