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BackgroundThe goal of this study was to assess the impact of trastuzumab on locoregional failure.METHODSThe analysis included 2763 patients with HER2‐positive (HER2+) breast cancer who were randomly assigned to adjuvant doxorubicin (A), cyclophosphamide (C), paclitaxel (T) and trastuzumab (H) (arm A, AC→T [n = 922]; arm B, AC→T→H [n = 988]; arm C, AC→T+H→H [n = 853]). Radiotherapy was given after AC→T concurrently with H. Radiotherapy was given after lumpectomy (L) or after mastectomy (M) with ≥4 positive lymph nodes but was optional for 1 to 3 positive lymph nodes. Locoregional failures at 10 years (LFR10) as first events were compared using competing risk analysis.ResultsThe median follow‐up was 13.0 years. The first site of failure was local‐only in 96 cases, locoregional in 16 cases, regional in 32 cases, and not specified in 2 cases; LFR10 was 4.8% (95% CI 4.1%‐5.7%). LFR10 was 5.5% (95% CI 4.3%‐7.2%), 4.9% (95% CI 3.7%‐6.4%), and 2.8% (95% CI 1.9%‐4.1%) in arms A, B, and C (B vs A: hazard ratio [HR] 0.91, P = .62; C vs A: HR 0.72, P = .12). For estrogen receptor–positive patients, LFR10 was 3.7% (95% CI 2.8%‐4.8%) and for estrogen receptor–negative patients, it was 6.1% (95% CI 5.0%‐7.4%; HR 0.61, P = .004). Local treatment included L+RT (n = 1044 [38%]), M+RT (n = 1025 [37%]), and M (n = 694 [25%]). LFR10 was 6.% (95% CI 5.0%‐7.8%), 3.0% (95% CI 2.1%‐4.3%), and 5.5% (95% CI 4.0%‐7.4%) for L+RT, M+RT, and M, respectively (M+RT vs L+RT: HR 0.43, P < .001; M vs L+RT: HR 0.88, P = .57). For 1 to 3 positive lymph nodes, LFR10 was 6.5% (95% CI 4.8%‐8.9%), 4.1% (95% CI 2.4%‐7.0%), and 4.3% (95% CI 2.9%‐6.5%) in L+RT, M+RT, and M, respectively (M vs L+RT: HR 0.68, P = .14; M vs M+RT: HR 1.2, P = .6).ConclusionLow 10‐year LFRs were seen regardless of trastuzumab use. Differences in local therapy in patients with 1 to 3 positive lymph nodes did not appear to improve local control. Local therapy studies for HER2+ and other tumor characteristics are important as the role of local therapies continues to evolve.

Abstract Background: Recent advances in radiotherapy techniques have allowed ablative doses to be safely delivered to inoperable liver tumors. In this setting, proton beam radiotherapy (PBT) provides the means to escalate radiation dose to the target volume while sparing the uninvolved liver. This study evaluated the safety and efficacy of hypofractionated PBT for liver tumors, predominantly hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (ICC).Methods: We evaluated the prospective registry of the Proton Collaborative Group for patients undergoing definitive PBT for liver tumors. Demographic, clinicopathologic, toxicity, and dosimetry information were compiled.Results: To date, 63 patients have been treated at 9 institutions between 2013-2019. Thirty (48%) had HCC and 25 (40%) had ICC. The median dose and biological equivalent dose (BED) delivered was 58.05 GyE (range, 32.5-75) and 80.5 GyE (range, 53.6-100), respectively. The median mean liver BED was 13.9 GyE. Three (4.8%) patients experienced at least one grade ³3 toxicity. With median follow-up of 5.1 months (range, 0.1-40.8), the local control (LC) rate at 1 year was 91.2% for HCC and 90.9% for ICC. The 1-year LC was significantly higher (95.7%) for patients receiving BED greater than 75.2 GyE than for patients receiving BED of 75.2 GyE or lower (84.6%, p = 0.029). The overall survival rate at 1 year was 65.6% for HCC and 81.8% for ICC. Conclusions: Hypofractionated PBT results in excellent LC, sparing of the uninvolved liver, and low toxicity, even in the setting of dose-escalation. Higher dose correlates with improved LC, highlighting the importance of PBT especially in patients with recurrent or bulky disease.

