Clinical and Genetic Aspects of the Segmental Overgrowth Spectrum Due to Somatic Mutations in PIK3CA

Genetic basis and imaging findings of neurofibromatosis 1 and other somatic overgrowth disorders

Somatic overgrowth disorders comprise a wide range of rare conditions that present with focal enlargement of one or more tissue types. The PI3K-AKT-mTOR pathway is a signalling pathway that induces angiogenesis and cell proliferation, and is one of the most commonly overactivated signalling pathways in cancer. The PI3K-AKT-mTOR pathway can be up-regulated by genetic variants that code for proteins in this pathway, or down-regulated by proteins that inhibit the pathway. Mosaic genetic variations can result in cells that proliferate excessively in specific anatomical locations. The PIK3CA-related overgrowth spectrum (PROS) disorders include CLOVES syndrome, macrodystrophia lipomatosa, and Klippel-Trenaunay syndrome among many. The neurofibromatosis type 1 (NF1) gene encodes neurofibromin which down-regulates the PI3K-AKT-mTOR pathway. Thousands of pathological variants in the NF1 gene have been described which can result in lower-than-normal levels of neurofibromin and therefore up-regulation of the PI3K-AKT-mTOR pathway promoting cellular overgrowth. Somatic overgrowth is a rare presentation in NF1 with a wide range of clinical and radiological presentations. Hypertrophy of all ectodermal and mesodermal elements has been described in NF1 including bone, muscle, fat, nerve, lymphatics, arteries and veins, and skin. The shared signalling pathway for cellular overgrowth means that these radiological appearances can overlap with other conditions in the PIK3CA-related overgrowth spectrum. The aim of this review is to describe the genetic basis for the radiological features of NF1 and in particular compare the appearances of the somatic overgrowth disorders in NF1 with other conditions in the PIK3CA-related overgrowth spectrum.

Pediatric Vascular Anomalies: A Clinical and Radiological Perspective

According to the International Society for the Study of Vascular Anomalies (ISSVA) classification, vascular anomalies include a diverse range of pathologies, classified as either vascular tumors or vascular malformations. This classification, last revised in 2018, aims to explain the biological basis of vascular lesions and help clinicians to manage the anomalies. In vascular tumors, there are proliferative changes of endothelial cells, while vascular malformations primarily consist of structural vascular abnormalities. Infantile hemangioma is the most common soft-tissue vascular tumor. Vascular malformations are an extensive group of malformations of the arterial, venous, and lymphatic systems, either in isolation or in combination. Radiological evaluation plays a key part in the management of pediatric patients with these entities. The understanding of sonography and magnetic resonance imaging findings entails its correlation with clinical findings at the time of scanning.

How we approach complex vascular anomalies and overgrowth syndromes

Vascular anomalies, both vascular tumors and vascular malformations, can occur in isolation or as part of syndromes including those which feature phenotypic overgrowth. To update what is known about vascular anomalies associated with overgrowth, PubMed was searched for "overgrowth syndromes and vascular anomalies or malformations." PubMed, OMIM, and the Rare Disease Database also were searched for specific diagnoses. We review individual overgrowth syndromes, provide a case-based approach to the clinical, radiographic, pathologic, and genetic basis for diagnosis, to complications of both the vascular anomalies and the overgrowth, and emphasize the need for a multidisciplinary approach to care.

The Klippel-Trénaunay Syndrome in 2022: Unravelling Its Genetic and Molecular Profile and Its Link to the Limb Overgrowth Syndromes

