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Radiation Boost to Tumour Bed Improves Breast Cancer Outcomes: Presented at ASTRO

By Ed Susman

LOS ANGELES, CA -- October 31, 2007 -- Adding a boost of radiation to the tumour bed of women undergoing breast cancer conservation surgery improves outcomes -- especially for cases of high-grade cancer or cancer near or at the surgical margins, according to research presented October 29, 2007 at a plenary talk to the 49th annual meeting of the American Society for Therapeutic Radiation and Oncology (ASTRO).

In the Boost-No Boost study performed by doctors working under a protocol of the European Organisation for Research and Treatment of Cancer, doctors determined that the risk of recurrence in breast cancer is reduced when the standard 50 Gray dose of radiation to the whole breast is supplemented with a 16 Gray dose to the excised tumour bed.

An analysis of that study revealed that patients who gained the greatest benefit from the boost as women with high-grade ductal carcinoma in situ or high-grade invasive tumours, said Heather Jones, MD, Assistant Professor of Radiation Oncology at the University of Pittsburgh, Natrona Heights, Pennsylvania, United States.

The researchers also found that the boost reduces risk of recurrence in cases in which cancer cells extend into surgical margins. Having a high-grade invasive tumour or having high-grade ductal carcinoma in situ (DCIS) in the margins of the excised tumour both increases the risk of later relapse, said Dr. Jones said

The original Boost-No Boost study, published earlier this year in the Journal of Clinical Oncology, showed that the risk of relapse was 7% after 10 years if women got the extra dose, compared to 12% without the boost.

To determine which women benefited most from the extra dose, the researchers analysed tissue from a third of the 5,318 women in the larger randomised trial, said Dr. Jones, who became involved in the study during a fellowship at the Netherlands Cancer Institute in Amsterdam, Netherlands.

The study found that if the margin of the tumour was involved, the 10-year risk of relapse was 4% for women who got the boost, compared to 13% for those who did not, a difference that was significant at P =.0001. On the other hand, if the margin was not involved there was no significant difference in the risk of relapse, Dr. Jones said.

If the excised tumour proved to be high-grade invasive, the 10-year risk of relapse was 7% for those who were boosted and 19% for those who weren't, which was significant at P =.002.
If the margin included DCIS, the relapse risk was 5% for boosted women and 17% for unboosted, which was significant at P <.0001.

As well, women 40 or younger who were boosted had the largest absolute risk reduction -- 23.9% versus 13.5% -- which was significant at P =.0014, Dr. Jones said.

"The boost dose reduces the effect of margin involvement and it substantially reduces the risk of local recurrence in our high-risk patients," she concluded.

The Netherlands Cancer Institute has changed its clinical practice to include an extra 16 Gray of radiation aimed at the tumour bed in the wake of the trial, said Harry Bartelink, MD, PhD, Professor of Radiation Oncology at the University of Amsterdam and lead author of the study.

[Presentation title: The Impact of Boost Dose and Margins on the Local Recurrence Rate in Breast Conserving Therapy: Results from the EORTC Boost- No Boost Trial. Plenary 4]

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