Partial-breast radiotherapy maintains tumor control, reduces late toxicity
medwireNews: Partial-breast and reduced-dose radiotherapy are noninferior to the whole-breast equivalent for the prevention of local relapse in women with early breast cancer, UK IMPORT LOW trial data show.
In addition, women receiving partial-breast radiotherapy reported fewer adverse events, including changes in breast appearance and breast hardness, than those receiving whole-breast radiotherapy.
“These findings support our hypothesis that partial-breast radiotherapy using a standard radiation technique can reduce late toxicity without jeopardising local tumour control,” write Charlotte Coles (University of Cambridge, UK) and co-investigators in The Lancet.
They report that, after a median 72.2 months of follow-up, nine (1.3%) of 674 women who were randomly assigned to receive 40 Gy whole-breast radiotherapy in 15 daily fractions (control group) experienced local relapse.
Local relapse also occurred in three (0.44%) of 673 women assigned to treatment with 36 Gy whole-breast radiotherapy and 40 Gy to the partial breast (reduced-dose group) and six (0.90%) of 669 women assigned to receive 40 Gy to the partial breast only (partial-breast group).
All of the women in IMPORT LOW were aged 50 years or older and had undergone breast-conserving surgery for grade 1–3 unifocal invasive ductal adenocarcinoma (pT1–2, pN0–1) with non-cancerous tissue microscopic margins of at least 2 mm.
The estimated cumulative incidence of local relapse at 5 years was 1.1% in the control group, 0.2% in the reduced-dose group, and 0.5% in the partial-breast group.
The estimated absolute differences in local relapse were −0.73% and −0.38% for the reduced-dose and partial-breast groups, respectively, compared with the control group.
Coles and team say that this means “non-inferiority can be claimed for both reduced-dose and partial-breast radiotherapy” because the upper limit of the 95% confidence intervals “ruled out a greater than 2.5% increase in local relapse risk for each of the test schedules.”
In addition, photographic, patient, and clinical assessments recorded showed fewer normal tissue adverse effects with partial breast versus whole-breast radiotherapy. Specifically, patients in the former group reported significantly less change in breast appearance and significantly less breast hardness than those in the latter group.
The researchers conclude: “This method of partial-breast radiotherapy seems to be safe and effective and could be implemented easily within most radiotherapy centres worldwide.”
They add: “Follow-up is continuing and 10-year local relapse incidence and toxicity will be reported in future.”
Commenting on the report, Reshma Jagsi, from the University of Michigan in Ann Arbor, USA, suggests that “the most striking finding of IMPORT LOW is not simply that of non-inferiority but rather the extremely low absolute recurrence rates observed across all groups,” which she says again highlights “the question of whether some other patients might also reasonably omit radiotherapy.”
She adds that “the findings of IMPORT LOW support ongoing efforts… to establish whether improvements in other disciplines (eg, imaging, pathology, surgery, and systemic therapy) might now render adjuvant radiotherapy immediately after breast-conserving surgery to be optional for an even larger, identifiable subgroup of patients who are not currently given this option.”
“In summary, efforts to minimise toxicity and burden of treatment are increasingly important in an era of falling recurrence risks. Future generations of women diagnosed with breast cancer will benefit not only from the findings of the IMPORT LOW trial itself but also from the advances that will build on its foundational efforts,” Jagsi concludes.
By Laura Cowen
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