Forward: Welcome to the Special Issue on Vascular Anomalies.

Welcome to the Special Issue on Vascular Anomalies It is timely and exciting that Pediatric Blood and Cancer has endorsed a supplement dedicated to vascular anomalies. Vascular anomalies are not new diseases. However, this generation of physicians is being newly exposed to the field due to revolutions in diagnostic imaging, genetic insights, and broadened roles of medical therapies. Many of our mentors have limited experience in vascular anomalies, which has restricted training opportunities. Historically, patients with rare diseases facing many unknowns are managed by these pioneers. In vascular anomalies, most patients were cared for by surgeons and interventional radiologists who could skillfully resect or debulk or inject these unusual vascular lesions. Over the past two decades, nomenclature has become standardized (https://www.issva.org/), genetic discoveries have informed classification and treatment decisions, and medical therapy has taken on a larger role in patient care. Many institutions now have dedicated clinicians working in an interdisciplinary “center” to provide comprehensive care to patients with vascular anomalies. Hematologists and oncologists are logical members of these teams, given our experience managing bleeding and thrombotic complications and utilizing antiproliferative and antiangiogenic therapies. As medical therapies now often target causative mutations or pathways active in many cancers, hematologist/oncologists are often leading care for these complex patients. Initiation of clinical trials and calls for evidence-based practices have positioned hematologists/oncologists as leaders in this field. Over a decade ago, a group of pediatric hematologists/oncologists working in this area recognized the growing need for providers in this specialty to care for patients with these conditions and promote research. From early discussions among providers came the idea for a collaborative group with an interest in vascular anomalies. The American Society of Pediatric Hematology/Oncology (ASPHO) introduced special interest groups (SIGs) in 2012 and in 2013, the ASPHO Vascular Anomaly Special Interest Group (ASPHO VA-SIG) was officially established, one of the original SIGs formed when this platform was first created. This group was founded by Dr. Denise Adams (while at Cincinnati Children's), Dr. Leo Brandao (Toronto Sick Kid's), and Dr. Cameron Trenor (Boston Children's), long-time collaborators with an interest in vascular anomalies. When the call for SIG applications was announced by ASPHO in summer 2012, this was a logical step for them to formalize the role of vascular anomalies in pediatric hematology-oncology. The primary mission of this group was to improve the care and outcomes for children and young adults with vascular anomalies through multicenter collaboration. The primary aims were education of fellow ASPHO members, establishing standards of practice, and developing collaborative research projects. At the first meeting in 2013 in Miami, the attendance was much higher than expected, and a community was born! The first Fall working meeting was held later that year in Cincinnati, and included patient advocates/support group leaders as well as clinicians. Working groups were formed to address identified needs in the areas of education, practice, and research. Since 2013, the VA-SIG has held a Spring meeting at ASPHO every year, and a Fall working meeting at a different host city each year. Even through the pandemic, we were able to participate virtually to come together to advance knowledge and practice of vascular anomalies. From the initial Fall meeting in Cincinnati with 34 attendees, we have developed a vibrant active community of 228 (as of February 26, 2022) ASPHO members that includes senior experts, interested trainees, advance practice providers, and patient support group partners. We organized educational primers before the ASPHO spring meetings in 2017 and 2021. We have presented multiple platform sessions at ASPHO national conferences, given several ASPHO webinars, and more recently partnered with the American Society of Hematology to spur interest and involve our adult colleagues in the care of our patients with vascular anomalies. The ASPHO VA-SIG is growing in membership and productivity. As part of more recent educational outreach, this supplement was an opportunity to provide guidance to our PHO colleagues and others with the interest and desire to help care for these complicated and rewarding patients. Many of the authors for this special issue are members of the VA-SIG and we are grateful for their contributions and for sharing their expertise. We are indebted to the pioneers who came before us, individual mentors at our institutions, and global mentors in this field, especially Drs. Judah Folkman and John Mulliken. We are driven by our patients and families and our thanks goes out to the patient support groups who support our momentum and drive for discovery.