Postmastectomy Radiation Therapy (PMRT)
Radiation therapy has been used over the years as a supplemental treatment after surgery to remove (or, in medical terminology, resect) tumors from the body. The main purpose of this use of radiation therapy is to kill any residual cancer cells at the site of the tumor and to improve a patient’s long-term chances of survival. Radiation therapy after lumpectomy (the surgical removal of a malignant tumor and some surrounding normal tissue while preserving the rest of the breast) has been the trend for all invasive breast cancer in patients younger than 70 years of age.
The use of radiation therapy after mastectomy (PMRT) has been limited to those patients who are at significant risk of cancer recurring in the chest wall or in the nodal basins (axilla, supraclavicular area, or internal mammary chain). Doctors generally agree that patients with 4 or more positive axillary nodes, skin involvement or chest wall involvement have a significantly higher risk for the cancer to recur locally at the surgical site or regionally in the nodal basin. Because of this, PMRT is currently standard of care for all patients with locally advanced breast cancers (known as stage III breast cancers) (Ref. 1-3).
As with any treatment, a surgeon will weigh the benefits rendered by that treatment with the risks associated with it. Because of concerns about the side effects of radiation therapy, particularly in patients who have undergone reconstruction with implants, PMRT is selectively used in patients with stage II disease and rarely used in those with stage I disease.
Regarding stage II patients, there is an ongoing debate about how useful PMRT can be for patients with 1-3 positive nodes. European and Canadian studies performed in the 1980s showed a significant decrease in local and nodal cancer recurrence, and better survival for patients who received PMRT (Ref. 4,5). These studies indicated significantly higher rates of cancer recurrences in patients who did not receive PMRT, reaching up to 27%. More recent studies conducted in the United States, however, have found that with the use of modern chemotherapy and appropriate surgical intervention, the cancer recurrence rates without radiation therapy after mastectomy in patients with 1-3 positive nodes were much lower than those in the older European and Canadian trials. The modern series of studies show the rate of recurrences in patients who underwent a mastectomy for tumors less than 5 cm in size and who had 1-3 lymph nodes involved with cancer and did NOT receive PMRT was on the order of 4%-5% (Ref. 6-7). The lower rate of local recurrences in the modern American studies has been attributed to better chemotherapy and perhaps more complete axillary node dissection.
The factors associated with a higher risk of cancer recurrence were noticed in women younger than 50 years of age and in patients with high-grade (more advanced) tumors, particularly those associated with the spread of cancer to the blood vessels and/or lymphatic system (known as lymphovascular invasion). Current guidelines from the National Comprehensive Cancer Network strongly recommend consideration of PMRT in patients with 1-3 positive nodes.
Another ongoing debate is over how useful PMRT can be in patients with positive margins after mastectomy. The current literature does not show evidence to support the routine use of PMRT in these cases. For these patients, PMRT is used on an individualized, case-by-case basis.
In summary, PMRT is standard in patients with stage III breast cancer, selectively used in patients with stage II breast cancer with 1-3 positive nodes, and rarely used in patients with stage I breast cancer.
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Eifel P, Axelson JA, Costa J, et al. National Institutes of Health Consensus Development Conference Statement: adjuvant therapy for breast cancer, November 1-3, 2000. J Natl Cancer Inst. 2001;93:979-989.
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McBride A, Allen P, Woodward W, et al. Locoregional recurrence risk for patients with T1,2 breast cancer with 1-3 positive lymph nodes treated with mastectomy and systemic treatment. Int J Radiat Oncol Biol Phys. 2014;89:392-398.