Protocol digest of a randomized phase III trial comparing S-1-based chemoradiotherapy with/without nivolumab for unresectable locally advanced or borderline resectable pancreatic cancer: JCOG1908E (PENETRATE).

Pancreatic cancer remains a highly lethal disease with a 5-year survival proportion of <10%. Chemoradiotherapy is a treatment option for unresectable locally advanced (UR-LA) or borderline resectable (BR) pancreatic cancer, but its efficacy is not sufficient. Induction of the synergistic effect of irradiation and immune checkpoint inhibitors can be an attractive strategy. An open-label randomized phase III trial has been conducted since October 2020 to confirm the superiority of nivolumab plus S-1-based chemoradiotherapy over S-1-based chemoradiotherapy alone in patients with UR-LA or BR pancreatic cancer. A total of 216 patients will be enrolled in 14 institutions within 3.5 years. The primary endpoint of the safety run-in part is dose-limiting toxicity, and that of the phase III part is overall survival. This trial was registered at the Japan Registry of Clinical Trials as jRCT2080225361 (https://jrct.niph.go.jp/latest-detail/jRCT2080225361).

Acute adverse events of ultra-hypofractionated whole-breast irradiation after breast-conserving surgery for early breast cancer in Japan: an interim analysis of the multi-institutional phase II UPBEAT study.

BACKGROUND: The applicability of ultra-hypofractionated (ultra-HF) whole-breast irradiation (WBI) remains unknown in Japanese women. This study aimed to evaluate the safety and efficacy of this approach among Japanese women and report the results of an interim analysis performed to assess acute adverse events (AEs) and determine whether it was safe to continue this study. METHODS: We enrolled Japanese women with invasive breast cancer or ductal carcinoma in situ who had undergone breast-conserving surgery, were aged ≥ 40 years, had pathological stages of Tis-T3 N0-N1, and had negative surgical margins. Ultra-HF-WBI was delivered at 26 Gy in five fractions over one week. When the number of enrolled patients reached 28, patient registration was paused for three months. The endpoint of the interim analysis was the proportion of acute AEs of grade ≥ 2 (Common Terminology Criteria for Adverse Events v5.0) within three months. RESULTS: Of the 28 patients enrolled from seven institutes, 26 received ultra-HF-WBI, and 2 were excluded due to postoperative infections. No AEs of grade ≥ 3 occurred. One patient (4%) experienced grade 2 radiation dermatitis, and 18 (69%) had grade 1 radiation dermatitis. The other acute grade 1 AEs experienced were skin hyperpigmentation (n = 10, 38%); breast pain (n = 4, 15%); superficial soft tissue fibrosis (n = 3, 12%); and fatigue (n = 1, 4%). No other acute AEs of grade ≥ 2 were detected. CONCLUSIONS: Acute AEs following ultra-HF-WBI were within acceptable limits among Japanese women, indicating that the continuation of the study was appropriate.

The Japanese breast cancer society clinical practice guidelines for radiation treatment of breast cancer, 2022 edition.

The Breast Cancer Clinical Practice Guidelines, organized by the Japanese Breast Cancer Society (JBCS), were published in 2022. We present the English version of the Radiation Therapy (RT) section of the guidelines. The JBCS formed a task force to update the 2018 version of the JBCS Clinical Practice Guidelines. The Background Questions (BQs) contain the standard treatments for breast cancer in clinical practice, whereas the Clinical Questions (CQs) address daily clinical questions that remain controversial. Future Research Questions (FRQs) explore the subjects that are considered important issues, despite there being insufficient data for inclusion as CQs. The task force selected the 12 BQs, 8 CQs, and 6 FRQs for the RT section. For each CQ, systematic literature reviews and meta-analyses were conducted according to the Minds Manual for Guideline Development 2020, version 3.0. The recommendations, strength of recommendation, and strength of evidence for each CQ were determined based on systematic reviews and meta-analyses, and finalized by voting at the recommendation decision meeting.

