Vaidya, JS; (2013) Case selection for targeted intraoperative radiotherapy (TARGIT). Presented at: European Cancer Congress 2013 (ECCO-ESMO-ESTRO), Amsterdam, Netherlands.

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Abstract

Background: The TARGIT-A randomised trial compared a risk-adapted approach using targeted intraoperative radiotherapy (TARGIT) with whole breast external beam radiotherapy (EBRT) after lumpectomy for early breast cancer. At the San Antonio update, it was suggested that the preferred option is to give TARGIT concurrently with lumpectomy (prepathology). In this analysis we describe patient and tumour factors that may help select patients for TARGIT based on the results of an a priori statistical analysis plan. Methods: In this large international trial, 3451 patients (age>=45, unifocal invasive ductal carcinoma, size 3.5 cm) from 33 centres in 10 countries were randomly allocated to either TARGIT or EBRT. Primary outcome was ipsilateral breast recurrence and secondary included mortality. Before unblinding for this analysis, we hypothesised that progesterone receptor (PgR) status, as an expression of a functionally active oestrogen receptor (ER), is a surrogate for radiation responsiveness and could predict a difference between the outcome for local control in the two randomised groups and pre-specified a detailed analysis by PgR status. We also assessed whether a Cox proportional hazard model including age, margin status, tumour grade, ER, PgR, HER2, vascular invasion and node positivity was consistent with our results. Results: For PgR positive cases, there was no significant difference in the primary outcome of Ipsilateral breast recurrence between TARGIT and EBRT (2.3%(1.3−4.3) vs. 1.5%(0.75−3.0) p = 0.51, while in PgR negative cases there were significantly more local recurrences after partial breast irradiation using TARGIT: 7.0%(3.5–13.6) vs. 0.5%(0.1−3.7) p = 0.017. By contrast, age, margin status, tumour grade, tumour size, vascular invasion, node positivity, ER and Her2 status were not found to be significant predictors. Even age younger than 50 or grade 3 cancers had similar outcome with TARGIT or EBRT. Exploratory analyses in conjunction with the timing of TARGIT, revealed that when TARGIT was given concurrently in PgR positive cases (n=1625) the results were (TARGIT vs. EBRT): ipsilateral breast recurrence 4 vs. 5, 5-year risk 1.4%(0.46−3.9) vs. 1.2%(0.48−2.9) HR 0.82(0.22–3.06), and overall mortality 18 vs. 31, 5-year risk 3.3%(1.83–6.04) vs. 6.4%(4.3−9.6) HR 0.60(0.34–1.08). Conclusions: It appears that progesterone receptor status is useful in selecting cases for using the TARGIT concurrently with lumpectomy for breast cancer. Progesterone receptor negative patients may fall in the cautious or unsuitable category and progesterone receptor positive cases are in the suitable category for partial breast irradiation with TARGIT. Conflict of interest: Other substantive relationships: Carl Zeiss (travel to meetings and honoraria).

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