Full Dose of Radiation Therapy May Not Be Needed for Some Early-Stage Breast Cancers

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In most cases, the standard treatment for early-stage breast cancer is lumpectomy to remove the cancer followed by about 6 weeks of radiation therapy (5 days a week) to destroy any cancer cells that may have been left behind. This two-step approach reduces the risk of breast cancer recurrence (the cancer coming back).

Doctors have wondered if women diagnosed with early-stage disease with a low risk of recurrence needed radiation treatment to the whole breast, which is the current standard of care. Or could these early-stage cancers with a low risk of recurrence be treated with radiation just to the area around where the cancer used to be?

"This is one of the key questions being studied in the area of radiation therapy for early-stage breast cancer," said Marisa Weiss, M.D., Breastcancer.org chief medical officer and director of radiation oncology at Lankenau Medical Center. "Is less equal to or more beneficial than the standard of care?"

Early results from a study suggest that treating just the area around where the cancer used to be with radiation may be as good as treating the whole breast with radiation.

The study was presented on March 9, 2016 at the 2016 European Breast Cancer Conference. Read the abstract of “Partial breast radiotherapy for women with early breast cancer: First results of local recurrence data for IMPORT LOW (CRUK/06/003).”

In the study, called the IMPORT LOW trial, 2,018 women older than 50 who had been diagnosed with early-stage breast cancer and had lumpectomy to remove the cancer were randomly assigned to one of three radiation regimens after surgery:

  • 675 women had the standard full dose of 40 Gy of radiation to the whole breast
  • 674 women had 40 Gy of radiation to the tumor bed and 36 Gy to the rest of the breast
  • 669 women had 40 Gy to the tumor bed only

A Gray, abbreviated Gy, is the way radiation oncologists measure the dose of radiation therapy.

"We considered it important to set up a trial to answer the question: is full dose radiotherapy to the whole breast needed in patients with low-risk early breast cancer?" said Charlotte Coles, M.D., consultant clinical oncologist at Cambridge University Hospitals. "One group of women received standard full dose radiotherapy to the whole breast. A second group received standard full dose to breast tissue closest to where the lump appears and a slightly lower dose further away. A third group received standard full dose radiotherapy to breast tissue closest to where the lump appears but no radiotherapy dose apart from this."

After 5 years of follow-up, local recurrence rates (breast cancer coming back in the same breast) were:

  • 1.1% for women who got the standard dose of radiation
  • 0.2% for women who got the full dose of radiation to the area where the cancer was and a slightly lower dose further away
  • 0.5% for women who got the standard full dose of radiation to the area where the cancer was only

"We found after 5 years that rates of local relapse (the reappearance of a cancer after treatment in the breast where it was originally detected) were very low in all treatment groups, including those receiving less radiotherapy. Moderate and marked changes in normal breast tissue were also low across all groups," Dr. Coles said. "However, we intend to continue to follow up the trial patients for at least 10 years because we know that cancer recurrence can still occur more than 5 years after completion of treatment. It may be that no dose outside the tumor bed is sufficient for many patients, but some dose at a lower level than that given to the tumor bed is more appropriate for others."

"This is a good preliminary look at an important question for which randomized data between whole and partial breast radiation is just emerging," said Dr. Weiss. "We need longer follow-up to really know how these two treatment regimens compare. We also need other trials to report their results."

While these results are very promising, they are still early results. Doctors need longer follow-up information to see whether radiation to just the area where the cancer was offers the same local recurrence rates 7, 9, or 10 years after treatment. Low-risk cancers are slow-growing by nature, so can come back many years after treatment. This is especially important for women who are diagnosed at a relatively younger age and have many years of life ahead of them.

For more information, visit the Breastcancer.org Radiation Therapy section.



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