The Japanese Breast Cancer Society Clinical Practice Guidelines for Breast Cancer, 2022 Edition: changes from the 2018 edition and general statements on breast cancer treatment.

The Japanese Breast Cancer Society Clinical Practice Guidelines for Breast Cancer, 2022 Edition was published in June 2022. The guidelines were prepared while conforming as much as possible to the "Minds Manual for Guideline Development 2020 ver. 3.0." edited by the Minds Manual Development Committee of the Japan Council for Quality Health Care in 2021. In addition, a survey of Japanese Breast Cancer Society members on the 2018 edition of the guidelines was conducted from February 19 to March 4, 2021. Based on the responses from over 600 members, original innovations were made to make the guidelines more user-friendly. The 2018 edition of the guidelines was developed to provide support tools for physicians and patients to utilize shared decision-making. The 2022 guidelines consist of two volumes: (1) an "Epidemiology and Diagnosis" section covering "Screening and Diagnosis", "Radiological diagnosis", and "Pathological diagnosis", and (2) a "Treatment" section covering "Surgical therapy", "Radiation therapy", and "Systemic therapy". We believe that this concise summary of the guidelines will be useful to physicians and researchers in Japan and overseas.

Population-based asymmetric margins for moving targets in real-time tumor tracking.

BACKGROUND: Both geometric and dosimetric components are commonly considered when determining the margin for planning target volume (PTV). As dose distribution is shaped by controlling beam aperture in peripheral dose prescription and dose-escalated simultaneously integrated boost techniques, adjusting the margin by incorporating the variable dosimetric component into the PTV margin is inappropriate; therefore, geometric components should be accurately estimated for margin calculations. PURPOSE: We introduced an asymmetric margin-calculation theory using the guide to the expression of uncertainty in measurement (GUM) and intra-fractional motion. The margins in fiducial marker-based real-time tumor tracking (RTTT) for lung, liver, and pancreatic cancers were calculated and were then evaluated using Monte Carlo (MC) simulations. METHODS: A total of 74 705, 73 235, and 164 968 sets of intra- and inter-fractional positional data were analyzed for 48 lung, 48 liver, and 25 pancreatic cancer patients, respectively, in RTTT clinical trials. The 2.5th and 97.5th percentiles of the positional error were considered representative values of each fraction of the disease site. The population-based statistics of the probability distributions of these representative positional errors (PD-RPEs) were calculated in six directions. A margin covering 95% of the population was calculated using the proposed formula. The content rate in which the clinical target volume (CTV) was included in the PTV was calculated through MC simulations using the PD-RPEs. RESULTS: The margins required for RTTT were at most 6.2, 4.6, and 3.9 mm for lung, liver, and pancreatic cancer, respectively. MC simulations revealed that the median content rates using the proposed margins satisfied 95% for lung and liver cancers and 93% for pancreatic cancer, closer to the expected rates than the margins according to van Herk's formula. CONCLUSIONS: Our proposed formula based on the GUM and motion probability distributions (MPD) accurately calculated the practical margin size for fiducial marker-based RTTT. This was verified through MC simulations.

Long-term outcomes of stimulated salivary flow and xerostomia after definitive intensity-modulated radiation therapy for patients with head and neck cancer†.

