Postmastectomy Radiation: Then and Now

Dr. Fowble's well-written review concludes that, in certain subgroupsof patients with breast cancer (ie, patients with primary tumors largerthan 5 cm, four or more positive axillary lymph nodes, or tumor involvementof the pectoralis fascia), postmastectomy irradiation improves local controland may result in a modest increase (10% or less) in the breast cancer-specificsurvival rate. The paradigm that survival from breast cancer depends onthe eradication of occult micrometastases has led to a debate about theextent of local therapy (surgery and/or irradiation) that is necessary.Today, with the increasing use of induction (preoperative) chemotherapyfor tumor downstaging, the role of local therapy is becoming one of controllingresidual disease with an acceptable locoregional relapse rate and minimaldisfigurement or morbidity.

In surgery, this issue is exemplified by the recent questioning of thenecessity of axillary node dissection if systemic therapy is planned onthe basis of the features of the primary tumor rather than on the basisof axillary nodal status. As with postmastectomy irradiation, a breastcancer-specific survival benefit, if any, from the axillary node dissectionitself is probably small (less than 10%). The concern then becomes localcontrol. Can systemic therapy substitute for local therapy (eg, axillarynode dissection) if the axilla is clinically negative? As this review shows,systemic therapy may decrease the locoregional recurrence rate, at leastin certain patient subsets. However, if the risk of locoregional recurrenceis high (20% to 30% relapse rate), the addition of irradiation to systemictherapy 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 clinicallysignificant? The answer depends on whether the locoregional relapse canbe effectively treated if it occurs.

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

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

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

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