The overall objective is to demonstrate safety and efficacy of HIFU treatment of cutaneous neurofibromas located close to the surface of the skin in patients with the genetic disease Neurofibromatosis Type 1. The study will use a new investigational equipment that has been specially developed for dermatological therapy.

The study includes 20 patients in total distributed between the two centers, each having a minimum of 8 cutaneous neurofibromas eligible for treatment. All participants are adults (over 18 years) of both sexes.

The new treatment method is based on focusing intensive ultrasound just below the skin surface. This creates a very fast localized heating in small and very well-defined volumes containing neurofibroma tissue. This heating destroys or weakens the tissue, and the body's natural processes will subsequently transport affected cells away through the lymphatic and vascular systems. During the healing-process, the rejected tissue is replaced by new skin cells that are not expected to be fibrous.

The treatment is intended to be carried out without breaking the skin surface, and open wounds are therefore avoided. This is an essential advantage of the method compared to all existing therapies, which are based on physical removal of tumors through an open skin surface (e.g. surgery or laser therapy). Complications with risk of pain, infection and scarring will therefore be significantly reduced with the new proposed method.

The treatment is carried out by sending focused ultrasound from the handpiece of the equipment into the target area with neurofibromas. The equipment is set to send doses of approximately 150 milliseconds (0.15 seconds). The skin area and HIFU doses can be followed on the system computer screen and will be placed side-by-side with approximately 1-2 millimeter spacing. To achieve good energy transfer from handpiece to skin, ordinary ultrasound gel is used. There are no other special pre-treatments or preparations for the process. HIFU treatment is expected to be less painful than other treatments used. The treatment is quick, and typically takes less than 1 minute for a each area the size of a typical neurofibroma.

Inclusion Criteria:

• Males and females 18 years of age or older.
• Patients with a clinical diagnosis of NF1 based on germline genetic testing or by meeting the internationally recognized criteria given by the Clinical Care Advisory Board of the National Neurofibromatosis Foundation (now the Children's Tumor Foundation)
• Patients must be seeking active treatment for cNF.
• Patients must have ≥ 8 paired cNF that are visible and measure a minimum of 2 mm in size. These must be in areas amenable to treatment and surveillance.
• Patients with Fitzpatrick Type I to VI skin-type
• Able and willing to comply with all visits, treatments, evaluations, schedules, and requirements.
• Patients shall have received oral and written study information, accepted participation and signed the informed consent document.
• Patients who are willing and mentally and physically capable to understand and follow the treatment and follow-up schedule including post-treatment care instructions.
• Patients who are willing to have photographs and images taken of the treated lesions to be used anonymously or coded in evaluations and publications.

Exclusion Criteria:

• Patients who are undergoing other treatment modalities or investigational agents for their cNF lesions.
• Individuals who cannot give informed consent or adhere to study schedule.
• Patients who are actively tanning during the course of the study.
• Patients with adverse reactions to compounds of any external agent in use.
• Patients with known allergy to injectable anesthetics (relevant for biopsy only).
• Patients with any condition which, in the Investigator's opinion, would make it unsafe (for the participant or study personnel) to treat the participant as part of this research study.
• Patients, where target treatment may cause the acoustic beam to enter the eye.
• Pregnant females, due to possible discomfort with the procedure even though the procedure is localized and there is no new drug.
• Patients with tendency for keloid and hypertrophic scar formation .
• Patients with impaired wound healing.
• Patients with any other acute or chronic condition which, in the opinion of the investigator, could interfere with the conduct of the study.

Participants recieved a single treatment with the investigational device. Follow-up was conducted after 1 week, 3 months, 6 months, and 9 months.

The following criteria were used: U.S. Department of Health and Human Services. Common Terminology Criteria for Adverse Events (CTCAE). Version 5.0. Published online November 27, 2017. https://ctep.cancer.gov/protocoldevelopment/electronic\_applications/docs/CTCAE\_v5\_Quick\_Reference\_5x7.pdf