Post-operative radiotherapy was found to reduce the risk of invasive cancer recurrence in the same breast by 70 percent, while treatment with tamoxifen lowered the risk of same-breast recurrence by 30 percent, according to a study published in the December issue of The Lancet.
Previous results from the UK/ANZ DCIS (ductal carcinoma in situ) study had assessed the effects of post-excision treatment of DCIS with radiotherapy, treatment with tamoxifen and both. After a median follow-up of 4.4 years, radiotherapy was found to lower the incidence of ipsilateral invasive disease and ipsilateral DCIS significantly, while tamoxifen was weakly associated with a reduction in all new breast events without any lowering of invasive cancer incidence.
The present study sought to measure the longer-term effects of radiotherapy and tamoxifen on the same study population, patients with excised DCIS. The study randomly grouped 1,694 patients into four cohorts: 544 persons received neither radiotherapy nor tamoxifen; 567 patients took tamoxifen alone; 267 underwent radiotherapy only; and 316 patients underwent radiotherapy as well as treatment with tamoxifen.
Within the median follow-up of 12.7 years, 376 of the 1,694 women experienced additional breast events; 197 of these represented DCIS, 163 were invasive cancers and 16 events were of unknown diagnoses. Significantly fewer breast events occurred in patients assigned to receive tamoxifen (151 total) than in those who did not take the drug (204). The tamoxifen group also had a hazard-ratio of .71.
Radiotherapy significantly decreased the likelihood of recurring breast events, with an absolute reduction over the 12.7-year follow-up period of 12.6 percent. A total of 60 new breast events were observed in the 522 patients randomized to receive radiotherapy, while non-radiotherapy patients, a total of 508, experienced 129 breast events.
Four percent of radiotherapy patients experienced recurrence of DCIS, compared with 11.6 percent of non-radiotherapy patients. For patients who took tamoxifen, 9.2 percent experienced a recurrence of DCIS, versus 13.6 percent of those who did not take the drug.
The authors found that women with high grade and large-sized tumors, as well as younger patients, were significantly more likely to experience recurrences. Moreover, tamoxifen "seemed to be more effective in women with low-grade or intermediate-grade tumors," according to Jack Cuzick, PhD, of Queen Mary School of Medicine and Dentistry, at the University of London, and colleagues. "There was a weak effect of radiotherapy in those with intermediate-grade or high-grade tumors....[and] radiotherapy was more effective in women over 50 years old than in those under 50 years old."
Cuzick and co-authors concluded that "[t]his updated analysis confirms the long-term beneficial effect of radiotherapy and reports a benefit for tamoxifen in reducing local and contralateral new breast events for women with DCIS treated by complete local excision."