Infantile myofibromatosis: report on a family with autosomal dominant inheritance and variable penetrance

Pearls and Updates on Pediatric Tyrosine Kinase-Altered Tumors

Receptor tyrosine kinases (RTKs) are crucial cell surface receptors that activate intracellular signaling pathways in response to external stimuli, regulating cell proliferation and survival. Under normal conditions, RTK activity is tightly regulated. In pediatric tumors, particularly mesenchymal neoplasms, chromosomal rearrangements are the primary mechanism of RTK-driven oncogenesis, involving genes like NTRK1/2/3, ALK, ROS1, RET, EGFR, and PDGFRB. This review highlights recent advances in understanding RTK-driven myofibroblastic tumors, focusing on the molecular characteristics that influence their classification and clinical behavior. Integration of morphologic, immunophenotypic, and molecular information is essential for accurate diagnosis, given the complex overlap among these tumors.

Activating variants in PDGFRB result in a spectrum of disorders responsive to imatinib monotherapy

More than 50 individuals with activating variants in the receptor tyrosine kinase PDGFRB have been reported, separated based on clinical features into solitary myofibromas, infantile myofibromatosis, Penttinen syndrome with premature aging and osteopenia, Kosaki overgrowth syndrome, and fusiform aneurysms. Despite their descriptions as distinct clinical entities, review of previous reports demonstrates substantial phenotypic overlap. We present a case series of 12 patients with activating variants in PDGFRB and review of the literature. We describe five patients with PDGFRB activating variants whose clinical features overlap multiple diagnostic entities. Seven additional patients from a large family had variable expressivity and late-onset disease, including adult onset features and two individuals with sudden death. Three patients were treated with imatinib and had robust and rapid response, including the first two reported infants with multicentric myofibromas treated with imatinib monotherapy and one with a recurrent p.Val665Ala (Penttinen) variant. Along with previously reported individuals, our cohort suggests infants and young children had few abnormal features, while older individuals had multiple additional features, several of which appeared to worsen with advancing age. Our analysis supports a diagnostic entity of a spectrum disorders due to activating variants in PDGFRB. Differences in reported phenotypes can be dramatic and correlate with advancing age, genotype, and to mosaicism in some individuals.

Massive infantile myofibromatosis of the upper lip causing airway distress in a newborn

Infantile myofibromatosis is a rare condition characterized by benign spindle cell tumors most commonly involving the head, neck, and chest. An infant female with a prenatal diagnosis of a large facial mass was delivered via Cesarean at 34 weeks. Sparse prenatal care was received. Following delivery, the neonate was found to have an 8 cm ulcerative mass involving the upper lip and philtrum. Respiratory distress developed, and mask ventilation was difficult secondary to the size of the mass. The patient was successfully intubated after numerous attempts and then transferred to the children's hospital. Additional imaging demonstrated similar masses within bilateral iliopsoas and gluteal muscles, and her right gastrocnemius. A biopsy confirmed infantile myofibromatosis. At two weeks of life, she underwent resection with bilateral myocutaneous advancement flaps and successful extubation. She received adjuvant vinblastine and methotrexate for her pelvic and extremity disease with excellent response. We present the first case of airway distress secondary to myocutaneous myofibromatosis.

Myofibroma in Infancy and Childhood

Myofibromas are rare fibroblastic-myofibroblastic tumors in children. Their biological behavior is unpredictable and spontaneous regressions have been described. This is a retrospective review of clinical characteristics, treatment, and outcome of children diagnosed with myofibroma between 1999 and 2013 at Texas Children's Hospital. The median age at diagnosis of 42 patients was 37 months. Approximately two thirds of the patients were male. The median length of follow-up was 50.5 months (range, 0 to 165 mo). Thirty-eight patients (90%) had solitary lesions; 19 (50%) in the head and neck, 10 (26%) in the limbs, and 9 (24%) in the trunk. Twelve patients underwent a complete surgical resection. Of the 30 patients with positive margins, only 1 had tumor progression. Two patients had multicentric involvement, and 2 patients had generalized disease with visceral involvement. One patient with generalized disease and a progressive maxillary sinus mass was treated with vinblastine and methotrexate chemotherapy followed by complete surgical resection. All patients were alive at last follow-up. Myofibromas of childhood demonstrate clinical variability, and may spontaneously regress. Positive surgical margins do not adversely affect outcome. The rare patient with progressive unresectable disease may benefit from chemotherapy.

The spectrum of infantile myofibromatosis includes both non-penetrance and adult recurrence

Infantile myofibromatosis is characterized by benign myofibroblastic tumors within skin, muscle, bone or viscera which have a characteristic staining pattern on immunohistochemistry. The condition typically presents in infancy and the tumors often disappear by the third year of life. Mutations in the PDGFRB gene and NOTCH3 genes have been identified in familial forms of the condition. We present two families with molecularly confirmed germline mutations in the PDGFRB gene, one demonstrating a phenotype ranging from complete non-penetrance to neonatal lethality; and the other illustrating adult recurrence of the tumors.

Multiple Bone Lesions in an 8-Month-Old Child Presenting with Pathologic Fracture: A Rare Case of Solely Osseous Multicentric Infantile Myofibromatosis

CASE

An otherwise healthy 8-month-old boy presented with a pathologic fracture of the distal aspect of the radius. Further work-up demonstrated widespread osseous lesions of the axial and the appendicular skeleton with no soft-tissue or visceral involvement.

CONCLUSION

Infantile myofibromatosis has a spectrum of severity that demands a careful and complete work-up. In rare cases such as the present one, it can manifest as multiple osseous lesions. The patient in the present case was managed conservatively, with no morbidity demonstrated at 1 year of follow-up.

Vincristine and Dactinomycin in Infantile Myofibromatosis With a Review of Treatment Options

Although solitary presentations of infantile myofibromatosis tend toward spontaneous regression, multicentric forms fare worse. Previous case reports have depicted observation, surgical resection, and systemic therapies as treatment options. This paper reports well-tolerated, successful outcomes in a series of patients with high-risk infantile myofibromatosis in need of life-sustaining interventions treated with a combination of vincristine and dactinomycin. The clinical presentation, pathology, and radiographic findings are described.

Mutations in PDGFRB cause autosomal-dominant infantile myofibromatosis

Infantile myofibromatosis (IM) is a disorder of mesenchymal proliferation characterized by the development of nonmetastasizing tumors in the skin, muscle, bone, and viscera. Occurrence within families across multiple generations is suggestive of an autosomal-dominant (AD) inheritance pattern, but autosomal-recessive (AR) modes of inheritance have also been proposed. We performed whole-exome sequencing (WES) in members of nine unrelated families clinically diagnosed with AD IM to identify the genetic origin of the disorder. In eight of the families, we identified one of two disease-causing mutations, c.1978C>A (p.Pro660Thr) and c.1681C>T (p.Arg561Cys), in PDGFRB. Intriguingly, one family did not have either of these PDGFRB mutations but all affected individuals had a c.4556T>C (p.Leu1519Pro) mutation in NOTCH3. Our studies suggest that mutations in PDGFRB are a cause of IM and highlight NOTCH3 as a candidate gene. Further studies of the crosstalk between PDGFRB and NOTCH pathways may offer new opportunities to identify mutations in other genes that result in IM and is a necessary first step toward understanding the mechanisms of both tumor growth and regression and its targeted treatment.