Patients with rare cancers: Diagnosis and treatment patterns in the US.

235 Background: Rare cancers, defined as <6 cases per 100,000 people per year by the Surveillance of Rare Cancers in Europe and the Joint Action on Rare Cancers, are understudied in the US. This study describes the diagnosis and treatment patterns of rare cancers in the US using a nationwide cancer registry database to help uncover the unique challenges faced by patients with rare cancers. Methods: Patients of all ages who were diagnosed with first primary rare cancers between 01/2015 and 06/2022 across 50 US states and District of Columbia were identified from the National Cancer Database (NCDB). Rare cancers were extracted using the ICD-O-3 code of the SEER Rare Cancer Classification variable, which contained more than 200 rare cancers. We provided descriptive statistics to characterize patients with rare cancers, their diagnosis and treatment patterns, and timing of treatment initiation. Results: We identified 1,756,944 patients diagnosed with rare cancers in the US from 2015 to 2022, representing 23.4% of all cancer diagnoses during the study period. One-quarter of patients with rare cancers (25.6%) were aged ≤55 years old; 44.0% of patients were treated at academic facilities. The most common sites of rare cancers were the digestive system (34.8%), hematopoietic system (24.3%), head & neck (9.7%), and nervous system (7.6%); these sites represented about 10% of common cancers (Table). Notably, early-stage diagnoses were less common for rare than common cancers (32.5% vs. 60.1%) and 28.4% of rare cancer diagnoses (vs. 3.7% of common cancers) did not have applicable AJCC staging. Treatment patterns for patients with rare cancers varied by stage. Nearly one-quarter of patients with early-stage rare cancers (24.3%) did not receive any surgical treatment, over one-third of patients with stage IV (35.6%) did not receive systemic therapy, and only 20.8% of all patients received radiation therapy. Overall, 2.6% patients with rare cancers received treatment through clinical trials or other unconventional treatments. A total of 5.1%, 8.6% and 11.1% patients died within 30, 60, and 90 days of diagnosis, respectively. Among those who survived beyond these time points, 34.1%, 13.3%, and 6.0% had not received any treatment within 30, 60, and 90 days of diagnosis, respectively. Conclusions: Patients diagnosed with rare cancers present distinct diagnosis patterns and more than one-third did not initiate treatment within 30 days of diagnosis. Targeted efforts are warranted to improve access to care and health outcomes for patients diagnosed with rare cancers. Characteristics of patients newly diagnosed with rare and common cancers, NCDB 2015-2022. Rare (N=1,756,944) Common(N =5,766,999) % % System Head and neck 9.7 0.9 Digestive system 34.8 8.3 Nervous system 7.6 0.1 Hematopoietic system 24.3 0.0 All others 23.7 90.7 AJCC stage Early stage (I & II) 32.5 60.1 Late stage (III & IV) 32.0 31.1 Inapplicable 28.4 3.7 Unknown 7.2 5.1