The presence of ductal carcinoma in situ (DCIS), the most common type of non-invasive breast cancer, and young age are associated with increased risk of tumor recurrence on the same side of the body after treatment with breast-conserving therapy, according to a long-term follow-up of the EORTC “boost no boost” clinical trial.

The European Organisation for Research and Treatment of Cancer (EORTC) study, “Prognostic Factors For Local Control in Breast Cancer After Long-term Follow-up in the EORTC Boost vs No Boost Trial,” published in JAMA Oncology, also reveals that while the association of high-grade invasive tumors with recurrence decreased after five years, the effect of DCIS adjacent to invasive tumor-in-tumor recurrence remained stable over time, suggesting that those with DCIS require longer follow-up times.

The randomized Phase 3 EORTC “boost no boost” clinical trial (NCT02295033) was designed to evaluate the effects of an extra dose of radiation therapy (boost dose) after breast-conserving surgery and adjuvant radiation therapy. The study showed that adding the extra dose of whole-breast irradiation had no effect on long-term overall survival, but improved local control, compared to those who only received the breast-conserving surgery and adjuvant radiation therapy.

Earlier analysis of the EORCT boost no boost trial revealed that young age and high-grade tumors were associated with a higher risk of local recurrence after treatment, but the recurrence rate could be reduced with the extra radiation therapy dose, particularly in young patients.

In the follow-up study, a team of researchers led by Conny Vrieling, MD, PhD, of the Clinique des Grangettes, Switzerland, sought to reanalyze the prognostic factors related with breast cancer recurrence in a long-term follow-up of the EORCT boost no boost trial. They examined data from 1,616 patients who had been included in the trial, 801 of whom were given no boost, and 815 who received the radiation therapy boost.

Results showed that 160 patients had recurrence of their breast cancer over the trial period, accounting for a 20-year cumulative incidence of 15%. After adjusting for other known prognostic factors, investigators found those with DCIS had a 2.15-fold increase in their risk for recurrence. Young age also was significantly associated with recurrence, with 34% of women younger than 30 having recurred, a percentage that decreased to 11% in women from age 30 to about 50, and stabilized by age 50.

But the researchers found that adding the extra dose of radiation therapy in patients younger than 50 reduced the 20-year cumulative incidence of recurrence from 24 percent to 15 percent. In patients with DCIS, the boost also significantly decreased the 20-year cumulative incidence of breast cancer recurrence from 22% to 14%.

Those with both risk factors saw their 20-year cumulative incidence of recurrence decreasing from 31% to 15% when the radiation boost was added.

The study also showed that patients with high-grade invasive tumors had increased risk of recurrence in the first five years of follow-up, but this effect declined over time. In these patients, the boost therapy also showed benefits, decreasing the 15-year cumulative incidence of recurrence from 31% to 5%.

Together, the results reveal that the prognostic value of certain factors may change over time after breast-conserving therapy.

“Patients with high-grade invasive tumors should be monitored closely, especially in the first five years. The impact of DCIS remained constant over time, indicating that long-term follow-up is necessary. The boost significantly reduced IBTR [recurrence] in these patients,” the researchers wrote.