De-intensification of postoperative radiotherapy in head and neck cancer irrespective of human papillomavirus status-results of a prospective multicenter phase II trial (DIREKHT Trial).

Background: Current standard treatment concepts in head and neck squamous cell carcinoma (HNSCC) are based on former studies using 2D and 3D treatment plans. However, modern radiation techniques allow for a more precise and individual dose application. Therefore, in a clearly defined patient population, de-intensified risk-adapted radiation is investigated. Methods: Patients with newly diagnosed HNSCC after surgery (with resection margins ≥1 mm and cM0) with the following tumor stages (TNM 7th Edition) were eligible for the study: oral cavity, oropharynx, or larynx: pT1-3, pN0-pN2b; hypopharynx: pT1-2, pN1. The patients should have either a low risk of local recurrence [≤pT2, resection margin ≥5 mm, no peritumoral lymphangiosis (L0), and no perineural invasion] or contralateral lymph node metastasis (≤3 ipsilateral lymph node metastases, in case of well-lateralized oropharyngeal or oral cavity cancer contralateral cN0, otherwise pN0). Patients were assigned to three different treatment regimes with reduction of the treated volume, radiation dose, or both, according to tumor stage and results of surgery performed. The primary objective was to show an LRR of <10% after 2 years. Findings: A total of 150 patients were enrolled. Tumor localizations were as follows: n = 53 (35.3%), oral cavity; n = 94 (62.7%), oropharynx (82% HPV-positive); n = 2 (1.3%), hypopharynx; and n = 1 (0.7%), larynx. A total of 61 patients (41.0%) were stage IVA, 81 (54.0%) were stage III, and 8 (5.3%) were stage II. Median follow-up was 36 months. Cumulative incidence of 2y-LRR was 5.6% (95% CI: 1.7%-9.2%) in the whole study population and 14.1% (95% CI: 3.8%-23.2%) in patients with oral cavity cancer. Cumulative incidence of 2y-LRR in non-irradiated or dose-reduced regions was 3.5% (95% CI: 0.4%-6.5%). After 2 years, disease-free survival was 92% (95% CI: 87%-96%) and overall survival was 94% (95% CI: 90%-98%) for the complete study cohort. Acute III° toxicity was as follows: dysphagia, 30%; xerostomia, 7%; mucositis, 19%; and dermatitis, 4%. Dysphagia and xerostomia decrease over time. After 27 months, late dysphagia III° and xerostomia II° were 1% and 9%, respectively. Interpretation: The study met its primary objective. De-intensification of postoperative radiotherapy irrespective of HPV status in a predefined patient population is associated with a favorable toxicity profile without compromising LRR. In an unplanned subgroup analysis, a significantly increased risk of LRR was observed in patients with oral cavity cancer. In these patients, de-intensified radiotherapy should be applied with caution.

Guidelines: onkopedia - what´s new? Locally advanced rectal cancer.

This article briefly summarizes clinically relevant new aspects of the recently published German, Austrian and Swiss onkopedia guideline for the treatment of locally advanced rectal cancer. Main aspects comprise (i) the use of total neoadjuvant therapy (TNT) for rectal cancers with high risk features, (ii) treatment with neoadjuvant chemotherapy for patient with a low risk for local recurrence, (iii) immunotherapy using dostarlimab in patients with MSI high /dMMR rectal cancer as well as (iv) intended organ preservation as a treatment goal. The availability of several evidence-based treatment options requires intensive discussion within the multidisciplinary team as well as dedicated information for patients about treatment goals, options and risks of individual treatment approaches.

Persistent Lymph Node Metastases After Neoadjuvant Chemoradiotherapy for Rectal Cancer.