The Klippel-Trénaunay syndrome is an unusual syndrome of vascular and dermatologic manifestation in which patients demonstrate hemihypertrophy of the soft tissue and bones of one limb, cutaneous haemangiomas and varicosities in anatomically abnormal positions. Described in 1900 by two French physicians, the etiology remained unclear until recently, when evidence emerged that there was a genetic basis for this sporadic disorder. Genes that encoded pathological angiogenic factors and caused vascular dysmorphogenesis, explaining the molecular bases of this syndrome, were identified. Several angiogenic genes were identified but one gene, the AGGF1 (formerly VG5Q) gene, was seen in mutations involving patients diagnosed with Klippel-Trénaunay syndrome. Furthermore, this syndrome was also noted to have overlapping clinical features linked with the “overgrowth syndromes,” in which genetic mutations along somatic lines were identified. These involved The PI3K enzyme which forms part of the phosphoinositide 3–kinase pathway which is encoded by the PIK3CA-gene. This enzyme mediates embryonic cellular growth in-utero and diseases involved in this pathway are classified as members of the PIK3CA-related overgrowth syndrome. This paper reviews the status of what is now known about the molecular genetics of this unusual, but clinically challenging disorder and its differentiation from similar diseases, linked with the PIK3CA-gene and the related overgrowth syndromes.

Update of pediatric soft tissue tumors with review of conventional MRI appearance-part 1: tumor-like lesions, adipocytic tumors, fibroblastic and myofibroblastic tumors, and perivascular tumors

There are numerous soft tissue tumors and tumor-like conditions in the pediatric population. Magnetic resonance imaging is the most useful modality for imaging these lesions. Although certain soft tissue lesions exhibit magnetic resonance features characteristic of a specific diagnosis, most lesions are indeterminate, and a biopsy is necessary for diagnosis. We provide a detailed update of soft tissue tumors and tumor-like conditions that occur in the pediatric population, emphasizing each lesion's conventional magnetic resonance imaging appearance, using the recently released 5th edition of the World Health Organization Classification of Soft Tissue and Bone Tumors as a guide. In part one of this review, pediatric tumor-like lesions, adipocytic tumors, fibroblastic and myofibroblastic tumors, and perivascular tumors are discussed. In part two, vascular lesions, fibrohistiocytic tumors, muscle tumors, peripheral nerve sheath tumors, tumors of uncertain differentiation, and undifferentiated small round cell sarcomas are reviewed. Per the convention of the WHO, these lesions involve the connective, subcutaneous, and other non-parenchymatous-organ soft tissues, as well as the peripheral and autonomic nervous system.

Vascular lesions of the pediatric orbit: A radiological walkthrough

Vascular anomalies of the pediatric orbit represent a heterogeneous group that include both vascular tumors and vascular malformations. The disorder may initially be silent and then associated with symptoms and/or function damage, depending on the type of vascular anomaly and its extension. Vascular tumors include benign, locally aggressive (or borderline) and malignant forms while vascular malformations are divided into "simple", "combined" and syndromic, or "low flow" or "high flow". Both entities can arise in isolation or as part of syndromes. In this review, we describe the imaging findings of the vascular lesions of the orbit in the pediatric population, which are key to obtain a correct diagnosis and to guide the appropriate treatment in the light of the new genetic and molecular discoveries, and the role of the radiologist in their multidisciplinary management. We will also touch upon the main syndromes associated with orbital vascular abnormalities.

Vascular anomalies of the head and neck: diagnosis and treatment

Vascular malformations and vascular tumors comprise the two specific subsets of vascular anomalies that arise as a result of disorganized angiogenesis and neoplasm, respectively. Malformations are separate entities from vascular tumors (e.g., hemangiomas) and are recognized by the International Society for the Study of Vascular Anomalies (ISSVA) as such. Vascular malformations are classified into four main groups: simple, combined, anomalies of major vessels, and those associated with other vascular anomalies. Vascular tumors are neoplastic growths of blood vessels and are morphologically and molecularly distinct from malformations but can arise in the head and neck and have syndromic association. Head and neck vascular anomalies are not uncommon in the pediatric population and require special care in the workup, diagnostic imaging and clinical care. The purpose of this manuscript is to discuss the diagnosis and management of the most common intracranial and extracranial vascular malformations and tumors in the head and neck in children and adolescents.

Custom Pediatric Oncology Next-Generation Sequencing Panel Identifies Somatic Mosaicism in Archival Tissue and Enhances Targeted Clinical Care

BACKGROUND

Disorders in the PIK3CA-related overgrowth spectrum because of somatic mosaicism are associated with segmental overgrowth of the body in conjunction with vascular, skeletal, and brain malformations such as hemimegalencephaly. A pathogenic variant may only be detectable in affected tissue and not in peripheral blood or saliva samples; therefore archival tissue may be the only relevant available specimen for testing. Although this is a common approach for cancer testing, it is not typically used for constitutional genetic disorders.