This retrospective study aimed to evaluate the time to recovery from xerostomia and analyze its predictors, along with long-term outcomes of stimulated salivary flow after intensity-modulated radiation therapy (IMRT) for head and neck cancer (HNC). We evaluated patients with HNC who had received IMRT with curative intent between 2012 and 2018 at our institution. The salivary recovery ratio (SRR) was defined as '(the stimulated salivary flow)/(pre-treatment salivary flow)'. The cutoff value of SRR in salivary recovery was estimated via the relationship between SRR and xerostomia grades. The salivary recovery time was defined as the time for SRR to exceed cutoff values from the end of radiotherapy. Fifty-seven patients were analyzed, with a 48-month median follow-up period of stimulated salivary flow. The cutoff value for SRR was 44.8%, and patients with a higher grade of xerostomia had a lower SRR (P < 0.001). The median salivary recovery time was 12 months. The cumulative incidence rates of salivary recovery at two and four years were 84 (95% confidence interval [CI]: 53-79) and 92% (95% CI: 82-97), respectively, and these were significantly lower in patients with a higher mean parotid gland dose, mean oral cavity dose and stimulated salivary flow per parotid gland volume. Stimulated salivary flow and xerostomia recover over a long period after radiotherapy.

Safety and efficacy of neoadjuvant chemoradiotherapy with moderately hypofractionated intensity-modulated radiotherapy for resectable pancreatic cancer: A prospective, open-label, phase II study.

BACKGROUND: Resectable pancreatic cancer (RPC) is potentially resectable on admission, and the impact of neoadjuvant therapy on these tumors is controversial. Moreover, the safety and efficacy of neoadjuvant chemoradiotherapy with moderately hypofractionated intensity-modulated radiation therapy (NACIMRT) for RPC have not been studied. Here, we conducted a phase II study to evaluate the safety and efficacy of hypofractionated NACIMRT for RPC. METHODS: A total of 54 RPC patients were enrolled and treated according to the study protocol. We used moderately hypofractionated (45 Gy in 15 fractions) IMRT with gemcitabine to shorten the duration of radiotherapy and reduce gastrointestinal toxicity. The primary endpoint was overall survival (OS), and we subsequently analyzed the microscopically margin-negative resection (R0) rate, disease-free survival (DFS), and histologic effects and safety of NACIMRT. RESULTS: Median OS for the cohort was 40.0 months. Forty-two patients (77.8%) underwent pancreatectomy after NACIMRT. Median DFS was 20.3 months. The R0 resection rate was 95.2% (40/42) per protocol and 85.2% (46/54) for the cohort. There were no intervention-related deaths during the study period. Local treatment response, as assessed by the CAP classification, showed no residual tumor in 4.8% of patients. Overall, 23.9% of patients experienced CTCAE grade 3 or 4 during NACIMRT. Adjuvant therapy was initiated in 88% of patients undergoing resection. Postoperative complications grade ≥3b on the Clavien-Dindo scale occurred in 4.8% of patients. CA19-9 level at enrollment was an independent prognostic factor for OS and DFS. CONCLUSIONS: This is the first prospective study of hypofractionated IMRT as neoadjuvant therapy for RPC. Hypofractionated NACIMRT for RPC could be safely introduced with a high induction rate of adjuvant chemotherapy, with an overall survival of 40.0 months.

New patient setup procedure using surface-guided imaging to reduce body touch and skin marks in whole-breast irradiation during the COVID-19 pandemic.

This study aimed to assess the effectiveness of a new patient-setup procedure using surface-guided imaging during the coronavirus disease 2019 (COVID-19) pandemic for left-sided whole-breast irradiation with deep inspiration breath-hold. Two setup procedures were compared regarding patient positioning accuracy for the first 22 patients. The first was a traditional setup (T-setup) procedure that used a surface-guided system after patient setup with traditional skin marks and lasers. The second procedure involved a new setup (N-setup) that used only a surface-guided system. The positioning accuracy of the remaining 23 patients was assessed using a setup that combined marker reduction and the N-setup procedure. No significant difference was observed in positioning accuracy between the two setups. The positioning accuracy of the marker-reduction setup was within 3 mm in all directions. The N-setup procedure may be a useful strategy for preventing infection during or after the COVID-19 pandemic.

Assessing target localization accuracy across different soft-tissue matching protocols using end-exhalation breath-hold cone-beam computed tomography in patients with pancreatic cancer.