Importance: Patients with locally advanced rectal cancer and persistent lymph node metastases (PLNM) after neoadjuvant treatment are at high risk of developing locoregional and distant metastasis, yet optimal postsurgical treatment of these patients is limited. Objective: To analyze the association of PLNM with pretreatment clinical parameters, intensity of neoadjuvant treatment, and long-term oncological outcomes. Design, Setting, and Participants: This cohort study is a post-hoc analysis of 3 randomized clinical trials (Surgical Oncology Working Group of Germany [CAO], Radiological Oncology Working Group of Germany [ARO], and Working Group for Internal Oncology in the German Cancer Society [AIO]) conducted in Germany in 1994, 2004, and 2012 that included 1948 patients with locally advanced rectal cancer recruited between February 1995 and January 2018. Statistical analysis was conducted between September 2023 and February 2024. Exposures: Receiving preoperative fluorouracil-based chemoradiotherapy (CRT, comprising the preoperative group of CAO/ARO/AIO-94 and the control group of CAO/ARO/AIO-04), fluorouracil-based CRT plus oxaliplatin (experimental group of CAO/ARO/AIO-04), or total neoadjuvant treatment (TNT) with fluorouracil-based CRT plus oxaliplatin with induction or consolidation leucovorin calcium (folinic acid), fluorouracil, and oxaliplatin chemotherapy within the CAO/ARO/AIO-12 trial. Main Outcome and Measures: The associations of PLNM with clinical parameters, intensity of neoadjuvant treatment, and cumulative incidences of LR, DM, and overall survival were assessed. Results: A total of 1888 patients (1333 male participants [70.6%]; median [range] age, 62 [19-84] years) with locally advanced rectal adenocarcinoma (clinical tumor stage 3 to 4 and/or clinically node-positive) treated within 3 consecutive clinical trials were analyzed. A total of 522 (29%) experienced PLNM; 378 had lymph node stage (ypN) 1 (20%) after neoadjuvant treatment (ypN) 1 (20%), and 174 had ypN2 (9%). Age, clinical T-stage, N-stage, grading, carcinoembryonic antigen levels, and time interval from completion of CRT to surgery were significantly associated with PLNM, whereas sex and tumor location were not. The percentage of patients with ypN2 stage was almost halved after TNT (18 of 293 patients [6%]) compared with patients treated with fluorouracil-based CRT (114 of 1009 patients [11.3%]; χ26 = 16.693; P = .01). After a median (IQR) follow-up of 54 (37-62) months, 5-year overall survival was 86.1% (95% CI, 83.9%-88.4%) for ypN0, 74.0% (95% CI, 83.9%-88.4%) for ypN1, and 43% for ypN2 (95% CI, 35.4%-52.2%) (P < .001). The 5-year cumulative incidences of locoregional and distant metastases were, respectively, 3% (95% CI, 2.1%-4.2%) and 20% (95% CI, 18%-23%) for ypN0, 6% (95% CI, 3.4%-8.8%) and 40% (95% CI, 34%-46%) for ypN1, and 19% (95% CI, 13%-26%) and 72% (95% CI, 63%-79%) for ypN2 (both P < .001). Conclusions and Relevance: In this cohort study, PLNM unmasked an unfavorable phenotype of rectal cancer at high risk for treatment failure. More aggressive adjuvant treatment might be considered; however, risk-adapted surveillance strategies and early recurrence-directed surgery, if feasible, are important strategies in this group of patients with CRT- and/or chemotherapy-resistant disease.

Chemoradiotherapy plus induction or consolidation chemotherapy as total neoadjuvant therapy for locally advanced rectal cancer: Pooled analysis of the CAO/ARO/AIO-12 and the OPRA randomized phase 2 trials.

