Although radiation therapy following lumpectomy for lymph node-negative
breast cancer significantly reduces both local and distant disease
recurrence, overall mortality is not substantially better in women
who receive radiation than in those who do not, according to a
Canadian study update report in the November 20th Journal of the
National Cancer Institute.
Researchers Roy M. Clark, md, Mark Levine, md, and other members
of the Ontario Clinical Oncology Group add that no subgroup of
patients was found to have a low enough risk of local disease
recurrence to suggest that other women with similar disease characteristics
might safely forego post-lumpectomy radiation therapy.
The authors note that breast-conservation surgery is now commonly
used in the management of early-stage breast cancer, and clinical
trials have demonstrated that breast irradiation after surgery
substantially reduces the risk of cancer recurrence in the breast.
In this study, 837 women in Ontario diagnosed, from April 1984
Through Februrary 1989, with breast cancer that had not spread
to axillary lymph nodes were treated with lumpectomy and were
then randomly assigned to receive radiation therapy to the affected
breast or no further treatment. None of the women in the study
received postsurgical systemic therapy.
Initial results of the study were published in 1992 after a median
follow-up time of 43 months. At that time, recurrence of cancer
in the breast occurred in 5.5% of patients who received breast
irradiation compared with 25.7% of those who did not. No difference
in survival was detected between the two groups. In addition,
a low-risk patient subgroup (ie, less than a 10% chance of local
disease recurrence without radiation therapy) for whom irradiation
might not be necessary could not be identified.
The current report updates findings now that the median patient
follow-up has reached 7.6 years. Eleven percent of the irradiated
patients have experienced a recurrence of cancer in the breast,
as compared with 35% of women not receiving radiotherapy. Women
not receiving radiotherapy had a fourfold greater risk of local
recurrence relative to those receiving the treatment. This difference
was highly statistically significant. Radiation therapy also resulted
in a statistically significant decrease in relapse at sites distant
from the primary tumor. As in the initial data analysis, younger
age (less than 50 years), tumor size (greater than 2 cm), and
poor nuclear grade were found to be important predictors for local
Also as before, however, there was no statistically significant
difference in overall survival between the two patient groups,
and tumor size and tumor grade remained key predictors for mortality.
Similarly, no low-risk subgroup could be identified who might
not require radiation therapy.
The authors acknowledge that the failure of radiation therapy
to improve overall survival while reducing local and distant relapse--demonstrated
in this and other studies--remains difficult to explain. Possible
explanations, they suggest, may involve the limited power of individual
studies to date to detect a statistically significant survival
difference, the possibility that radiotherapy reduces breast cancer
mortality but increases mortality due to other causes (eg, ischemic
heart disease), or that the high metastatic potential of breast
cancer prevents any real benefit from radiotherapy on survival.
Finally, Clark and coworkers note that, even if a low-risk group
could be identified, radiation therapy is still likely to be effective.
Individual decision-making, they say, will relate to the perceived
value of potential benefits (eg, disease-free survival) balanced
against possible adverse effects (eg, long-term radiotherapy-related
morbidity) . Tumor size and nuclear grade, they add, should continue
to be used as prognostic markers to guide the use of adjuvant