The purpose of this study was to retrospectively assess target localization accuracy across different soft-tissue matching protocols using cone-beam computed tomography (CBCT) in a large sample of patients with pancreatic cancer and to estimate the optimal margin size for each protocol. Fifty-four consecutive patients with pancreatic cancer who underwent 15-fraction volumetric modulated arc therapy under the end-exhalation breath-hold condition were enrolled. Two soft-tissue matching protocols were used according to the resectability classification, including gross tumor volume (GTV) matching for potentially resectable tumors and planning target volume (PTV) matching for borderline resectable or unresectable tumors. The tolerance of the target localization error in both matching protocols was set to 5 mm in any direction. The optimal margin size for each soft-tissue matching protocol was calculated from the systematic and random errors of the inter- and intrafraction positional variations using the van Herk formula. The inter- and intrafraction positional variations of PTV matching were smaller than those of GTV matching. The percentage of target localization errors exceeding 5 mm in the first CBCT scan of each fraction in the superior-inferior direction was 12.6 and 4.8% for GTV and PTV matching, respectively. The optimal margin sizes for GTV and PTV matching were 3.7 and 2.7, 5.4 and 4.1 and 3.9 and 3.0 mm in the anterior-posterior, superior-inferior and left-right directions, respectively. Target localization accuracy in PTV matching was higher than that in GTV matching. By setting the tolerance of the target localization error, treatment can be successful within the planned margin size.

Impact of planning organ at risk volume margins and matching method on late gastrointestinal toxicity in moderately hypofractionated IMRT for locally advanced pancreatic ductal adenocarcinoma.

BACKGROUND: This study examined the differences in late gastrointestinal (GI) toxicities in moderately hypofractionated intensity-modulated radiation therapy (IMRT) for locally advanced pancreatic ductal adenocarcinoma (LA-PDAC) by changing the planning organs at risk volume (PRV) margin and the target matching method and assessed the causes of adverse events. METHODS: We examined 37 patients with LA-PDAC who underwent moderately hypofractionated IMRT between 2016 and 2020 at our institution; 23 patients were treated with wide PRV margins and soft tissue matching (Protocol A) and 14 with narrow PRV margins and fiducial marker matching (Protocol B). The GI toxicities, local control (LC) rate, and overall survival (OS) were assessed for each protocol. The initially planned and daily doses to the gross tumor volume (GTV), stomach, and duodenum, reproduced from cone-beam computed tomography, were evaluated. RESULTS: The late GI toxicity rate of grades 3-4 was higher in Protocol B (42.9%) than in Protocol A (4.3%). Although the 2-year LC rates were significantly higher in Protocol B (90.0%) than in Protocol A (33.3%), no significant difference was observed in OS rates. In the initial plan, no deviations were found for the stomach and duodenum from the dose constraints in either protocol. In contrast, daily dose evaluation for the stomach to duodenal bulb revealed that the frequency of deviation of V3 Gy per session was 44.8% in Protocol B, which was significantly higher than the 24.3% in Protocol A. CONCLUSIONS: Reducing PRV margins with fiducial marker matching increased GI toxicities in exchange for improved LC. Daily dose analysis indicated the trade-off between the GTV dose coverage and the irradiated doses to the GI. This study showed that even with strict matching methods, the PRV margin could not be reduced safely because of GI inter-fractional error, which is expected to be resolved with online adaptive radiotherapy.

Association between homologous recombination gene variants and efficacy of oxaliplatin-based chemotherapy in advanced pancreatic cancer: prospective multicenter observational study.