BACKGROUND: Total neoadjuvant therapy (TNT) has been used for patients with locally advanced rectal cancer. The optimal sequence of chemoradiotherapy (CRT) and chemotherapy (CT) is a matter of debate. METHODS: We performed a pooled analysis of the CAO/ARO/AIO-12 and OPRA multicenter, randomized phase 2 trials to identify patient subsets that could benefit from one TNT sequence over the other regarding disease-free survival (DFS). Patients with stage II/III rectal cancer were randomized to CRT (50.4-54 Gy) with either induction (INCT-CRT) or consolidation CT (CRT-CNCT) with fluorouracil, leucovorin, oxaliplatin (CAO/ARO/AIO-12 and OPRA) or capecitabine and oxaliplatin (OPRA) followed by mandatory total mesorectal excision (TME) (CAO/ARO/AIO-12) or selective watch-and-wait surveillance (OPRA). 311 and 324 patients were recruited from June 15, 2015 to January 31, 2018; and from April 12, 2014 to March 30, 2020 in the two trials, respectively. Pretreatment clinical and tumor characteristics included were age, sex, ECOG, cT-category, cN-category, clinical UICC stage, location from anal verge, and tumor grade. FINDINGS: In total, 628 eligible patients were included in the pooled analysis (CAO/ARO/AIO-12, n = 304; OPRA, n = 324). Of those, 313 were randomly assigned to the INCT-CRT group, and 315 to the CRT-CNCT group. Median follow-up was 43 months (IQR, 35-49) months in the CAO/ARO/AIO-12 trial and 61,2 months (IQR, 42-68,4) in the OPRA trial. Pooled analysis of baseline clinical and tumor characteristics did not identify any subgroups of patients that would benefit by the one TNT sequence over the other with regard to DFS. INTERPRETATION: To our knowledge, this is the first pooled analysis of two randomized trials after direct head-to-head comparison of both TNT sequences. Both trials reported higher rates of complete response with CRT-CNCT, and this should be considered the preferred TNT sequence if organ preservation is a priority.

Future direction of total neoadjuvant therapy for locally advanced rectal cancer.

Despite therapeutic advancements, disease-free survival and overall survival of patients with locally advanced rectal cancer have not improved in most trials as a result of distant metastases. For treatment decision-making, both long-term oncologic outcomes and impact on quality-of-life indices should be considered (for example, bowel function). Total neoadjuvant therapy (TNT), comprised of chemotherapy and radiotherapy or chemoradiotherapy, is now a standard treatment approach in patients with features of high-risk disease to prevent local recurrence and distant metastases. In selected patients who have a clinical complete response, subsequent surgery might be avoided through non-operative management, but patients who do not respond to TNT have a poor prognosis. Refined molecular characterization might help to predict which patients would benefit from TNT and non-operative management. Specifically, integrated analysis of spatiotemporal multi-omics using artificial intelligence and machine learning is promising. Three prospective trials of TNT and non-operative management in Japan, the USA and Germany are collaborating to better understand drivers of response to TNT. Here, we address the future direction for TNT.

Differences in the Course of CD4 and CD8 Cells After Chemoradiotherapy in People Living with HIV with Anal Cancer.

Incidence of anal carcinoma (AC) in people living with HIV (PLWH) is increased compared to the general population. Adverse effects of chemoradiotherapy (CRT) on the immune system are associated with a significant detrimental prognosis on overall survival in patients receiving CRT for solid tumors. The aim of this study was to evaluate immunological factors, in particular the differences in recovery of CD4+ and CD8+ cell counts before and after CRT for AC in PLWH. Retrospective single-center chart review extraction to analyze immunological data collected from PLWH with AC; descriptive statistics were used. Thirty-six PLWH with histologically proven AC were included in the analysis. Absolute CD4 cell count 60 months after CRT was 67.2% of the value at the beginning of CRT, whereas the CD8 cell count reached 82.3%. These differences were statistically significant (p = .048), whereas CD4/CD8-ratio remained stable. The findings of the presented study regarding CD4+ and CD8+ cell recovery after CRT are congruent with results from prior studies in non-HIV infected patients. Although not reaching the level of prior CRT T cell numbers, the ability to generate CD8+ cells seems to be better recovered, while CD4+ regeneration is more impaired. These observations are best explained by faster recovery of CD8+ cells via thymic-independent pathways, which are not available for regeneration of CD4+ cells. Further studies with larger numbers of patients are required to analyze the specific CD4+ and CD8+ cell subsets.

Early Efficacy End Points in Neoadjuvant Rectal Cancer Trials: Surrogacy Revisited.

