ESTRO 2024 - Abstract Book

S671

Clinical - Breast

ESTRO 2024

We included patients diagnosed with primary breast cancer (BC) who underwent IOERT at a single institution in the period 2000-2016. The primary outcome was LR rate, including events either in the same quadrant as the primary BC or in other quadrants of the ipsilateral breast, with or without synchronous nodal involvement or distant metastasis. Statistically significant predictors for LR were identified at univariate and multivariate (MV) analyses. A predictive nomogram based on logistic model was generated. The nomogram was internally validated for discrimination and calibration using Hosmer& Lemeshow Goddness of fit method

Results:

A total of 3397 patients were analyzed. AT MV analysis, predictors for LR were incorporated into the nomogram and included younger age, histologic subtype, tumor size ≥ 1.5 cm, tumor grade 2 -3, ER and PR negative status, nodal involvement, molecular subtype other the Luminal A and HER 2positive receiving anti-HER2 therapy . At 6.1 years median FU (range 4.3-8.0) there were 265 local events (7.8%) resulting in a LR cumulative incidence (CIF) of 4.4% ( 95% CI 3.7-5.2) at 5 years and 13.5% (95% CI, 11.7-15.5) at 10 years. Internal validation was performed on the IOERT arm of the ELIOT phase III randomized trial (585 women). Calibration plots showed that the observed proportion of LR in the ELIOT arm well fit with the expected proportion as predicted by the logistic models at 5 years ( 26 CIF observed vs 23.9 CIF predicted, Chi square= 8.38 with 9D, p= 0.50 , while for 10 years the estimated probability was not so close to the probability observed in the data, even if the difference was not significant (49 CIF observed vs 69.8 CIF predicted, Chi square= 9.91 with 9 D , p=0.36)

Conclusion:

The nomogram-predicted results were well fitted to the actual outcomes in an internal validation using the ELIOT trial population, with a better risk prediction at 5 years. The model can be an useful tool for guiding treatment decision making for patients candidates to IOERT

Keywords: Nomogram, Intraoperative Radiotherapy

References:

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