Abstract P2-13-05: Outcomes after accelerated partial breast irradiation in “high risk” and women categorized as cautionary in the ASTRO guidelines
Authors: Goulding Anabel , Leonard Charles , Tole Shannon , Barke Lora , Widner Jodi , Asmar Lina , Wang Yunfei 
Published: March 2020

Purpose: To report a primary objective clinical outcome of ipsilateral breast recurrence following accelerated partial breast irradiation (APBI) in cautionary (as described in 2017 revised ASTRO APBI guidelines) and high-risk women (age &lt;50, tumor size &lt;3 cm and ≥2 cm, HER2/neu positive, combined estrogen/progesterone (ER/PR) negative, ER negative, and triple negative). Secondary objectives of axillary and regional failure as well as overall survival are also reported.

Methods and Material: Between March 2004 and April 2016 patients were enrolled in two APBI breast protocols (Phase II NCT01185145 and Phase III NCT01185132). Patients were treated with 38.5 Gy IMRT or 3D-CRT APBI w/ 3.85 Gy fraction/BID fractionation for 10 fractions. Patients who were ER/PR negative, ER negative, PR negative, HER2 positive, ≥2 cm primary tumors, or triple negative were compared to a total of 543 patients who were enrolled in the Phase II and Phase III trials. High risk patients were defined as those who possess one or more high risk criteria: triple negative (n=30), ER-/PR- (n=40), tumor size ≥2 cm &lt;3 cm (n=50), HER 2+ (n=54), age range 40-50 years (n=120), ER- (n=43) and ILC histology (n=52). Clinical outcomes of ipsilateral breast, axillary, combined regional recurrences (breast or axillary) (RR), and overall survival (OS) were analyzed and compared in each cohort

Results: Median follow up was 4.0 years for all patients. No significant difference was found for this cautionary/high risk cohort at 5 years for ipsilateral breast, or regional recurrences. However, axillary recurrence was significantly adversely impacted by triple negative status, as well as both ER- and combined ER/PR- status (p=0.01, p=0.04, p=0.03, respectively). On multivariate analysis, the only significant correlations were between triple negative type and axillary recurrence (p=0.03). Overall survival for all patients was unaffected by any of the high-risk categories.

Estimated Recurrence-free and Overall Survival at 5 years

VariableIpsilateral breast recurrencepAxillary recurrencepRegional recurrencepAll Patients OSpHER-2/neupositive100%0.45100%0.64100%0.3895.3%0.88negative98%99.5%97.4%95.8%Size&lt;2 cm98%0.5699.5%0.6697.7%0.7795.9%0.11≥2 cm96%100%95.8%87.4%Both ER/PR negativeyes100%0.3297.3%0.0397.3%0.9886.6%0.25no98%99.7%97.6%95.9%

Triple negativeyes100%0.3496.7%0.0196.7%0.9384.3%0.16no98%99.7%97.6%95.9%HistologyIDCA98%0.4599.7%0.0797.7%0.7595.8%0.14ILCA100%97.5%97.5%88.9%Age&gt; 5098%0.2899.5%0.4597.8%0.5595.2%0.10≤ 5097%100%97%96.6%ERpositive97.9%0.399.7%0.0497.6%0.9496%0.29negative100%97.5%97.5%87.5%

Conclusion: There were no statistically significant differences in clinical local ipsilateral breast or regional recurrence outcomes at 5 years for patients currently considered to be cautionary/high risk. Axillary recurrence, however, was adversely impacted by triple negative, ER-, and combined negative ER/PR status. ER- and ER/PR- status similarly affected axillary recurrence. In light of these differences, however, the actual increase in axillary recurrence ranges from 2.4%-3% and are of questionable clinical significance. These data suggest that women possessing cautionary/high risk features are at no more risk for ipsilateral breast recurrence than other patients considered to be acceptable for APBI treatment.

Citation Format: Anabel Goulding, Charles Leonard, Shannon Tole, Lora Barke, Jodi Widner, Lina Asmar, Yunfei Wang. Outcomes after accelerated partial breast irradiation in “high risk” and women categorized as cautionary in the ASTRO guidelines [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-13-05.