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 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 study was published online on May 11, 2015 by the Journal of Clinical Oncology. Read the abstract of “Identification of a Low-Risk Luminal A Breast Cancer Cohort That May Not Benefit From Breast Radiotherapy.”
Luminal A breast cancer is cancer that is estrogen-receptor positive and/or progesterone-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 samples analyses from 501 women diagnosed with early-stage breast cancer. All the women were participants in an earlier study. The earlier 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. At 10 years, 84% of the women were still alive.
In this study, the researchers measured levels of six biomarkers in the cancer tissue samples for two reasons:
- to classify the cancers into subtypes
- to see if they could help estimate the cancer’s risk of recurrence
Biomarkers are proteins linked to a specific disease. In most cases, the higher the levels of the proteins, the more likely the disease is to develop or recur. The six biomarkers measured were:
- estrogen receptor
- progesterone receptor
- human epidermal growth factor receptor 2 (HER2)
- cytokeratin 5/6
- epidermal growth factor receptor (EGFR)
The researchers classified the breast cancers as one of three subtypes:
- luminal A: estrogen-receptor positive and/or progesterone-receptor positive, HER2-negative, and low levels of Ki-67 -- 265 cancers
- luminal B: estrogen-receptor positive and/or progesterone-receptor positive and either HER2-positive or HER2-negative with high levels of Ki-67 -- 165 cancers
- high-risk subtype: hormone-receptor-negative and HER2-positive disease or triple-negative disease -- 72 cancers
The researchers found that the 10-year risk of recurrence in the same breast for the cancers by subtype was:
- 5.2% for luminal A cancers
- 10.5% for luminal B cancers
- 21.3% for high-risk subtype cancers
When they compared recurrence rates for cancers treated with tamoxifen and radiation therapy versus cancers treated with tamoxifen alone, the researchers found that the luminal A and luminal B subtypes didn’t benefit as much from radiation therapy as the high-risk subtypes. Still, these differences weren’t statistically significant, which means they could have been due to chance and not because of the radiation therapy.
But when the researchers looked at women older than 60 who were diagnosed with subtype luminal A breast cancer, they found that the 10-year risk of recurrence in the same breast was:
- 1.3% for cancers treated only with tamoxifen
- 5.0% for cancers treated with tamoxifen and radiation therapy
This suggests that some women older than 60 diagnosed with luminal A disease -- hormone-receptor-positive, HER2-negative breast cancer with low levels of Ki-67 -- who are taking hormonal therapy after surgery may be able to skip radiation therapy.
While the results of this study are very encouraging, more research is needed before doctors can say for certain if some older women diagnosed with luminal A breast cancer can avoid radiation therapy.
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%.
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, HER2 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 older than 60 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.