Trial-level surrogacy is critical before early response endpoints are used to approve new therapies.

Stereotactic body radiotherapy with volumetric intensity-modulated arc therapy and flattening filter-free beams: dosimetric considerations.

PURPOSE: The present study comparatively evaluates the impact of energy-matched flattening filter-free (FFF) photon beams with different energy levels on the physical-dosimetric quality of lung and liver stereotactic body radiotherapy (SBRT) treatment plans. METHODS: For this purpose, 54 different lung and liver lesions from 44 patients who had already received SBRT combined with volumetric modulated arc therapy (VMAT) were included in this retrospective planning study. Planning computed tomography scans already available were used for the renewed planning with 6 MV, 6 MV-FFF, 10 MV, and 10 MV-FFF under constant planning objectives. The treatment delivery data, dosimetric distributions, and dose-volume histograms as well as parameters such as the conformity index and gradient indices were the basis for the evaluation and comparison of treatment plans. RESULTS: A significant reduction of beam-on time (BOT) was achieved due to the high dose rates of FFF beams. In addition, we showed that for FFF beams compared to flattened beams of the same energy level, smaller planning target volumes (PTV) require fewer monitor units (MU) than larger PTVs. An equal to slightly superior target volume coverage and sparing of healthy tissue as well as organs at risk in both lung and liver lesions were found. Significant differences were seen mainly in the medium to lower dose range. CONCLUSION: We found that FFF beams together with VMAT represent an excellent combination for SBRT of lung or liver lesions with shortest BOT for 10 MV-FFF but significant dose savings for 6 MV-FFF in lung lesions.

The value of subcutaneous xenografts for individualised radiotherapy in HNSCC: Robust gene signature correlates with radiotherapy outcome in patients and xenografts.

PURPOSE: To assess the robustness of prognostic biomarkers and molecular tumour subtypes developed for patients with head and neck squamous cell carcinoma (HNSCC) on cell-line derived HNSCC xenograft models, and to develop a novel biomarker signature by combining xenograft and patient datasets. MATERIALS AND METHODS: Mice bearing xenografts (n = 59) of ten HNSCC cell lines and a retrospective, multicentre patient cohort (n = 242) of the German Cancer Consortium-Radiation Oncology Group (DKTK-ROG) were included. All patients received postoperative radiochemotherapy (PORT-C). Gene expression analysis was conducted using GeneChip Human Transcriptome Arrays. Xenografts were stratified based on their molecular subtypes and previously established gene classifiers. The dose to control 50 % of tumours (TCD50) was compared between these groups. Using differential gene expression analyses combining xenograft and patient data, a gene signature was developed to define risk groups for the primary endpoint loco-regional control (LRC). RESULTS: Tumours of mesenchymal subtype were characterized by a higher TCD50 (xenografts, p < 0.001) and lower LRC (patients, p < 0.001) compared to the other subtypes. Similar to previously published patient data, hypoxia- and radioresistance-related gene signatures were associated with high TCD50 values. A 2-gene signature (FN1, SERPINE1) was developed that was prognostic for TCD50 (xenografts, p < 0.001) and for patient outcome in independent validation (LRC: p = 0.007). CONCLUSION: Genetic prognosticators of outcome for patients after PORT-C and subcutaneous xenografts after primary clinically relevant irradiation show similarity. The identified robust 2-gene signature may help to guide patient stratification, after prospective validation. Thus, xenografts remain a valuable resource for translational research towards the development of individualized radiotherapy.

Prevalence and implications of significance testing for baseline covariate imbalance in randomised cancer clinical trials: The Table 1 Fallacy.

