Adjuvant Radiotherapy Reduces Recurrences With Small Breast Tumors

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Elsevier Global Medical News. 2009 Jun 30, K Wachter


ORLANDO (EGMN) - The use of adjuvant radiation therapy following mastectomy reduced the risk of locoregional and distant recurrence among breast cancer patients with tumors measuring less than 5 cm and with one to three positive lymph nodes, particularly for patients with T2N1 disease, in a retrospective study of more than 3,700 women.
Overall, women who did not receive radiation therapy after mastectomy had a statistically significant 38% greater relative risk of distant recurrence (hazard ratio, 1.38; P = .0018), compared with women who had segmental resection and radiation therapy, Dr. Shaheenah S. Dawood reported at the annual meeting of the American Society of Clinical Oncology.
Although the difference was not statically significant, they also had a 26% greater relative risk of locoregional recurrence (HR, 1.26; P = .11).
The current consensus is that postmastectomy radiation therapy is indicated for patients whose tumors are greater than 5 cm or who have at least four positive lymph nodes. The use of adjuvant radiation therapy when early-stage patients with smaller tumors and fewer positive nodes are treated with mastectomy and systemic therapy remains controversial, noted Dr. Dawood of the department of oncology at the Dubai (United Arab Emirates) Hospital.
In this retrospective study, the researchers compared locoregional and distant recurrences between women with stage I/II breast cancer who had undergone a mastectomy without radiation therapy vs. women who had segmental resection followed by radiation therapy. The investigators chose this design because historically mastectomy was not followed by radiation therapy, and the study would not have had a valid comparison group of patients who underwent mastectomy plus radiation therapy.
The researchers used data from a database of patients treated for breast cancer at the University of Texas M.D. Anderson Cancer Center in Houston. They included female patients, diagnosed between 1980 and 2007, who had T1/T2 NO or T1/T2 N1 disease (that is, tumors smaller than 5 cm and with fewer than four positive lymph nodes). They excluded the few patients who had undergone mastectomy with radiation therapy or segmental resection without radiation therapy. The cutoff for follow-up was Dec. 30, 2008.
A total of 1,585 women had mastectomy without adjuvant radiation, and 2,155 women had segmental resection followed by radiation therapy. A greater proportion of women in the mastectomy-only group had node-positive disease, compared with the radiation group. At the time of this analysis, 18% of the entire population had died. Median overall survival for the entire cohort was 161 months. The 5-year distant disease-free survival rate was 78%; and the 5-year locoregional disease-free survival rate was 88%.
In the multivariate analyses, the researchers controlled for age, grade, hormone receptor status, HER2 status, menopausal status, race, neoadjuvant chemotherapy, anthracycline use, taxane use, and lymphovascular invasion. The findings were as follows:
- Node-negative tumors. For the 1,191 patients with T1N0 disease, the 5-year locoregional disease-free survival estimates were almost identical: 92% with radiation and 91% without. For the 997 women with T2N0 disease, these 5-year estimates were a close match: 91% with radiation and 89% without.
The 5-year estimates for distant disease-free survival were also similar for patients with T1N0 disease (87% with radiation and 86% without) and those with T2N0 disease (85% with radiation and 80% without).
- Node-positive tumors. Among 876 patients with T1N1 disease, the 5-year locoregional disease-free survival estimates were almost identical as well: 91% with radiation and 90% without. There was a significant difference, however, among 676 women with T1N2 disease: 91% with adjuvant radiation vs. 87% without (P = .009).
The 5-year distant disease-free survival estimates were significantly different for both groups: 90% with radiation and 85% without among patients with T1N1 disease (P = .004); 77% with radiation and 68% without among women with T1N2 disease (P = .0177).
"The benefit of radiation appears to be most pronounced for patients with T2N1 disease, with the benefit still unclear for those with T1N1 disease," Dr. Dawood said. When radiation was given, women with T2N1 disease had a hazard ratio of 3.0 (P = .0008) for locoregional disease-free survival, and 1.71 (P =.0007) for distant disease-free survival.
The researchers acknowledged the limitations of their study - its retrospective nature and less-than-ideal comparison groups - but consider the results to be hypothesis generating.
The authors reported that they had no relevant financial relationships.

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