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Background: Sinonasal undifferentiated carcinoma (SNUC) is an extremely rare, high-grade, and aggressive tumor of the sinonasal tract. Due to the rarity of this malignancy, current treatment guidelines are based on small and often/mainly single-center retrospective datasets. In the absence of a universally accepted standard of care for SNUC, treatment approaches vary across countries and institutions, reflecting real-world clinical practice. The primary aim of this study was to describe real-world treatment and outcomes for patients with confirmed SNUC. Methods: This was an international, multi-center, retrospective, observational cohort study that pooled patients into the largest SNUC dataset to date. Fifteen centers were enrolled to contribute data, including seven from Europe, four from the United States, three from the United Kingdom, and one from Canada. In the absence of a universally accepted standard of care for SNUC, treatment approaches varied across countries and institutions, reflecting real-world clinical practice. Patients included were those with histologically confirmed SNUC who were treated between 1997 and 2021. Results: This study yielded 485 patients treated for SNUC. The median age at diagnosis was 55.6 years (IQR: 44.5–67.6), and 63.7% were male. Most cases presented at advanced stages, with 70.8% as T4a or T4b. Overall survival (OS) outcomes were available for 412 patients, with a median follow-up of 26.0 months. The 5- and 10-year OS were 47.2% (95% CI: 40.8–53.3%) and 39.6% (95% CI: 32.5–46.6%), respectively. Advanced age, dichotomized T-stage (T4a/b vs. T1–3), M-stage, and orbital involvement were significant poor prognostic factors on univariable analysis (p’s < 0.01). On multivariable analysis, orbital involvement (HR: 2.73, 95% CI: 1.42–5.27, p = 0.003) and distance metastasis stage (HR: 3.00, 95% CI: 1.25–7.21, p = 0.014) were both independently associated with worse OS. Conclusions: This observational study presents the largest multi-center cohort analysis of SNUC to date, providing new insights into prognostic factors for a rare cancer treated at global centers of excellence. Orbital involvement and the presence of metastases are candidate independent risk factors associated with poorer OS.

ABSTRACT Introduction Sinonasal sarcomas are exceedingly rare entities, constituting less than 7% of head and neck sarcomas. Their complex histology needs specialized treatment, which is often based on multimodal approaches including surgery, radiation therapy, and/or chemotherapy. This manuscript aims to gather expert opinions to establish common management principles for sinonasal sarcomas. Methods This international consensus followed a modified Delphi method in seven steps, including statements definition by the core group, expert panel recruitment, and a two‐round survey. Sixty‐two statements on sinonasal sarcoma management were developed. Experts from multiple continents participated, and results were anonymized and analyzed between March and May 2025. Results A total of 44 invited experts were recruited, 43.2% otorhinolaryngologists/head and neck surgeons, 31.8% medical oncologists, and 25% radiation oncologists. Participants varied in age and experience, representing Europe (70.5%), North America (18.2%), South America (6.8%), and Asia (4.5%). Among all histologies, biphenotypic sarcoma, chondrosarcoma, leiomyosarcoma, and myofibrosarcoma are principally treated with an upfront surgical management, differently from Ewing sarcoma and rhabdomyosarcoma in which chemotherapy, eventually associated with radiotherapy, is often chosen. In the remaining histologies (angiosarcoma, liposarcoma, malignant peripheral nerve sheath tumor [MPNST], osteosarcoma, and synovial sarcoma), a precise multimodal treatment is less standardized and needs to be discussed on a case‐by‐case basis. Conclusion Sinonasal sarcomas require a histology‐driven approach to determine upfront treatment, whether surgical, medical, or multimodal. Despite this structured strategy, prognosis remains highly variable across subtypes. Multidisciplinary evaluation and individualized management in referral centers are crucial to address the biological diversity and anatomical complexity of these rare malignancies.

