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Postmastectomy Radiation: Then and Now

Postmastectomy Radiation: Then and Now

Dr. Fowble's well-written review concludes that, in certain subgroups of patients with breast cancer (ie, patients with primary tumors larger than 5 cm, four or more positive axillary lymph nodes, or tumor involvement of the pectoralis fascia), postmastectomy irradiation improves local control and may result in a modest increase (10% or less) in the breast cancer-specific survival rate. The paradigm that survival from breast cancer depends on the eradication of occult micrometastases has led to a debate about the extent of local therapy (surgery and/or irradiation) that is necessary. Today, with the increasing use of induction (preoperative) chemotherapy for tumor downstaging, the role of local therapy is becoming one of controlling residual disease with an acceptable locoregional relapse rate and minimal disfigurement or morbidity.

In surgery, this issue is exemplified by the recent questioning of the necessity of axillary node dissection if systemic therapy is planned on the basis of the features of the primary tumor rather than on the basis of axillary nodal status. As with postmastectomy irradiation, a breast cancer-specific survival benefit, if any, from the axillary node dissection itself is probably small (less than 10%). The concern then becomes local control. Can systemic therapy substitute for local therapy (eg, axillary node dissection) if the axilla is clinically negative? As this review shows, systemic therapy may decrease the locoregional recurrence rate, at least in certain patient subsets. However, if the risk of locoregional recurrence is high (20% to 30% relapse rate), the addition of irradiation to systemic therapy provides optimal local control (5% to 10% relapse rate).

Clinical Significance of Reduced Locoregional Failure Rate

Is this additional reduction in the locoregional failure rate clinically significant? The answer depends on whether the locoregional relapse can be effectively treated if it occurs.

The likelihood of reestablishing local control of the postmastectomy chest wall with delayed irradiation is only approximately 50%. Although locoregional recurrence after mastectomy has historically been considered a harbinger of distant metastases and subsequent death, selected patients with locoregional recurrence experience a long distant disease-free interval and occasionally long-term survival. The emotional impact on the patient of experiencing a locoregional recurrence, especially as the first site of relapse, should also be considered. Thus, the goal of local control is best pursued at the initial treatment of the primary tumor.

Does this goal of local control outweigh the potential side effects of irradiation? With the recent advances in radiation technology, the overall morbidity of postmastectomy irradiation has substantially decreased. However, further follow-up is needed to determine whether the risk of cardiovascular disease associated with irradiation of the left chest wall will also decline.

Our practice guidelines at The University of Texas M. D. Anderson Cancer Center call for postmastectomy irradiation for patients with tumors larger than 5 cm, four or more positive axillary nodes, positive surgical margins, dermal lymphatic involvement, or direct skin invasion. We do not use irradiation for patients with microscopic extranodal axillary disease or small multicentric primary tumors. As Fowble states, irradiation of the internal mammary nodes for assumed occult disease has largely been abandoned as clinically irrelevant.

Finally, the patient's personal goals must be incorporated into the treatment plan. An honest, open discussion of the disease and the anticipated results from different treatment modalities often empowers the patient to become an active participant in the decision-making process.

 
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