Postmastectomy RT in Node+ Patients Reduces Locoregional Recurrence

NEW ORLEANS—Radiation therapy after mastectomy reduces locore-gional recurrence rates for breast cancer patients with positive lymph nodes, positive surgical margins, or both, according to the results of a large retrospective study presented at the 44th Annual Meeting of the American Society for Therapeutic Radiology and Oncology (ASTRO abstract 153).

Certain Patients Benefit

"According to our data, there are certain patients who can greatly benefit from postmastectomy radiation," said lead investigator Wendy A. Woodward, MD, PhD, a resident in the Department of Radiation Oncology, M.D. Anderson Cancer Center. "Patients whose cancer involves 20% or more of the removed lymph nodes or who have close or positive surgical margins can significantly reduce their chances of a recurrence with postoperative radiation therapy."

Postmastectomy radiation reduces locoregional recurrence for all patients with breast cancer, Dr. Woodward said. However, determining what threshold of risk warrants the risks associated with treatment remains controversial. Finding patterns and predictors of locoregion-al recurrence can help determine which patients should emphatically be offered postoperative radiation therapy, she said.

The study patients—drawn from five prospective trials totaling 1,800 patients—were treated with mastectomy followed by doxorubicin-based chemotherapy. Results from the 469 patients who received postoperative radiation therapy were compared with those of the 1,031 patients who did not. Median follow-up was 10 years.

Study Results

Postmastectomy radiation therapy reduced isolated (without distant metasta-ses) locoregional recurrence rates for all patients regardless of the number of nodes involved. This benefit occurred despite the less favorable prognostic factors of the patients who received radiation therapy, including greater tumor size, higher tumor stage, and increased number of positive nodes, Dr. Woodward said.

For all patients treated with postmas-tectomy radiation, the total locoregional recurrence rate (with or without distant metasta-ses) was 10%, compared with 19% for the patients who did not receive postmas-tectomy radiation, Dr. Woodward reported.

Looking specifically at the subset of 502 patients with T1-T2 stage tumors with one to three positive nodes, the investigators found that freedom from locoregional recurrence in patients treated with radiation was 97% vs 87% for patients not treated with radiation.

"This is one of the first studies to demonstrate this reduction in patients who have adequate axillary dissection as well as doxorubicin-based chemotherapy," she said. "We feel that our data strongly endorse enrollment in the ongoing Intergroup trial to determine the magnitude and benefit of postmastectomy radiation therapy in terms of locoregional recurrence as well as overall survival for patients with T1 or T2 stage tumors and one to three positive lymph nodes."

T3-T4 Tumors or 4 Positive Nodes

The investigators also looked at the group of patients for whom radiation therapy would be routinely recommended—those with T3-T4 tumors or at least four positive lymph nodes. In these patients, freedom from locoregional recurrence was seen in 93% who received postmastectomy radiation vs 60% who did not.

For patients with 20% or more involved lymph nodes, the locoregional recurrence rate was reduced from 27% in patients who did not receive radiation to 11% in those treated with radiation, Dr. Woodward reported. For patients with fewer than 20% involved nodes, the locoregional recurrence rate fell from 12% to 4.2% with use of postmastectomy radiation therapy.

The locoregional recurrence rate for patients with close or positive margins was 13.3% in those who received postoperative radiation and 45% in patients treated without radiation.

The chest wall and supraclavicular fossa were the most common sites of loco-regional recurrence, Dr. Woodward pointed out. The percentage of chest wall recurrences fell from 68% without postmastectomy radiation therapy to 6.4% with radiation therapy. Supraclavicular recurrences fell from 41% to 3.4%.

Positive estrogen-receptor status was found to be the strongest independent predictor of locoregional recurrence in patients treated with radiation therapy. These patients were 17% more likely to have locoregional recurrence, she said. Pathologic size of the largest involved node and lymph-vascular space invasion were also significant predictors in this group.