WEDNESDAY, March 27, 2024 (HealthDay News) — For young breast cancer patients after complete excision, high- versus low-dose radiation yields slightly better local control but increased incidence of marked or moderate fibrosis in the boost area, according to a study presented at the annual European Breast Cancer Conference, held from March 20 to 22 in Milan.

Sophie Bosma, M.D., Ph.D., from The Netherlands Cancer Institute in Amsterdam, and colleagues presented the results of a 10-year primary analysis involving patients aged 50 years and younger with pT1-2, pN0-2a invasive breast cancer after complete excision. Participants were randomly assigned to receive a boost of 26 Gy or 16 Gy (high or low) to the tumor bed (1,211 and 1,210 patients, respectively). The primary end point was local control at 10 years, assuming significance as a 3.5 percent difference at 10 years.

The researchers found that overall, there were 109 local recurrences (61 and 48 with low and high boost, respectively). Local recurrence was the first event for 42 and 23 patients in the low- and high-boost arms, respectively. The 10-year local recurrence rate was 4.4 and 2.8 percent for patients treated with a low and high boost, respectively (hazard ratio, 0.61). Boost dose, final margin status, subtype, and chemotherapy use were factors significantly associated with local recurrence in a multivariable analysis. The cumulative incidence of marked or moderate fibrosis in the boost area was 27 and 48 percent for patients treated with low and high boost, respectively.

“In both groups local recurrence rates were very low and much better than expected,” Bosma said in a statement. “Although we did find a difference between the two groups in terms of the recurrence rate, this was a small difference which must be weighed against the increase in side effects, such as fibrosis.”

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