BACKGROUND: The 'Table 1 Fallacy' refers to the unsound use of significance testing for comparing the distributions of baseline variables between randomised groups to draw erroneous conclusions about balance or imbalance. We performed a cross-sectional study of the Table 1 Fallacy in phase III oncology trials. METHODS: From ClinicalTrials.gov, 1877 randomised trials were screened. Multivariable logistic regressions evaluated predictors of the Table 1 Fallacy. RESULTS: A total of 765 randomised controlled trials involving 553,405 patients were analysed. The Table 1 Fallacy was observed in 25% of trials (188 of 765), with 3% of comparisons deemed significant (59 of 2353), approximating the typical 5% type I error assertion probability. Application of trial-level multiplicity corrections reduced the rate of significant findings to 0.3% (six of 2345 tests). Factors associated with lower odds of the Table 1 Fallacy included industry sponsorship (adjusted odds ratio [aOR] 0.29, 95% confidence interval [CI] 0.18-0.47; multiplicity-corrected P < 0.0001), larger trial size (≥795 versus <280 patients; aOR 0.32, 95% CI 0.19-0.53; multiplicity-corrected P = 0.0008), and publication in a European versus American journal (aOR 0.06, 95% CI 0.03-0.13; multiplicity-corrected P < 0.0001). CONCLUSIONS: This study highlights the persistence of the Table 1 Fallacy in contemporary oncology randomised controlled trials, with one of every four trials testing for baseline differences after randomisation. Significance testing is a suboptimal method for identifying unsound randomisation procedures and may encourage misleading inferences. Journal-level enforcement is a possible strategy to help mitigate this fallacy.

Overall Survival After Treatment Failure Among Patients With Rectal Cancer.

Importance: Oncologic outcomes among patients with rectal cancer after developing local recurrence and/or distant metastases remain poorly studied. Objective: To analyze the trend of overall survival after treatment failure for patients with rectal cancer within three consecutive phase 2 or 3 trials of the German Rectal Cancer Study Group. Design, Setting, and Participants: This cohort study is a post hoc analysis of 3 randomized phase 2 or 3 trials (CAO/ARO/AIO-94, -04, and -12 trials, conducted in Germany) that included 1948 patients with locally advanced rectal adenocarcinoma. The CAO/ARO/AIO-94 trial recruited patients between February 1995 and September 2002, the CAO/ARO/AIO-04 trial recruited patients between July 2006 and February 2010, and the CAO/ARO/AIO-12 trial recruited patients between June 2015 and January 2018. Statistical analysis was conducted between September 2022 and March 2023. Exposures: A total of 119 of 391 patients in the CAO/ARO/AIO-94 trial group A, 295 of 1236 patients in the CAO/ARO/AIO-04 trial, and 69 of 306 in the CAO/ARO/AIO-12 trial experienced treatment failure (R2 resection or local recurrence or distant metastases) and were included in further analyses. Main Outcomes and Measures: Characteristics of treatment failure and overall survival were assessed in all 3 trial cohorts. Results: Of the 1948 patients treated in the 3 trials, 15 were excluded because of missing data. Of the remaining 1933 patients (median age, 62.5 years [range, 19-84 years]; 1363 men [71%] and 570 women [29%]) with locally advanced rectal adenocarcinoma (cT3 or 4 or cN+) treated within 3 consecutive clinical trials, 483 experienced treatment failure and were analyzed. After a median follow-up of 36 months (IQR, 24-51 months) for all patients, overall survival after treatment failure was significantly improved in the CAO/ARO/AIO-04 trial (at 3 years, 44% [IQR, 37%-51%]; hazard ratio [HR], 0.61 [95% CI, 0.47-0.79]) and further improved in the CAO/ARO/AIO-12 trial (at 3 years, 73% [IQR, 60%-87%]; HR, 0.32 [95% CI, 0.18-0.54]) compared with the CAO/ARO/AIO-94 trial (at 3 years, 30% [IQR, 22%-39%]) (both P < .001). Distant metastasis was the main reason for treatment failure throughout a 5-year follow-up (range, 67%-87%), and the relative risk for treatment failure was highest in the first 18 months in all 3 trials. ypTNM stage was significantly associated with the risk and time interval to treatment failure. Improvement in overall survival after treatment failure was independent of sex. Conclusions and Relevance: This cohort study suggests that advancements in salvage strategies during the past decades have likely improved overall survival among patients with rectal cancer who experienced treatment failure.

