January 9, 2017Oncology
Neurofibromatosis type 1 (NF1), also called von Recklinghausen’s disease, is a rare genetic disorder characterized by the development of multiple noncancerous (benign) tumors of nerves and skin (neurofibromas) and areas of abnormally decreased or increased coloration (hypo- or hyperpigmentation) of the skin. Areas of abnormal pigmentation typically include pale tan or light brown discolorations (cafe-au-lait spots) on the skin of the trunk and other regions as well as freckling, particularly under the arms (axillary) and in the groin (inguinal) area.
Such abnormalities of skin pigmentation are often evident by one year of age and tend to increase in size and number over time. At birth or early childhood, affected individuals may have relatively large benign tumors that consist of bundles of nerves (plexiform neurofibromas). Individuals with NF1 may also develop benign tumor-like nodules of the colored regions of the eyes (Lisch nodules) or tumors of the optic nerves (second cranial nerves), which transmit nerve impulses from the innermost, nerve-rich membrane of the eyes (retinas) to the brain. More rarely, affected individuals may develop certain malignant (cancerous) tumors. NF1 may also be characterized by unusual largeness of the head (macrocephaly) and relatively short stature. Additional abnormalities may also be present, such as episodes of uncontrolled electrical activity in the brain (seizures); learning disabilities; speech difficulties; abnormally increased activity (hyperactivity); and skeletal malformations, including progressive curvature of the spine (scoliosis), bowing of the lower legs, and improper development of certain bones. Plexiform neurofibromas develop in up to 50% of people with NF1. Complete surgical removal of the tumors is rarely feasible, and incompletely resected tumors tend to grow back.
The disease-causing gene for NF1 was first identified in 1990 by two independent teams, one of them led by NIH Director Francis S. Collins, Ph.D., M.D., who at the time was chief of Medical Genetics at the University of Michigan. The other team was led by Ray White at the University of Utah. Research to understand the gene’s function revealed that deregulation of the RAS signaling pathway was the most likely cause of tumor development. Numerous drugs that target RAS-related signaling pathways have been tested in patients with NF1 in phase I and phase II clinical trials, with disappointing results.
According to an article published online in the New England Journal of Medicine (29 Dec. 2016), in an early-phase clinical trial of a new oral drug, selumetinib, children with NF1 and plexiform neurofibromas, tumors of the peripheral nerves, tolerated selumetinib and, in most cases, responded to it with tumor shrinkage. NF1 affects 1 in 3,000 people.
The multicenter phase I clinical trial, which included 24 patients, and was conducted at the NIH Clinical Center and three participating sites. The primary aim of the clinical trial was to evaluate the toxicity and safety of selumetinib in patients with NF1 and inoperable plexiform neurofibromas, and, encouragingly, most of the selumetinib-related toxic effects were mild. At present, no therapies are considered effective for NF1-related large plexiform neurofibromas, but, in this trial, partial responses, meaning 20% or more reduction in tumor volume, were observed in over 70% of the patients. Responses were observed in tumors that were previously growing at a rate of greater than 20% per year, as well as in non-progressing lesions. Tumor shrinkage was maintained long term, for approximately two years, and, as of early 2016, no disease progression had been observed in any trial participant. Additionally, anecdotal evidence of clinical improvement, such as a decrease in tumor-related pain, improvement in motor function, and decreased disfigurement, was reported.
Selumetinib, provided for the study by AstraZeneca, is a selective inhibitor of the MEK protein, a part of the complex network of RAS signaling pathways. The drug has demonstrated activity in some advanced cancers, but it is not yet approved by the FDA. It is manufactured in capsule form to be taken orally.
Trial enrollment began in September 2011 and 24 children (11 girls, 13 boys) participated. Twice daily doses of the medicine were taken continuously, over a median of 30 month-long treatment cycles. The majority of patients are still continuing with therapy, some for as long as five years, and the long-term treatment has had no observed adverse effect on their development or overall health. In some patients, a loss of response to selumetinib with slow regrowth of tumors was observed, particularly after dose reductions. The authors believe that additional studies are warranted to characterize tumors that no longer respond to selumetinib. NCI is currently sponsoring an ongoing phase II trial of the drug for adults with NF1, in which serial tissue samples are being obtained. This study should provide information about possible mechanisms of resistance to selumetinib. In addition, a larger phase II pediatric trial is enrolling patients and should help establish the efficacy of selumetinib treatment in children. In this trial, in addition to tumor volume measurements, evaluations are being performed to assess the effect of selumetinib on plexiform neurofibroma related disfigurement, pain, quality of life, and function.