METHODS

PIK3CA mosaicism was assessed with a custom pediatric oncology next-generation sequencing panel (OncoKids) designed to capture somatic mutations in pediatric malignancies. The panel covers a wide range of targets including PIK3CA and AKT1 hotspots. We used OncoKids on archival formalin-fixed, paraffin-embedded or frozen samples from seven patients with facial hemihypertrophy and lipomas, hemimegalencephaly, or hemihypertrophy with a lymphovascular malformation. The age of the archival tissue examined by next-generation sequencing ranged from two to 13 years (median 5 years). Every patient had clinical manifestations within the PIK3CA-related overgrowth spectrum and had a sample of an affected tissue available for testing from a prior surgical intervention.

RESULTS

PIK3CA mosaicism was detected in all seven patients and the mutant allele fraction was lower in the lymphovascular malformation tissues (8% to 11%) than in brain (20% to 32%) and lipomatous (16% to 23%) tissues.

CONCLUSIONS

Our study highlights the clinical utility of using a robust, oncology-focused next-generation sequencing assay to identify PIK3CA mosaicism in noncancer cases. It is feasible to use archival samples that are more than a decade old to obtain a molecular diagnosis, which can then be used to improve health care management.

Vascular anomalies: special considerations in children

The diagnosis and treatment of vascular anomalies are a large part of the caseload for paediatric interventional radiologists. Although many of the principles of sclerotherapy and embolisation are the same in adult and paediatric practice, there are some key differences in the approach for children, including some longer term thinking about managing these chronic diseases and their impact on a growing child. Vascular tumours are not often seen in adult IR practice and the rarest can be life threatening; knowledge of the commonest types and the role IR can play in their management can be instrumental in ensuring that children get appropriate treatment in a timely manner. Vascular anomalies also encompass some conditions associated with complex overgrowth, a subject that often causes confusion and uncertainty for interventional radiologists. This paper presents a simplified and practical approach to this spectrum of disease.

Congenital infiltrating lipomatosis of the face with lingual mucosal neuromas associated with a PIK3CA mutation

We report the case of a 5-year-old girl with congenital right-sided facial hemihypertrophy and right hemi-macroglossia with lingual mucosal neuromas. The segmental presentation of findings suggested the diagnosis of congenital infiltrating lipomatosis of the face (CILF), which belongs within the PIK3CA-related overgrowth spectrum (PROS). This was confirmed by genetic analysis showing a mosaic mutation in PIK3CA H1047R. CILF/PROS should be considered in the differential diagnosis of mucosal neuromas.

Cerebellar dysplasia related to PIK3CA mutation: a three-case series

The term PROS (PIK3CA-Related Overgrowth Spectrum) indicates a wide spectrum of overgrowth disorders related to somatic mutations in PIK3CA (phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha) pathway. We present three cases with PIK3CA mutation and clinical characteristics encompassing MCAP (megalencephaly-capillary malformation) condition but lacking all criteria to a certain diagnosis, most of all showing prevalent and peculiar involvement of cerebellar structures at MRI (magnetic resonance imaging) mainly consisting in cortical rim thickening and abnormal orientation of folia axis. These cases expand the spectrum of intracranial MRI features in PIK3CA disorders.

PIK3CA vascular overgrowth syndromes: an update

PURPOSE OF REVIEW

Over the past decade many previously poorly understood vascular malformation disorders have been linked to somatic activating mutations in PIK3CA, which regulates cell survival and growth via activation of the mTOR1-AKT pathway. The goal of this article is to describe and provide an update on the clinical features, complications, and management strategies for the PIK3CA-related overgrowth spectrum (PROS).