Real-world evidence of outcomes of oligometastatic hormone-sensitive prostate cancer patients treated with metastasis-directed therapy.

OBJECTIVE: To investigate characteristics and outcomes of oligometastatic hormone-sensitive prostate cancer (mHSPC) patients undergoing metastases-directed therapy (MDT) with external beam radiation therapy (EBRT). MATERIALS AND METHODS: We relied on an institutional tertiary-care database to identify mHSPC patients who underwent EBRT as MDT between 12/2019 and 12/2022. Main outcomes consisted of progression to metastatic castration-resistant prostate cancer (mCRPC) and overall mortality (OM). Oligometastatic was defined as ≤3 metastases and bone and/or lymph node deposits were treated with conventional doses up to 54 Gy or with hypofractionated stereotactic regimes of median 24 Gy (20-27 Gy). RESULTS: Overall, 37 patients treated with EBRT as MDT were identified. The median follow-up was 13 months. Median age at MDT was 71 years and 84% exhibited ECOG performance status 0. The median baseline PSA at diagnosis was 10 ng/mL. Overall, primary local therapy consisted of radical prostatectomy (65%), followed by external beam radiation therapy to the prostate (11%), focal therapy (8%), and palliative transurethral resection of the prostate (5%). Overall, 32% exhibited de novo oligometastatic mHSPC. Bone metastases were present in 78% versus 19% lymph node metastases versus 3% both. The distribution of targeted oligo-metastases was 62% versus 38% for respectively one metastasis versus more than one metastasis. Androgen deprivation therapy (ADT) was combined with MDT in 84%. Moreover, 19% received combination therapy with apalutamide/enzalutamide and 12% with abiraterone or docetaxel. The median time to mCRPC was 50 months. In incidence analyses, 13% developed mCRPC after 24 months. OM after 24 months was 15% in mHSPC patients receiving MDT. Significant OM differences were observed after stratification into targeted metastatic burden (<0.05). No high-grade adverse events were recorded during MDT. CONCLUSION: Our real-world data suggest that MDT represents a safe treatment option for well-selected oligometastatic mHSPC patients.

pCR and 2-Year Disease-Free Survival: A Combination of the Two Endpoints as a New Classification for Locally Advanced Rectal Cancer Patients-An Updated Pooled Analysis of Eleven International Randomized Trials.

LARC is managed by multimodal treatments whose intensity can be highly modulated. In this context, we need surrogate endpoints to help predict long-term outcomes and better personalize treatments. A previous study identified 2yDFS as a stronger predictor of OS than pCR in LARC patients undergoing neoadjuvant RT. The aim of this pooled analysis was to assess the role of pCR and 2yDFS as surrogate endpoints for OS in a larger cohort. The pooled and subgroup analyses were performed on large rectal cancer randomized trial cohorts who received long-course RT. Our analysis focused on the evaluation of OS in relation to the pCR and 2-year disease status. A total of 4600 patients were analyzed. Four groups were identified according to intermediate outcomes: 12% had both pCR and 2yDFS (the better); 67% achieved 2yDFS but not pCR (the good); 1% had pCR but not 2yDFS; and 20% had neither pCR nor 2yDFS (the bad). The pCR and 2yDFS were favorably associated with OS in the univariate analysis, and 2yDFS maintained a statistically significant association in the multivariate analysis independently of the pCR status. The combination of the pCR and 2yDFS results in a strong predictor of OS, whereas failure to achieve 2yDFS carries a poor prognosis regardless of the pCR status. This new stratification of LARC patients could help design predictive models where the combination of 2yDFS and pCR should be employed as the primary outcome.

DNA-Methylome-Based Tumor Hypoxia Classifier Identifies HPV-Negative Head and Neck Cancer Patients at Risk for Locoregional Recurrence after Primary Radiochemotherapy.

