Plexiform neurofibromas are congenital peripheral nerve sheath tumors characteristic of neurofibromatosis type 1 (NF1)—a frequent neurocutaneous disorder caused by mutations of the NF1 tumor suppressor gene. Since plexiform neurofibromas are a major cause of the burden of disease and may also progress to malignancy, many efforts have been undertaken to find a cure for these tumors. However, neither surgery nor medication has so far produced a breakthrough therapeutic success. Recently, a clinical phase I study reported significant shrinkage of plexiform neurofibromas following treatment with the MEK inhibitor selumetinib. Here, we report an 11-year-old NF1 patient with a large plexiform neurofibroma of the neck that had led to a sharp-angled kinking of the cervical spine and subsequent myelopathy. Although surgical stabilization of the cervical vertebral column was urgently recommended, the vertebral column was inaccessible due to extensive tumor growth. In this situation, treatment with the MEK inhibitor trametinib was initiated which resulted in a 22% reduction in tumor volume after 6 months of therapy and finally enabled surgery. These data show that MEK inhibitors may not lead to complete disappearance of NF1-associated plexiform neurofibromas but can be an essential step in a multimodal therapeutic approach for these tumors. The course of our patient suggests that MEK inhibitors are likely to play a significant role in providing a cure for one of the most devastating manifestations of NF1.

Neurofibromatosis type-1 (NF1)-associated plexiform neurofibromas (PN) are peripheral nerve sheath tumors that can significantly affect the quality of life. Until recently, surgery was the only treatment for these tumors. However, in most cases, surgery cannot achieve complete tumor removal and carries a high risk of postoperative deficits. Therefore, the recent approval of the MEK inhibitor selumetinib for the treatment of NF1-associated PN provides a long-awaited novel therapeutic option. Here, we report our experience with MEK inhibitor treatment in 12 pediatric NF1 patients with inoperable symptomatic PN. Eight patients received trametinib (median therapy duration 12.13 months and range 4–29 months), and four patients received selumetinib (median therapy duration 6.25 months and range 4–11 months). Volumetric magnetic resonance imaging (MRI) after 6 months of treatment was available for seven trametinib patients (median tumor volume reduction of 26.5% and range 11.3–55.7%) and two selumetinib patients (21.3% tumor volume reduction in one patient and +3% tumor volume change in the other one). All patients reported clinical benefits such as improved range of motion or reduced disfigurement. Therapy-related adverse events occurred in 58.3% of patients and mainly consisted of skin toxicity, paronychia, and gastrointestinal symptoms. Two patients discontinued trametinib treatment after 14 and 29 months when severe skin toxicity occurred and no further reduction of tumor size was observed. In one patient, discontinuation of therapy resulted in a 27.2% tumor volume increase as demonstrated on volumetric MRI 6 months later. Our data show that MEK inhibition is a novel therapeutic approach for inoperable PN with promising results and a manageable safety profile.

Diagnosis of neurofibromatosis type 1 (NF1) can be established when at least two out of seven defined clinical findings are present. However, a definite clinical diagnosis may be challenging, especially in young children. Therefore, we tried to identify additional clinical signs suggestive of NF1. We observed that nevi anemici (NA) occur with increased frequency in NF1 patients. To establish NA as an additional diagnostic criterion for NF1 we evaluated their exact frequency in children potentially affected by NF1. During a 6-month period we examined 100 NF1 patients and documented patients' age and sex as well as presence, location, and characteristic features of NA. We were able to show that NA are present in 28% of NF1 patients, which is well above the 5% prevalence of NA in the general population. It is not known why NA appear with increased frequency in NF1. We hypothesize that an imbalance between α- and β-adrenergic receptors, resulting in increased α-adrenergic vasoconstriction might be the underlying cause of NF1-associated NA. Based on our own observations and previously published studies, we propose that NA in children with suspected NF1 might facilitate definite diagnosis and improve clinical management.

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