Adjuvant Radiation Therapy
Radiation therapy is regularly employed after breast-conservation surgery. Radiation therapy also can be indicated for postmastectomy patients. The main goal of adjuvant radiation therapy is to eradicate residual disease thus reducing local recurrence.
Post-breast conservation surgery
For women who are treated with breast-conserving surgery, the most common site of local recurrence is the conserved breast itself. The risk of recurrence in the conserved breast is substantial (>20%) even in confirmed axillary lymph node-negative women. Thus, whole breast radiation therapy after breast-conserving surgery is recommended.
Although all trials assessing the role of radiation therapy in breast-conserving therapy have shown highly statistically significant reductions in local recurrence rate, no single trial has demonstrated a statistically significant reduction in mortality. However, in the 2005 Early Breast Cancer Trialists’ Collaborative Group’s (EBCTCG) update, when all relevant trials were combined, 15-year breast cancer mortality was reduced from 35.9% to 30.5% in women receiving radiation therapy (absolute difference of 5.4%; 95% CI, 2.1%–8.7%; breast cancer death rate ratio 0.83; 95% CI, 0.75–0.91; P = .002). There was a similar effect on all-cause mortality.
Although adjuvant whole-breast radiation is standard treatment, no trials have addressed the role of regional lymph node radiation therapy in this setting. The National Cancer Institute of Canada’s study (CAN-NCIC-MA20[NCT00005957]) has closed, but until results are reported, decisions regarding the use of such therapy must rely on extrapolations from the postmastectomy setting and on knowledge of the local-regional recurrence rates following conservation therapy with axillary lymph node dissection for a given lesion.
Postoperative chest wall and regional lymph node adjuvant radiation therapy has traditionally been given to selected patients considered at high risk for local-regional failure following mastectomy. Radiation therapy can decrease local-regional recurrence in this group, even among those patients who receive adjuvant chemotherapy. Patients at highest risk for local recurrence include those with four or more positive axillary nodes, grossly evident extracapsular nodal extension, large primary tumors, and very close or positive deep margins of resection of the primary tumor.[63-65]
Patients with one to three involved nodes without any of the previously noted risk factors are at low risk of local recurrence, and the value of routine use of adjuvant radiation therapy in this setting has been unclear. The 2005 EBCTCG update indicates, however, that radiation therapy is beneficial, regardless of the number of lymph nodes involved.[Level of evidence: 1iiA] For women with node-positive disease postmastectomy and axillary clearance, radiation therapy reduced the 5-year local recurrence risk from 23% to 6% (absolute gain = 17%; 95% confidence interval [CI], 15.2%–18.8%). This translated into a significant (P = .002) reduction in breast cancer mortality, 54.7% versus 60.1% with an absolute gain of 5.4% (95% CI, 2.9%–7.9%). In subgroup analyses, the 5-year local recurrence rate was reduced by 12% (95% CI, 8.0%–16%) for women with one to three involved lymph nodes and by 14% (95% CI, 10%–18%) for women with four or more involved lymph nodes. In contrast, for women with node-negative disease, the absolute reduction in 5-year local recurrence was only 4% (P = .002; 95% CI, 1.8%–6.2%), and there was not a statistically significant reduction in 15-year breast cancer mortality in these patients (absolute gain = 1.0%; P > .1 95%; CI, -0.8%–2.8%). Further, an analysis of NSABP trials showed that even in patients with large (>5 cm) primary tumors, when axillary nodes were negative, the risk of isolated locoregional recurrence was low enough (7.1%) that routine locoregional radiation therapy was not warranted.
Late toxic effects of radiation
Late toxic effects of radiation therapy, though uncommon, can include radiation pneumonitis, cardiac events, arm edema, brachial plexopathy, and the risk of second malignancies. Such toxic effects can be minimized with current radiation delivery techniques and with careful delineation of the target volume.
In a retrospective analysis of 1,624 women treated with conservative surgery and adjuvant breast radiation at a single institution, the overall incidence of symptomatic radiation pneumonitis was 1.0% at a median follow-up of 77 months. The incidence of pneumonitis increased to 3.0% with the use of a supraclavicular radiation field and to 8.8% when concurrent chemotherapy was administered. The incidence was only 1.3% in patients who received sequential chemotherapy.[Level of evidence: 3iii]
Controversy existed as to whether adjuvant radiation therapy to the left chest wall or breast, with or without inclusion of the regional lymphatics, had an association with increased cardiac mortality. In women treated with radiation therapy before 1980, an increased cardiac death rate was noted after 10 to 15 years, compared with women with nonradiated or right-side-only radiated breast cancer.[62,68-70] This was probably caused by the radiation received by the left myocardium.
Modern radiation therapy techniques introduced in the 1990s minimized deep radiation to the underlying myocardium when left-sided chest wall or left-breast radiation was used. Cardiac mortality decreased accordingly.[71,72] At this time, cardiac mortality was also decreasing in the United States.
An analysis of SEER data from 1973 to 1989 reviewing deaths caused by ischemic heart disease in women who received breast or chest wall radiation showed that since 1980, no increased death rate resulting from ischemic heart disease in women who received left chest wall or breast radiation was found.[73,74][Level of evidence: 3iB]
Lymphedema consequent to cancer management remains a major quality-of-life concern for breast cancer patients. Single-modality treatment of the axilla (surgery or radiation) is associated with a low incidence of arm edema. Axillary radiation therapy can increase the risk of arm edema in patients who received axillary dissection from 2% to 10% with dissection alone to 13% to 18% with adjuvant radiation therapy.[75-77] (Refer to the PDQ summary on Lymphedema for more information.)
Radiation injury to the brachial plexus following adjuvant nodal radiation therapy is a rare clinical entity for breast cancer patients. In a single-institution study using current radiation techniques, 449 breast cancer patients treated with postoperative radiation therapy to the breast and regional lymphatics were followed for 5.5 years to assess the rate of brachial plexus injury. The diagnosis of such injury was made clinically with computerized tomography to distinguish radiation injury from tumor recurrence. When 54 Gy in 30 fractions was delivered to the regional nodes, the incidence of symptomatic brachial plexus injury was 1.0% compared with 5.9% when increased fraction sizes (45 Gy in 15 fractions) were used.
The rate of second malignancies following adjuvant radiation therapy is very low. Sarcomas in the treated field are rare, with the long-term risk at 0.2% at 10 years. One report suggests an increase in contralateral breast cancer for women younger than 45 years who have received chest wall radiation therapy after mastectomy. No increased risk of contralateral breast cancer occurs for women 45 years and older who receive radiation therapy. Techniques to minimize the radiation dose to the contralateral breast should be used to keep the absolute risk as low as possible. In nonsmokers, the risk of lung cancer as a result of radiation exposure during treatment is minimal when current dosimetry techniques are used. Smokers, however, may have a small increased risk of lung cancer in the ipsilateral lung.