PURPOSE: Tumor hypoxia is a paradigmatic negative prognosticator of treatment resistance in head and neck squamous cell carcinoma (HNSCC). The lack of robust and reliable hypoxia classifiers limits the adaptation of stratified therapies. We hypothesized that the tumor DNA methylation landscape might indicate epigenetic reprogramming induced by chronic intratumoral hypoxia. EXPERIMENTAL DESIGN: A DNA-methylome-based tumor hypoxia classifier (Hypoxia-M) was trained in the TCGA (The Cancer Genome Atlas)-HNSCC cohort based on matched assignments using gene expression-based signatures of hypoxia (Hypoxia-GES). Hypoxia-M was validated in a multicenter DKTK-ROG trial consisting of human papillomavirus (HPV)-negative patients with HNSCC treated with primary radiochemotherapy (RCHT). RESULTS: Although hypoxia-GES failed to stratify patients in the DKTK-ROG, Hypoxia-M was independently prognostic for local recurrence (HR, 4.3; P = 0.001) and overall survival (HR, 2.34; P = 0.03) but not distant metastasis after RCHT in both cohorts. Hypoxia-M status was inversely associated with CD8 T-cell infiltration in both cohorts. Hypoxia-M was further prognostic in the TCGA-PanCancer cohort (HR, 1.83; P = 0.04), underscoring the breadth of this classifier for predicting tumor hypoxia status. CONCLUSIONS: Our findings highlight an unexplored avenue for DNA methylation-based classifiers as biomarkers of tumoral hypoxia for identifying high-risk features in patients with HNSCC tumors. See related commentary by Heft Neal and Brenner, p. 2954.

Robotic stereotactic body radiotherapy for localized prostate cancer: final analysis of the German HYPOSTAT trial.

PURPOSE: We report results of the first German prospective multicenter single-arm phase II trial (ARO 2013-06; NCT02635256) of hypofractionated robotic stereotactic body radiotherapy (SBRT) for patients with localized prostate cancer (HYPOSTAT). METHODS: Patients eligible for the HYPOSTAT study had localized prostate cancer (cT1­3 cN0 cM0), Gleason score ≤ 7, prostate-specific antigen (PSA) ≤ 15 ng/ml, prostate volume ≤ 80 cm3, and an International Prostate Symptom Score (IPSS) ≤ 12. Initially, inclusion was limited to patients ≥ 75 years or patients 70-74 years with additional risk factors. The trial protocol was later amended to allow for enrolment of patients aged ≥ 60 years. The treatment consisted of 35 Gy delivered in 5 fractions to the prostate and for intermediate- or high-risk patients, also to the proximal seminal vesicles using the CyberKnife system (Accuray Inc., Sunnyvale, CA, USA). Primary endpoint was the rate of treatment-related gastrointestinal or genitourinary grade ≥ 2 toxicity based on the RTOG scale 12-15 months after treatment. Secondary endpoints were acute toxicity, late toxicity, urinary function, quality of life, and PSA response. RESULTS: From July 2016 through December 2018, 85 eligible patients were enrolled and received treatment, of whom 83 could be evaluated regarding the primary endpoint. Patients mostly had intermediate-risk disease with a median PSA value of 7.97 ng/ml and Gleason score of 7a and 7b in 43.5% and 25.9% of patients, respectively. At the final follow-up 12-15 months after treatment, no patient suffered from treatment-related gastrointestinal or genitourinary grade ≥ 2 toxicity. Acute toxicity was mostly mild, with three grade 3 events, and the cumulative rate of grade ≥ 2 genitourinary toxicity was 8.4% (95% CI 4.1-16.4%). There were no major changes in urinary function or quality of life. The median PSA value dropped to 1.18 ng/ml 12-15 months after treatment. There was one patient who developed distant metastases. CONCLUSION: Robotic SBRT with 35 Gy in 5 fractions was associated with a favorable short-term toxicity profile. Recruitment for the HYPOSTAT­2 trial (ARO-2018­4; NCT03795337), which further analyses the late toxicity of this regimen with a planned sample size of 500 patients, is ongoing.