RECENT FINDINGS

PROS encompasses a heterogenous group of disorders with complications related to the tissues harboring the mutation. Vascular malformation syndromes, such as Klippel-Trenaunay syndrome and Congenital Lipomatous Overgrowth Vascular malformations Epidermal nevi and Skeletal abnormalities, have an increased risk of thromboembolic complications, which is accentuated postprocedurally. Asymmetric overgrowth, particularly of limbs, results in a high rate of orthopedic complications. Hypoglycemia screening in the neonatal period and ongoing monitoring for growth failure is recommended in megalencephaly capillary malformation due to its association with multiple endocrinopathies. Recently, sirolimus, an mTOR1 inhibitor, has shown promise in vascular anomalies and now PROS. PIK3CA direct inhibitor, Alpelisib (BYL719), was recently trialed with significant clinical benefit.

SUMMARY

As the pathogenesis of these conditions is better elucidated and targeted treatments are developed, recognizing the clinical features, comorbidities, and evolving therapeutic landscape across the PROS spectrum becomes more crucial for optimization of care.

Congenital Limb Overgrowth Syndromes Associated with Vascular Anomalies

Congenital limb length discrepancy disorders are frequently associated with a variety of vascular anomalies and have unique genetic and phenotypic features. Many of these syndromes have been linked to sporadic somatic mosaicism involving mutations of the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) pathway, which has an important role in tissue growth and angiogenesis. Radiologists who are aware of congenital limb length discrepancies can make specific diagnoses based on imaging findings. Although genetic confirmation is necessary for a definitive diagnosis, the radiologist serves as a central figure in the identification and treatment of these disorders. The clinical presentations, diagnostic and imaging workups, and treatment options available for patients with Klippel-Trenaunay syndrome, CLOVES (congenital lipomatous overgrowth, vascular anomalies, epidermal nevi, and scoliosis/spinal deformities) syndrome, fibroadipose vascular anomaly, phosphatase and tensin homolog mutation spectrum, Parkes-Weber syndrome, and Proteus syndrome are reviewed. ^©RSNA, 2019.

Comprehensive molecular and clinicopathological analysis of vascular malformations: A study of 319 cases

Vascular malformations are part of overgrowth syndromes characterized by somatic mosaic mutations or rarely by germline mutations. Due to their similarities and diversity, clinicopathological classification can be challenging. A comprehensive targeted Next Generation Sequencing screen using Unique Molecular Identifiers with a technical sensitivity of 1% mutant alleles was performed for frequently mutated positions in ≥21 genes on 319 formalin‐fixed paraffin‐embedded samples. In 132 out of 319 cases pathogenic mosaic mutations were detected affecting genes previously linked to vascular malformations e.g. PIK3CA (n=80), TEK (TIE2) (n=11), AKT1 (n=1), GNAQ (n=7), GNA11 (n=4), IDH1 (n=3), KRAS (n=9), and NRAS (n=1). Six cases harbored a combination of mutations in PIK3CA and in GNA11 (n=2), GNAQ (n=2), or IDH1 (n=2). Aberrations in PTEN and RASA1 with a variant allele frequency approaching 50% suggestive of germline origin were identified in six out of 102 cases tested; four contained a potential second hit at a lower allele frequency. Ninety‐one of the total 142 pathogenic mutations were present at a variant allele frequency <10% illustrating the importance of sensitive molecular analysis. Clinicopathological characteristics showed a broad spectrum and overlap when correlated with molecular data. Sensitive screening of recurrently mutated genes in vascular malformations may help to confirm the diagnosis and reveals potential therapeutic options with a significant contribution of PIK3CA/mTOR and RAS‐MAPK pathway mutations. The co‐existence of two activating pathogenic mutations in parallel pathways illustrates potential treatment challenges and underlines the importance of multigene testing. Detected germline mutations have major clinical impact.

PIK3CA c.3140A>G mutation in a patient with suspected Proteus Syndrome: a case report

We present a patient with suspected Proteus Syndrome, an overgrowth disorder associated with AKT1c.49G>A mutation. NGS analysis detected PIK3CAc.3140A>G mutation in the patient's affected tissue allowing for PROS (PIK3CA-related overgrowth spectrum) diagnosis. The overlapping clinical features in overgrowth disorders highlight the importance of molecular testing for a correct diagnosis.

