NSABP-B04 demonstrated that radiation, in lieu of axillary dissection, for patients with clinical N0 or N1 breast cancer was adequate treatment and secured local control in the majority of patients.

Currently, most patients require axillary staging to direct systemic therapy. In the case of elderly patients who are not medially fit for chemotherapy, and in cases when the primary tumor, upon excision, is demonstrated to be hormone-receptor positive and, therefore, utilization of hormonal therapy is indicated, axillary dissection is not necessary. For patients who will undergo radiation as a component of their therapy, it is technically quite simple to include levels 1 and 2 of the axilla. In this circumstance, the inferior aspect of the humoral head is the desired superior border of the radiation field. This represents a very minor alteration in the standard radiation field and should be considered as an appropriate alternative to axillary surgery in this select population.

Postmastectomy Radiation Therapy

Among patients who undergo mastectomy for early-stage breast cancer (StageI and Stage II) the role of postmastectomy radiation is currently in evolution. At one point in time, this was the only adjuvant therapy available and it was clearly effective in diminishing local failure.

With longer follow-up on the rather simple radiation techniques from the 1950s and 60s, however, it has become evident that cardiovascular deaths, particularly for patients treated for left-sided tumors, were a significant cause of long-term mortality.  Therefore, postmastectomy radiation therapy fell out of favor as chemotherapy became more commonly utilized among patients with breast cancer.

It has become evident that chemotherapy alone has little impact upon local failure rates in certain patients with a variety of unfavorable prognostic factors.  Local control in the chest-wall region clearly benefits from the addition of radiation to combined-modality treatment.

At our institution, patients with primary tumors 5 cm or greater in dimension, four or more positive axillary lymph nodes or positive margins of resection are referred for postmastectomy radiation therapy. Recent randomized studies from Canada and Europe suggest that the indications for postmastectomy radiation should be extended to all node-positive patients.

These studies have certain flaws in as much as the local failure rate among patients who underwent mastectomy alone is considerably higher than one would expect. The number of axillary lymph nodes removed is considerably lower than one would expect, and the adequacy of local surgical managemen in these studies is called into question. Nevertheless, the investigators did demonstrate an improvement in survival among patients who underwent postmastectomy chest-wall radiation and further investigation on this topic is merited.

Currently, postmastectomy chest-wall radiation remains an area o controversy, but patients with positive margins, primary tumors of 5 cm or more in dimension and four or more positive lymph nodes clearly benefit in terms of local control. The impact on survival will have to awai further randomized studies.

The radiation-therapy technique for postmastectomy radiation is considerably different than that utilized for the intact breast. Tangential fields may be utilized; however, these do not reliably cover the internal mammary lymph nodes. As local-regional lymphatic permeation is a factor in the high risk of local-regional failure, adequate peripheral lymphatic radiation is considered desirable.

Furthermore, the skin dose in this setting is 100% of the prescribed dose, whereas in the breast-conservation setting, the skin dose is approximately 70%. This is felt to be adequate, as skin failures in patients treated with breast-conservation therapy are extremely rare. On the other hand, in patients who have undergone mastectomy, the scar and surrounding skin are the most common area for failure and 100% of the prescribed dose to the skin must be delivered. Therefore, the utilization of dose modifying techniques to assure a 100% dose to the skin is mandatory.

This results, logically, in much more severe skin reactions. Again, meticulous attention to skin care is critical from the outset if therapy is to be delivered without interruption. This involves the copious use of emollients, as well as refraining from wearing either restrictive clothing or a breast prosthesis Between 30-50% of patients will have some element of moist desquamation that will almost always resolve with conservative management.

Rather complicated treatment planning is required to adequately trea the chest wall, skin and peripheral lymphatics without delivering an undesirably high dose to the underlying lung, heart and brachial plexus. Custom electron plans are extremely effective at permitting a conformal dose over the region of the internal mammary lymph nodes while permitting greatest possible limitation of the dose to the lung and the heart, once again highlighting the importance of a customized approach to each patient’s treatment needs. Standard postoperative chest-wall therapy consists of 50Gy in approximately 5 weeks of daily treatment, Monday through Friday. Under most circumstances, the scar is boosted to a total dose of 60 Gy.

Karen D. Schupak
American College of Physicians

References