Next-generation sequencing (NGS)-based gene profiling can identify patients with pancreatic cancer with homologous recombinant repair gene pathogenic variants (HRRv). Several retrospective studies have reported a positive association between HRRv and the efficacy of platinum-based chemotherapy. However, this association remains to be validated in a prospective study. This multicenter, prospective, observational study included patients with histologically confirmed unresectable or recurrent pancreatic cancer who required systemic chemotherapy. Patients who were oxaliplatin-naïve patients were eligible. The HRRv status was measured using a College of American Pathologists-accredited NGS panel. One-year overall survival rate (1yr-OS%) was calculated after initiation of oxaliplatin-based chemotherapy and was set as the primary endpoint. Forty patients were enrolled between August 2018 and March 2020. The NGS success rate was 95% (38/40). HRRv was detected in 11 patients (27.5%). Oxaliplatin-based chemotherapy was administered to 9 of 11 patients with HRRv (81.8%) and 15 of 29 patients with non-HRRv (51.7%). The 1yr-OS% after initiation of oxaliplatin-based chemotherapy was 44.4% [95% confidence interval (CI) 13.7-71.9] and 57.1% (95% CI 28.4-78.0) in HRRv-positive and -negative cohorts, respectively. These data suggested that HRRv status alone could not be a potential predictive marker of oxaliplatin-based chemotherapy in patients with advanced pancreatic cancer. These results were in line with the results of a recent phase II study reporting the limited efficacy of poly(adenosine diphosphate-ribose) polymerase inhibitor in patients with pancreatic cancer who harbored HRRv other than BRCA. Future studies investigating patients with biallelic HRRv in the first-line setting are warranted.Trial registration UMIN000033655.

Long-term survival outcomes and recurrence patterns of olfactory neuroblastoma: A 13-year experience at a single institution.

OBJECTIVES: Olfactory neuroblastoma (ONB), also known as esthesioneuroblastoma, is a rare malignant neoplasm of the nasal vault and anterior skull base. The results of treatment for ONB are relatively good; however, regional and distant metastases can develop several years after definitive treatment. This study aimed to validate the treatment modality of ONB for oncological outcomes, especially for regional recurrence. METHODS: We retrospectively reviewed the medical records of 22 patients diagnosed with ONB at Kyoto University Hospital between 2009 and 2020. Descriptive statistics were calculated, and Kaplan-Meier curves were used. RESULTS: The median follow-up time was 58.2 months. One (4.5%) patient was clinically node positive, (cN+) and the remaining 21 (95.5%) were clinically node negative (cN0) at presentation. Eighteen patients underwent an endoscopic endonasal approach (EEA) for primary resection, and the remaining four patients underwent a combined EEA and transcranial approach. Elective neck dissection was not performed for 21 patients with cN0 ONB, whereas unilateral neck dissection with removal of ipsilateral lateral retropharyngeal node was performed for one patient with cN+ ONB. Postoperative radiotherapy without concurrent chemotherapy was performed only at the primary tumor bed for 21 patients with cN0 ONB, and at the primary tumor bed and bilateral neck for one patient with cN+ ONB. The 5-year overall, disease-specific, and disease-free survival rates were 94.1%, 100%, and 69.6%, respectively. No patients developed local recurrence, but 6 (27.2%) patients experienced recurrence with a median time to recurrence of 36.4 months, including four and two patients who initially developed regional recurrences and bone metastases, respectively. Five (22.7%) patients had delayed neck recurrence. The salvage rate was only 60.0% in the five patients who had delayed neck recurrence. Regarding the level of delayed neck recurrence, 4 (18.2%) patients had lateral retropharyngeal lymph node metastases. CONCLUSION: Patients with ONB have excellent survival outcomes after endoscopic surgical resection of the primary lesion with postoperative radiotherapy only to the primary tumor bed. Despite excellent survival, delayed neck recurrence, including the lateral retropharyngeal lymph node, remains high. Because salvage surgery for lateral retropharyngeal lymph node recurrence is sometimes technically difficult, it may be better to extend the field of postoperative radiotherapy from the primary tumor bed only to include bilateral lateral retropharyngeal lymph node regions in patients with clinically N0 ONB. Further prospective studies with a large number of patients are needed to determine the extent of postoperative radiotherapy.

Continuous and Early Progression of Carotid Intima-Media Thickness after Radiotherapy for Head and Neck Cancer: 5-Year Prospective Observational Study.

