Some Older Women Treated With Hormonal Therapy After Surgery May Be Able to Skip Radiation

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For early-stage breast cancer, lumpectomy followed by radiation therapy has been shown to be as effective as mastectomy without radiation for removing the cancer AND minimizing the risk of the cancer coming back (recurrence).

Radiation therapy given after surgery is called adjuvant radiation therapy. Adjuvant radiation therapy can destroy any cancer cells that may have been left behind after surgery, making recurrence in the same breast (local recurrence) less likely. Today, almost all women get radiation therapy after lumpectomy. Depending on the characteristics of the cancer, chemotherapy, hormonal therapy, and targeted therapy medicines also may be given after surgery to reduce the risk of the cancer coming back in the same breast or other places in the body.

A small study suggests that women older than 60 who have surgery to remove a relatively lower-risk type of invasive breast cancer -- luminal A breast cancer -- and who get hormonal therapy after surgery may be able to skip radiation therapy after surgery.

The results were presented at the 2012 Annual Meeting of the American Association of Cancer Research. Read the abstract of the study: Post-menopausal women with luminal A subtype might not require breast radiotherapy: Preliminary results from a randomized clinical trial of tamoxifen + radiation.

Luminal A breast cancer is cancer that is hormone-receptor-positive, HER2-negative, and has low levels of the protein Ki-67, which helps control how fast cancer cells grow.

The researchers used information and tissue sample analyses from 304 women diagnosed with early-stage, hormone-receptor-positive breast cancer who had surgery to remove the cancer who were in an earlier study. The original study compared the risk of breast cancer coming back in the same breast 10 years after diagnosis between the women who got tamoxifen, a type of hormonal therapy, and radiation therapy after surgery and women who got only tamoxifen after surgery.

For this newer analysis, the researchers analyzed links between the breast cancer tissue characteristics and treatment outcomes in:

  • 159 women who got radiation therapy and tamoxifen after surgery
  • 145 women who got tamoxifen but not radiation therapy after surgery

The researchers looked for links between breast cancer characteristics (based on tissue analysis) and the risk of the cancer coming back in the same breast. Compared to women with other types of breast cancer, the 133 women who had luminal A breast cancer (hormone-receptor-positive, HER2-negative, and low Ki-67) had the lowest risk of breast cancer coming back in the same breast.

The researchers also looked at the effect radiation therapy after surgery had on the risk of breast cancer coming back in the same breast. Radiation therapy after surgery lowered the risk of recurrence quite a bit in women with breast cancers other than luminal A. In women with luminal A breast cancer, recurrence was lower in women who got radiation therapy after surgery compared to women who didn't. Still, the difference in recurrence risk was small enough that it could have been due to chance and not because of the different treatments.

In the 103 women age 60 or older with luminal A breast cancer, radiation therapy after surgery didn't reduce the risk of the cancer coming back in the same breast at all:

  • 4.3% of these older women who got only tamoxifen after surgery had a local recurrence compared to 6% of women who got both radiation therapy and tamoxifen after surgery

Classifying breast cancer as luminal A requires testing for the Ki-67 protein. A staining process measures the percentage of tumor cells that are positive for Ki-67. The more positive cells there are, the more quickly they are dividing and forming new cells. In breast cancer, a result of less than 10% is considered low, 10-20% borderline, and more than 20% is considered high. For this study, breast cancer was classified as luminal A if the cancer was hormone-receptor-positive, HER2-negative, had a Ki-67 result of less than 14%.

This study was small and based on information from an older study that wasn't designed to look for links between cancer type and the benefits of radiation therapy after surgery. While Ki-67 testing is often done today, it's not done consistently and test results aren't always reliable. Still, if Ki-67 testing is done with other standard tests (hormone receptor status, HER-2 status), it could allow doctors to better classify cancer tissue type and help make treatment decisions.

If you've been diagnosed with early-stage breast cancer and are planning treatment with your doctor, you might want to ask if Ki-67 testing was done on the cancer tissue and how the results might influence treatment decisions. Based on this study, Ki-67 testing might make even more sense if you're 60 or older and radiation therapy after surgery is being considered as part of your treatment plan.

In the Breastcancer.org Symptoms and Diagnosis section, you can learn much more about the ways breast cancer tissue is analyzed, why tests are done and what the results mean, and get help making sense of your pathology report.

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