e17019 Background: To report the role of combined chemotherapy in SGT. Methods: 251 patients with SGC treated in 2001-2011 were included in a collaborative IRB-approved retrospective RCN study. Chemotherapy is empirically administered based on extrapolation from conventional head and neck squamous cell carcinoma (Ca) (SCC) and data on systemic treatment in localized SGC are lacking. Results: Median age was 60 yo with 2/5 females/males. Tumor sites were the parotid 74.9%, submandibular 16%, sublingual 2.8% or minor gland 4%. Histologic findings were adenoid cystic (ACC) 17.3%, mucoepidermoid (MEC) 19.8%, adenoCa 15.6%, salivary duct (SDC) 10.3%, acinic cell (Aci) 6.2%, ex-pleomorphic 7.8%, undifferentiated 4.9%, myoepithelial 3.3%, epithelial myoepithelial 1.6%, basal cell 1.2%, lymphoepithelial 1.2%, others 4.0%. Surgery was performed in 95.1% (complete resection 38.1%). T stages 1, 2, 3 and 4 were 17.2%, 41.2%, 18.1% and 23.5% respectively. N stages were N0 61%, N1 13%, N2 24%, N3 2%. Perineural, vascular or lymphatic emboli were present in 47%, 24%, 27% respectively. Irradiation was performed postoperatively 96% or exclusively 4% (unilateral 84%, performed w/ photons only 78%, IMRT 41%). Chemotherapy was administered in 18%, dependent on grade, N stage, and emboli (p ≤ .05). None of 17 ex-pleomorphic, 25% of undifferentiated, 36% of SDC, and 66.7% of lymphoepithelial Ca received chemotherapy (p NS). With a median follow-up of 42 months for living patients, crude local, regional, metastatic relapse rates were 112% (in field 85%), 10%, 25%, respectively. Crude death rate was 28% including 77% from SGC. 5-year survival (5y OS) was 63%. The only prognostic factor was nodal involvement (p .002). However, 5y OS differed by histology: ACC 79%, MEC 84%, Aci 67%, SCC 43%, adenoCa NOS 40%, SDC 37%. Chemotherapy did not improve survival whatever histology. Conclusions: Further prospective studies are warranted to define the role of chemotherapy by histology in the setting of localized SGT. Also molecular profile-driven systemic treatments should be investigated.

(1) Background: To assess the role of postoperative external beam radiotherapy (pEBRT) on locoregional failure (LRF) for patients with locally advanced high-risk non-anaplastic thyroid carcinoma (naTC) at primary event or relapse. (2) Methods: Between 1995 and 2015, postoperative naTC patients with a theoretical indication for EBRT were included based on criteria that were common to American-British-French current guidelines, i.e., pT3-4, pN+, gross or microscopic residual disease. Inverse probability of treatment weighting (IPTW) after multiple imputation was used to reduce selection biases. (3) Results: Of 254 naTC patients, 216 patients underwent pEBRT (106 de novo, 110 at relapse, median dose 60 Gy) and 38 underwent surgery only. pEBRT patients had more gross residual disease, a major prognostic factor (p = 0.027) but less perineural invasion (p = 0.008) or lymphovascular emboli (p = 0.009). pEBRT patients more frequently underwent radioiodine therapy (p = 0.026). The 10-year cumulative incidence of LRF was 56% (95% CI, 32–74%) in operated patients, and 23% (95% CI, 17–30%) in pEBRT patients. After IPTW method, pEBRT reduced the risk of LRF (hazard ratio 0.30; 95% CI [0.18–0.49], p < 0.001), but had no impact on OS. In the pEBRT group, non-Intensity Modulated RadioTherapy (IMRT) plans and interruption of the radiotherapy were associated with poorer survival, while extended versus limited field strategy and dose were not. (4) Conclusions: In naTC patients who have pT3-4, pN+ disease or R1-2 resection, pEBRT improved LRF. Limited-field IMRT is preferred.

Abstract Background Paraganglioma of the head and neck (HNPGL) are rare often benign tumors. Surgery and radiation therapy (RT) are the main treatment choices. We present an analysis of outcome and toxicity after RT from 13 institutions of the Rare Cancer Network. Methods Data were collected using a questionnaire concerning patients' characteristics, treatment, and outcome. A total of 81 patients with 82 HNPGL were analyzed. Results The median follow‐up was 48 months (1‐456). Sixty‐two lesions were treated with conventional RT and 20 lesions with stereotactic RT. Local control (LC) was achieved in 69 out of 77 lesions. Late toxicity occurred in 17 patients. Patients treated with stereotactic RT experienced neither disease progression nor late toxicity. Four patients with a follow‐up longer than 20 years experienced disease progression. Conclusion RT for HNPGL offered good local control with acceptable toxicity. Stereotactic RT might offer better results. Long‐term follow‐up is required.