INTRODUCTION: Radiation-induced carotid artery stenosis (RI-CS) is known as one of long-term side effects of radiotherapy for head and neck cancer (HNC). However, the clinical time course after irradiation has been poorly understood. We aimed to investigate the natural history of radiation-induced carotid atherosclerosis, comparing the patients who received radiotherapy for HNC with the patients who were treated without radiotherapy. METHODS: The patients who received treatment of HNC at Department of Otolaryngology, Head and Neck Surgery of Kyoto University Hospital, from November 2012 to July 2015 were enrolled. The patients were assigned into the RT group and the control group, depending on whether radiotherapy was planned or not. Annual carotid ultrasound was performed from the enrollment to 5 years. The increase of mean intima-media thickness (IMT) at common carotid artery from the enrollment (Δmean IMT) was evaluated. RESULTS: Fifty-six patients in the RT group and 25 patients in the control group were enrolled. From 5-year follow-up data, the significant higher increase of Δmean IMT was consistently observed in the RT group than in the control group after 2 years. The RT group presented a 7.8-fold increase of mean IMT compared to the control group (0.060 mm per year in the RT group and 0.008 mm per year in the control group). Cumulative incidence curves obtained from the analysis of all vessels revealed that the RT group presented higher incidence of Δmean IMT ≥0.25 mm than the control group (p < 0.01). In the RT group, the patients with mean IMT ≥1.0 mm at enrollment exhibited significantly higher incidence of Δmean IMT ≥0.25 mm than the patients with mean IMT <1.0 mm (p < 0.01). DISCUSSION: Radiotherapy for HNC induces continuous carotid mean IMT progression. The irradiated carotid arteries with mean IMT ≥1.0 mm before radiotherapy presented earlier IMT progression than those with mean IMT <1.0 mm.

The mutual relationship between the host immune system and radiotherapy: stimulating the action of immune cells by irradiation.

The effects of irradiation on tumor tissue and the host immune system are interrelated. The antitumor effect of irradiation is attenuated in the immunocompromised hosts. In addition, radiation alone positively and negatively influences the host immune system. The positive effects of radiation are summarized by the ability to help induce and enhance tumor-antigen-specific immune responses. The cancer-immunity cycle is a multistep framework that illustrates how the tumor-antigen-specific immune responses are induced and how the induced antigen-specific immune cells exert their functions in tumor tissues. Irradiation affects each step of this cancer-immunity cycle, primarily in a positive manner. In contrast, radiation also has negative effects on the immune system. The first is that irradiation has the possibility to kill irradiated effector immune cells. The second is that irradiation upregulates immunosuppressive molecules in the tumor microenvironment, whereas the third is that irradiation to the tumor condenses immunosuppressor cells in the tumor microenvironment. When used in conjunction with radiotherapy, immune checkpoint inhibitors can further leverage the positive effects of radiation on the immune system and compensate for the negative effects of irradiation, which supports the rationale for the combination of radiotherapy and immune checkpoint inhibitors. In this review, we summarize the preclinical evidence for the reciprocal effects of radiation exposure and the immune system, and up-front topics of the combination therapy of immune checkpoint inhibitors and radiotherapy.

Multi-institutional phase II study of ultra-hypofractionated whole-breast irradiation after breast-conserving surgery for breast cancer in Japan: Kyoto Radiation Oncology Study Group (UPBEAT study).