513 Background: The PCG registry is a multicenter registry for patients receiving proton therapy for various malignancies. The current abstract reviews the outcomes for patients receiving postoperative proton therapy for resected pancreatic cancer. Methods: From March, 2013 to August,2016 18 patients with resected pancreatic adenocarcinoma received postoperative proton therapy. The current study reviews the pretreatment characteristics and outcomes of these patients. Results: Median age -70 years (range 52 to 79); Males 12, Females 6; pT Stage -T2–4, T3–13, T4–1; N Stage -N1–12, N0–6; Margin Status -Close-8, Positive-4, Negative-6; Surgical approach -open-16, laparoscopic 2; Operations performed: standard pancreaticoduodenectomy-11, pylorus sparing pancreaticoduodenectomy-4, total pancreatectomy-1; Pancreaticoduodenectomy with portal vein reconstruction –1; Pancreaticoduodenectomy with irreversible electroporation. Median lymph nodes taken-16.50 (range 3 to 72); Median lymph nodes positive-1.5 (range 0 to 7); PNI positive-9, PNI negative-2, PNI unknown-4; LVI positive-7, LVI negative-6, LVI unknown-5; Median tumor size –3.1cm (range 2.2 to 6.2); Median dose delivered –50.51Gy(RBE) (range 27.88 to 54.00); Median treatment duration –38 calendar days (range 25 to 48); One patient died during treatment. One additional patient demonstrated grade 3 toxicity (anorexia, nausea, diarrhea). Only one patient’s treatment was protracted by more than 5 days. Median available follow up is 1.1 years (range 0.07 to 3.4 years); 2 year survival 37%. Conclusions: Postoperative proton therapy after pancreatectomy was well tolerated without treatment interruption or severe toxicity.

e16555 Background: The ProtecT trial underscores the importance of treatment in men with prostate cancer and life expectancies > 10 years and the validity of radiation therapy (RT). RT can be given with photons or protons (PT). To address the controversy of which is better, clinical outcomes of photon-based intensity modulated RT (IMRT) and PT cohorts from 2 institutions were directly compared. Methods: Under respective IRB approvals, data from 2 cohorts were analyzed. The first was 301 men treated with ultrasound image guided IMRT from 2000-05 to 75.6 Gy in 42 fractions. The second was 1214 men treated with fiducial image guided PT from 2006-10 to 78 CGE in 39 fractions. Median age and followup were 74 y and 7.2 y for IMRT and 66 y and 5.6 y for PT. Hormone therapy (ADT) was used with IMRT and PT, respectively, in 3% and 7% of low-risk patients, 25% and 9.9% of intermediate-risk, and 91% and 57.8% of high-risk. Comparative endpoints were age-stratified 5-year (5Y) survival (OS), ≥ grade 3 gastrointestinal (GI) and urologic (GU) toxicity, and 5Y freedom from biochemical progression (FFBP). Results: There was a lower prevalence of GI (1.3% vs 0.1%, p = 0.0065) and GU (4.3% vs 0.1%, p < 0.0001) toxicity at last follow-up in the PT group. In the IMRT and PT cohorts, OS rates were 90.8% and 88.7% in men ≥75 (p = 0.4083). In men < 75, OS rates were 91.6% and 97.5% in the IMRT and PT low-risk patients (p = 0.003), 92.1% and 95.5% in the IMRT and PT intermediate-risk (p = 0.0535), and 92.0% and 90.0% (p = 0.4975) in the IMRT and PT high-risk. In the IMRT and PT cohorts, respectively, FFBP rates were 92.2% and 98.9% for low-risk patients (p < 0.0001), 87.3% and 94.5% for intermediate-risk patients(p = 0.0226), and 80.3% and 74.4% for high-risk patients (p = 0.5154). Conclusions: In this retrospective comparison of outcomes in cohorts of men treated with IMRT and PT for prostate cancer, FFBP rates were better with PT for men with low- and intermediate-risk disease and similar in men with high-risk disease despite longer and more frequent use of ADT in the IMRT cohort. This study underscores the difficulty of comparing retrospective series, with differences noted in age, RT dose, and ADT use between cohorts. However, the magnitude of improvement with PT is intriguing and warrants prospective testing.