Postmastectomy RT to Axillae Often Unnecessary

SAN ANTONIO—Follow-up studies from five clinical trials at M.D. Anderson suggest that postoperative supplemental radiotherapy to the axillae in patients with stage II-III breast cancer is often unnecessary, since failure in the dissected axillae is uncommon. The report was presented at the 23^rd annual San Antonio Breast Cancer Symposium.

Postmastectomy irradiation to the axillae has been shown in three trials not only to improve local-regional control but also to potentially improve survival in patients at high risk for failure.

The indications for this approach at M.D. Anderson are the involvement of four or more axillary lymph nodes, tumor size greater than 5 cm, or 2 mm or more of extranodal extension.

While the chest wall is always irradiated in these patients, indications for radiation to the regional nodes in addition to the chest wall are somewhat controversial, explained Angela Katz, MD, a radiation oncologist at M.D. Anderson and the study’s lead investigator.

The aim of this retrospective review of 1,031 patients was to determine if there is a subgroup of patients for whom postoperative regional nodal irradiation after surgery is particularly beneficial and to identify patients for whom specialized radiation fields should be added, she said.

The study was based on the regional nodal failure patterns of patients with stage II-III breast cancer treated in M.D. Anderson clinical trials from 1975 to 1994 and followed for almost 10 years.

The women had tumors of 2.5 cm; median age was 49 years. They received definitive surgery (mastectomy, including a level I-II axillary dissection) and doxorubicin-based systemic therapy but no radiotherapy.

Patient records were reviewed and all regional recurrences, including isolated failures as well as failures with or without distant metastases, were recorded.

There were 141 node-negative patients, 466 patients with one to three positive nodes, and 319 patients with four or more involved nodes.

Ten-year overall survival for the group was 65%; disease-free survival was 55%; 19% of patients had a local-regional recurrence. There were 179 local-regional occurrences, of which 124 were isolated events without distant metastases. Sixty-four percent of patients were free of distant metastases at 10 years, Dr. Katz reported.

Local-Regional Recurrence Patterns

The 179 local-regional failures were in the following sites: 68% chest wall, 40% supraclavicular nodes, 14% axillae, 7% intraclavicular nodes, and 8% internal mammary nodes. More than one site could be involved.

Failure in the dissected axillae, however, was rare, occurring in only 25 patients, for a 10-year actuarial rate of 3% in this group. Of these, 17 were isolated regional failures.

"None of the factors we looked at predicted for a higher rate of failure in the dissected axillae, including the number of involved nodes, an increasing percentage of involved nodes, larger nodal size, the presence of extranodal or extracapsular extension, or the extent of the axillary dissection," she said.

Failure in the undissected axillae or the supraclavicular area was more common, occurring in 75 patients for an 8% rate at 10 years.

Significant predictors of failure in this group of patients included the involvement of at least four axillary lymph nodes, involvement of 20% of the nodes examined, and the presence of 2 mm or more of extranodal extension. Ten-year actuarial failure rates for patients with these factors were 15%, 14%, and 20%, respectively, Dr. Katz reported.

"Patients with 2 mm or more of extranodal extension are at increased risk of local-regional recurrence. However, most of these recurrences involve the chest wall (74%) or the undissected axillae (50%)," Dr. Katz said.

She noted that failure in the dissected axillae does not appear to be increased in these patients. "It is only 5% at 10 years, or 12% of the failures in these patients. So extracapsular extension appears to be a marker of more aggressive disease but not necessarily of disease left in the axillae," she said.

The findings suggest that failure in the dissected axillae is uncommon, she said. "Supplemental radiotherapy, therefore, is rarely warranted in these patients, and extracapsular extension is not an indication for it," she said.

Indications for irradiation to the undissected axillae in addition to the chest wall include the presence of four or more involved nodes, involvement of more than 20% of the nodes examined, or at least 2 mm of extranodal extension, she reiterated.