Primary hepatic lymphoma (PHL) is a rare malignancy. We aimed to assess the clinical profile, outcome and prognostic factors in PHL through the Rare Cancer Network (RCN). A retrospective analysis of 41 patients was performed. Median age was 62 years (range, 23-86 years) with a male-to-female ratio of 1.9:1.0. Abdominal pain or discomfort was the most common presenting symptom. Regarding B-symptoms, 19.5% of patients had fever, 17.1% weight loss, and 9.8% night sweats. The most common radiological presentation was multiple lesions. Liver function tests were elevated in 56.1% of patients. The most common histopathological diagnosis was diffuse large B-cell lymphoma (65.9%). Most of the patients received Chop-like (cyclophosphamide, doxorubicin, vincristine, and prednisone) regimens; 4 patients received radiotherapy (dose range, 30.6-40.0 Gy). Median survival was 163 months, and 5- and 10-year overall survival rates were 77 and 59%, respectively. The 5- and 10-year disease-free and lymphoma-specific survival rates were 69, 56, 87 and 70%, respectively. Multivariate analysis revealed that fever, weight loss, and normal hemoglobin level were the independent factors influencing the outcome. In this retrospective multicenter RCN study, patients with PHL had a relatively better prognosis than that reported elsewhere. Multicenter prospective studies are still warranted to establish treatment guidelines, outcome, and prognostic factors.

The Rare Cancer Network (RCN) was formed in the early 1990's to create a global network that could pool knowledge and resources in the studies of rare malignancies whose infrequency prevented both their study with prospective clinical trials. To date, the RCN has initiated 74 studies resulting in 46 peer reviewed publications. The First International Symposium of the Rare Cancer Network took place in Nice in March of 2014. Status updates and proposals for new studies were heard for fifteen topics. Ongoing studies continue for cardiac sarcomas, thyroid cancers, glomus tumors, and adult medulloblastomas. New proposals were presented at the symposium for primary hepatic lymphoma, solitary fibrous tumors, Rosai-Dorfman disease, tumors of the ampulla of Vater, salivary gland tumors, anorectal melanoma, midline nuclear protein in testes carcinoma, pulmonary lymphoepithelioma-like carcinoma, adenoid cystic carcinoma of the trachea, osteosarcomas of the mandible, and extra-cranial hemangiopericytoma. This manuscript presents the abstracts of those proposals and updates on ongoing studies, as well a brief summary of the vision and future of the RCN.

Approximately, twenty years ago, the Rare Cancer Network (RCN) was formed in Lausanne, Switzerland, to support the study of rare malignancies. The RCN has grown over the years and now includes 130 investigators from twenty-four nations on six continents. The network held its first international symposium in Nice, France, on March 21-22, 2014. The proceedings of that meeting are presented in two companion papers. This manuscript reviews the history of the growth of the RCN and contains the abstracts of fourteen oral presentations made at the meeting of prior RCN studies. From 1993 to 2014, 74 RCN studies have been initiated, of which 54 were completed, 10 are in progress or under analysis, and 9 were stopped due to poor accrual. Forty-four peer reviewed publications have been written on behalf of the RCN.

Kaposi's sarcoma (KS) most often affect the skin but occasionally affect the mucosa of different anatomic sites. The management of mucosal KS is seldom described in the literature. Data from 15 eligible patients with mucosal KS treated between 1994 and 2008 in five institutions within three countries of the Rare Cancer Network group were collected. The inclusion criteria were as follows: age >16 years, confirmed pathological diagnosis, mucosal stages I and II, and a minimum of 6 months’ follow-up after treatment. Head and neck sites were the most common (66%). Eleven cases were HIV-positive. CD4 counts correlated with disease stage. Twelve patients had biopsy only while three patients underwent local resection. Radiotherapy (RT) was delivered whatever their CD4 status was. Median total radiation dose was 16.2 Gy (0–45) delivered in median 17 days (0–40) with four patients receiving no RT. Six patients underwent chemotherapy and received from 1 to 11 cycles of various regimens namely vinblastin, caelyx, bleomycine, or interferon, whatever their CD4 counts was. Five-year disease free survival were 81.6% and 75.0% in patients undergoing RT or not, respectively. Median survival was 66.9 months. Radiation-induced toxicity was at worse grade 1–2 and was manageable whatever patients’ HIV status. This small series of mucosal KSs revealed that relatively low-dose RT is overall safe and efficient in HIV-positive and negative patients. Since there are distant relapses either in multicentric cutaneous or visceral forms in head and neck cases, the role of systemic treatments may be worth investigations in addition to RT of localized disease. Surgery may be used for symptomatic lesions, with caution given the risk of bleeding.