A case of congenital lipomatous overgrowth, vascular malformations, epidermal nevi, spinal/skeletal anomalies and/or scoliosis syndrome with lipoatrophy as an important clinical manifestation

Congenital lipomatous overgrowth, vascular malformations, epidermal nevi, spinal/skeletal anomalies and/or scoliosis syndrome is a PIK3CA-related overgrowth spectrum presenting with congenital, asymmetric, disproportionate overgrowth associated with dysregulated adipose tissue, enlarged bony structures, and mixed primarily truncal vascular malformations. We present this case to raise awareness that very thin body habitus (lipoatrophy) contrasting with areas of overgrowth can be an important clinical feature of this syndrome and, if not recognized, can lead to unnecessary investigations.

Therapeutic targeting of the angiopoietin-TIE pathway

The endothelial angiopoietin (ANG)-TIE growth factor receptor pathway regulates vascular permeability and pathological vascular remodelling during inflammation, tumour angiogenesis and metastasis. Drugs that target the ANG-TIE pathway are in clinical development for oncological and ophthalmological applications. The aim is to complement current vascular endothelial growth factor (VEGF)-based anti-angiogenic therapies in cancer, wet age-related macular degeneration and macular oedema. The unique function of the ANG-TIE pathway in vascular stabilization also renders this pathway an attractive target in sepsis, organ transplantation, atherosclerosis and vascular complications of diabetes. This Review covers key aspects of the function of the ANG-TIE pathway in vascular disease and describes the recent development of novel therapeutics that target this pathway.

An Extremely Rare Disorder of Somatic Mosaicism: CLOVES Syndrome

BACKGROUND

CLOVES (Congenital Lipomatous Overgrowth, Vascular malformations, Epidermal nevi Scoliosis, Skeletal, Spinal) syndrome is an extremely rare, complex, non-Mendelian genetic condition with clinical overlap to several other overgrowth syndromes.

PURPOSE

This article shares an interesting case report of the prenatal to postnatal diagnostic course for an infant with this condition.

CASE FINDINGS/RESULTS

It shares prenatal and postnatal images and imaging studies which helped confirm the diagnosis. In addition, the unusual genetic causes of the condition as well as recommended patient-specific management and treatment therapies for this complex condition are discussed.

IMPLICATIONS FOR PRACTICE

Practice implications include honing of physical examination skills and facilitating diagnostic testing required to differentiate CLOVES syndrome from similar conditions. Providers must provide ongoing information and ensure support to families during this diagnostic process. In addition, the majority of care will likely be provided beyond the newborn period. As such, providers must facilitate outpatient follow-up with a number of consultants after hospital discharge.

IMPLICATIONS FOR RESEARCH

Because CLOVES syndrome is so rare, research in this area is limited to a small number of field experts. These experts, however, are well-suited to continue research surrounding disease management and lesion treatment (whether surgical, procedural, or medical) moving forward.

Somatic PIK3CA mutations as a driver of sporadic venous malformations

Venous malformations (VM) are vascular malformations characterized by enlarged and distorted blood vessel channels. VM grow over time and cause substantial morbidity because of disfigurement, bleeding, and pain, representing a clinical challenge in the absence of effective treatments (Nguyenet al, 2014; Uebelhoeret al, 2012). Somatic mutations may act as drivers of these lesions, as suggested by the identification of TEK mutations in a proportion of VM (Limayeet al, 2009). We report that activating PIK3CA mutations gives rise to sporadic VM in mice, which closely resemble the histology of the human disease. Furthermore, we identified mutations in PIK3CA and related genes of the PI3K (phosphatidylinositol 3-kinase)/AKT pathway in about 30% of human VM that lack TEK alterations. PIK3CA mutations promote downstream signaling and proliferation in endothelial cells and impair normal vasculogenesis in embryonic development. We successfully treated VM in mouse models using pharmacological inhibitors of PI3Kα administered either systemically or topically. This study elucidates the etiology of a proportion of VM and proposes a therapeutic approach for this disease.