Purpose: This was a phase II study designed to assess the safety of 3D-Conformal partial breast irradiation for local recurrence of breast carcinoma ≤ 3 cm in greatest dimension on pathologic specimen and ≤ 3 positive lymph nodes without extracapsular extension documented after evaluation. Detectable CTC incidence was unknown in patients (pts) with local recurrence only. CTCs were assessed pre and post treatment (tx) to determine incidence in this cohort, and determine correlation with outcome if feasible.

Methods: CTCS were assessed using the Cellsearch kit and assay prior to and within 3 weeks after completing radiotherapy. Nine cases were shipped after the recommended timeline and were analyzed after > 72 hours. These data are included in the analysis. Outcome endpoints included IBR and distant metastases-free survival [DMFS; with or without IBR]. All analyses are descriptive. Due to small numbers, only frequencies of outcomes are reported.

Results: Forty-seven (81%) pts consented to participate in CTC analysis. The median follow-up for consenting pts was 3.66 years (min-max: 2.25 to 5.02 years). Variables were balanced between consenting and non-consenting pts. Thirty-one pts (66%) had paired pre and post-tx samples. Eight pts (17%) had detectable CTCs pre-tx; 32 (68%) were undetectable; and 7 (15%) were not evaluated. Eight pts (17%) had detectable CTCs post-tx; 26 (55%) were undetectable; and 13 (28%) were not evaluated. At both time points the majority of detectable CTC cases were found to have 1 CTC (5/8 pre, 6/8 post). In DCIS cases with CTC consent, 4/19 had pre-tx detectable CTCs and 3/14 had post-tx detectable CTCs. Among pts with both a pre and post-tx CTC result, 8 pts had a change in CTCs: 3 pts (10%) had detectable CTCs pre-tx and undetectable post-tx and 5 pts (16%) had undetectable CTCs pre-tx and detectable post-tx. Four of these were in pts with DCIS. Of those not consenting, there were 2 DMFS events and no IBR events. Two consenting pts had IBRs and 2 additional pts had DMFS. One IBR pt had undetectable pre and post-tx CTCs and one had undetectable CTCs pre-tx and detectable post-tx. One DMFS pt had detectable CTCs pre and post-tx while the other pt was not evaluated.

Conclusions: Considering consent and processing, a high proportion of paired samples were obtained. Incidence of detectable pre-tx CTCs is modestly lower than historical reports from cohorts with distant metastases. Low event rates preclude conclusions regarding association with outcome. Supported by NCI grants: U10CA180868, U10CA180822, UG1CA189867, U24CA180803

Citation Format: Wendy A. Woodward, Kathryn A. Winter, Douglas W. Arthur, Bruce G. Haffty, Henry M. Kuerer, Anthony Lucci, Summer Jackson, Eric A. Strom, Kathleen Beekman, Wayne H. Pinover, Frank G. Basile, Christine M. Fisher, Reshma Jagsi, Elin R. Sigurdson, Julia R. White. Circulating tumor cell (CTC) analysis in NRG oncology/RTOG 1014, repeat breast conserving treatment after in-breast recurrence (IBR) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-240. doi:10.1158/1538-7445.AM2017-LB-240