Patterns of ipsilateral breast tumor recurrence following partial vs. whole-breast irradiation: a retrospective...

Partial-breast irradiation (PBI) is an alternative to whole-breast irradiation (WBI) in breast-conserving therapy. This study evaluated the incidence and temporal patterns of ipsilateral breast tumor recurrence (IBTR), classified as true recurrence (TR) or new primary tumor (NP), and compared the impact of PBI and WBI.

We retrospectively analyzed 1,395 patients treated with PBI or WBI between 2008 and 2024. PBI was delivered perioperatively using multicatheter interstitial brachytherapy (32 Gy in 8 fractions or 25.2 Gy in 4 fractions) or WBI (50 Gy in 25 fractions). The incidence, timing, and predictors of TR and NP were evaluated.

At a median follow-up of 6.7 years, 40 IBTRs (2.9%) occurred: 20 TRs (1.4%) and 20 NPs (1.4%). Five- and 10-year breast cancer-specific survival rates were 85.4% and 60.1% for TR, and 100% and 100% for NP (p < 0.01). TR rates were similar between the PBI and WBI cohorts (1.4% vs. 1.6%, p = 0.68), but NP occurred more frequently after PBI (1.9% vs. 0.5%, p = 0.04). Multivariate analysis revealed that younger age (< 50 years) was independently associated with TR (HR, 2.51; p = 0.01), and PBI was significantly associated with NP (HR, 4.44; p < 0.01).

PBI provides local control comparable to WBI for TR; however, it may be associated with an increased risk of NP, which represents a potential drawback of PBI.