PURPOSE: The UK-FAST-Forward study showed that ultra-hypofractionated whole-breast irradiation (ultra-HF-WBI) involving five fractions of 26 Gy radiation over 1 week was not inferior to HF-WBI. However, it is not used in Japan due to safety concerns. In April 2022, we commenced a multi-institutional, single-arm, phase II trial. Our aim is to confirm the safety of ultra-HF-WBI after breast-conserving surgery (BCS) for breast cancer in Japanese women. METHOD: We plan to enroll 98 patients from 13 institutions. The primary endpoint is the proportion of late adverse events of grades ≥2 within 3 years. DISCUSSION: We believe that this highly promising clinical study can positively impact the Japanese guidelines for breast cancer treatment. The results will help us decide whether or not ultra-HF-WBI can be used as a more convenient alternative to WBI. REGISTRATION NUMBER AND DATE: This trial was registered in the UMIN Clinical Trials Registry (UMIN000047080) on March 4, 2022.

Potential utility of cone-beam CT-guided adaptive radiotherapy under end-exhalation breath-hold conditions for pancreatic cancer.

PURPOSE: The purpose of this study was to demonstrate the potential utility of cone-beam computed tomography (CBCT)-guided online adaptive radiotherapy (ART) under end-exhalation breath-hold (EE-BH) conditions for pancreatic cancer (PC). METHODS: Eleven PC patients who underwent 15-fraction volumetric-modulated arc therapy under EE-BH conditions were included. Planning CT images and daily 165 CBCT images were imported into a dedicated treatment planning system. The prescription dose was set to 48 Gy in 15 fractions. The reference plan was automatically generated along with predefined clinical goals. After segmentation was completed on CBCT images, two different plans were generated: One was an adapted (ADP) plan in which re-optimization was performed on the anatomy of the day, and the other was a scheduled (SCH) plan, which was the same as the reference plan. The dose distributions calculated using the synthetic CT created from both planning CT and CBCT were compared between the two plans. Independent calculation-based quality assurance was also performed for the ADP plans, with a gamma passing rate of 3%/3 mm. RESULTS: All clinical goals were successfully achieved during the reference plan generation. Of the 165 sessions, gross tumor volume D98% and clinical target volume D98% were higher in 100 (60.1%) and 122 (74.0%) ADP fractions. In each fraction, the V3 Gy  < 1 cm3 of the stomach and duodenum was violated in 47 (28.5%) and 48 (29.1%), respectively, of the SCH fractions, whereas no violations were observed in the ADP fractions. There were statistically significant differences in the dose-volume indices between the SCH and ADP fractions (p < 0.05). The gamma passing rates were above 95% in all ADP fractions. CONCLUSIONS: The CBCT-guided online ART under EE-BH conditions successfully reduced the dose to the stomach and duodenum while maintaining target coverage.

Phase Ib/II study of nivolumab combined with palliative radiation therapy for bone metastasis in patients with HER2-negative metastatic breast cancer.

Radiation therapy (RT) can enhance the abscopal effect of immune checkpoint blockade. This phase I/II study investigated the efficacy and safety of nivolumab plus RT in HER2-negative metastatic breast cancer requiring palliative RT for bone metastases. Cohort A included luminal-like disease, and cohort B included both luminal-like and triple-negative disease refractory to standard systemic therapy. Patients received 8 Gy single fraction RT for bone metastasis on day 0. Nivolumab was administered on day 1 for each 14-day cycle. In cohort A, endocrine therapy was administered. The primary endpoint was the objective response rate (ORR) of the unirradiated lesions. Cohorts A and B consisted of 18 and 10 patients, respectively. The ORR was 11% (90% CI 4-29%) in cohort A and 0% in cohort B. Disease control rates were 39% (90% CI 23-58%) and 0%. Median progression-free survival was 4.1 months (95% CI 2.1-6.1 months) and 2.0 months (95% CI 1.2-3.7 months). One patient in cohort B experienced a grade 3 adverse event. Palliative RT combined with nivolumab was safe and showed modest anti-tumor activity in cohort A. Further investigations to enhance the anti-tumor effect of endocrine therapy combined with RT plus immune checkpoint blockade are warranted.Trial registration number and date of registration UMIN: UMIN000026046, February 8, 2017; ClinicalTrials.gov: NCT03430479, February 13, 2018; Date of the first registration: June 22, 2017.