• Participant is capable of providing informed consent, which includes compliance with the requirements, prohibitions and restrictions listed in the informed consent form.

• Participant has been informed both verbally and in writing about the objectives of the clinical study, the methods, the anticipated benefits, the potential risks, and the discomfort to which they may be exposed and has given written consent to participation in the study prior to study start and any study-related procedure.

• Participant must be at least 18 years of age at the signing of the informed consent form (ICF).

• Participant must be able to swallow oral medication.

• Performance status: Participant must have a Karnofsky performance level of ≥70%. Note: Participants who are wheelchair bound because of paralysis secondary to a PN should be considered ambulatory when they are in the wheelchair. Similarly, participants with limited mobility secondary to the need for mechanical support (such as an airway PN requiring tracheostomy or CPAP) will also be considered ambulatory for the purposes of this study.

• Participant has been diagnosed with NF1 based upon the following diagnostic criteria:

• a. Clinical and imaging confirmation meeting at least two of the following NF1 diagnostic criteria in accordance with the clinical NIH consensus criteria: i. ≥ Six cafe-au-lait macules \> 1.5 cm in maximum diameter ii. Axillary and/or inguinal freckling iii. ≥ Two neurofibromas of any type, or ≥ 1 plexiform neurofibroma; iv. An optic pathway glioma (prior diagnosis without concurrent disease is acceptable) v. ≥ Five Lisch nodules (iris hamartomas). Note: must be confirmed on slit lamp exam by an ophthalmologist if this is one of only two criteria met for diagnosis vi. A distinctive bony lesion such as dysplasia of the sphenoid bone or dysplasia or thinning of long bone cortex vii. Biologic parent with confirmed diagnosis of NF1 viii. Genetic testing demonstrating a pathogenic NF1 germline mutation per CLIA-certified laboratory (or equivalent) testing.

⁃ 1\. Note: NF1 germline pathologic mutation positive must either be confirmed by the central laboratory or have documentation of NF1 mutation issued by a CLIA-certified laboratory (or equivalent). 2. No concern by the Investigator that an NF1 mimic, including but not limited to Noonan Syndrome, Legius Syndrome, or schwannomatosis could potentially serve as a more likely diagnosis

⁃ 7\. Participants satisfying the NF1 diagnostic criteria outlined in Inclusion Criterion #6 must also meet one of the following criteria:

⁃ a. Participant has at least one symptomatic PN (Target PN) measuring at least 3 cm on maximal cross-sectional (axial) diameter that is judged by the Investigator to be likely responsible for participant symptoms (such as pain, deformity, or neurologic disability), and unable to be completely resected without causing substantial damage/functional deficit, or unsuitable for surgery with high surgical risks.

⁃ b. Participant has an incompletely resected symptomatic PN with a postoperative residual of at least 15% of the primary lesion and measuring at least 3 cm on cross-sectional (axial) diameter.

⁃ c. Participant has a recurrent symptomatic PN measuring at least 3 cm in maximal cross-sectional (axial) dimension after prior resection.

⁃ 8\. Participants should have a minimum of seven measurable CN measuring 6-15 mm (if participants satisfy Inclusion Criterion #6 and have no CN or less than 7 CN they still might be considered for the study as judged by the Investigator and Sponsor).

• Measurable is defined as: 1. non-pedunculated (no stalk) 2. surrounded by visually uninvolved skin and not in physical contact with another CN, 3. measuring between 6 and 15 mm in the longest diameter and exophytic on visual exam (not macular).

• At least seven CN should be located on the trunk, neck, and/or limbs measuring between 6 and 15 mm in maximal diameter, and measurable as per the definition listed above.

• Participants with CN meeting the above criteria will undergo optional resections of at least two CN that meet eligibility criteria. If participant is willing to accept additional CN resections, this is permitted for up to four additional lesions after completion of six PAS-004 treatment cycles or after early withdrawal as long as there are sufficient lesions to allow efficacy assessment.

• 9\. Participant must be able and willing to undergo serial MRI scans as outlined in the study protocol.

• Note: Anxiolytic medication or pain medication as deemed clinically appropriate by the Investigator is permissible for the purposes of managing anxiety, claustrophobia, and pain during MRI.

• 10\. Participant must be able and willing to undergo serial 2-D and where available 3-D photography as well as caliper measurements as outlined in the study protocol.

• 11\. Participant must have an international normalized ratio (INR) and activated partial thromboplastin time (APTT) ≤ 1.5 x ULN.

• 12\. Participant must have adequate organ and bone marrow function at screening as indicated by the following laboratory value ranges:

⁃ a. Absolute neutrophil count (ANC) ≥ 1.5 × 109/L b. Hemoglobin ≥ 90 g/dL c. Platelets ≥ 100 × 109/L d. Serum total bilirubin ≤ 1.5 × ULN for age (≤ 3.0 × ULN in participants with Gilbert's syndrome) e. Serum total bilirubin ≤ 1.5 × ULN (Serum total bilirubin can be ≤ 3.0 × ULN if participants have hemolysis or congenital hemolytic diseases) f. Aspartate aminotransferase (AST) ≤ 2.0 × ULN g. Alanine aminotransferase (ALT) ≤ 2.0 × ULN h. Albumin ≥ 3 g/dL i. Creatinine clearance ≥ 60 mL/min

⁃ 13\. Participant must either agree to maintain abstinence (no heterosexual intercourse), or to use one highly effective form of contraception during study treatment and for at least 90 days after the last dose of investigational product (IP). Sperm-producing participants must agree not to donate sperm while receiving IP and for at least 90 days after the last dose of IP.