MEK Inhibitor Mirdametinib (PD-0325901) in Patients With Neurofibromatosis Type 1 Associated Plexiform Neurofibromas

Response will be determined by a blinded centralized review of volumetric MRI. The confirmed objective response rate (complete or partial response) by the end of Treatment Phase (i.e., Cycle 24) is defined as the proportion of participants who have a confirmed ≥ 20% reduction in target tumor volume as compared to baseline as assessed by a BICR, and the response needs to be confirmed by BICR in a consecutive tumor assessment within 2 - 6 months. Partial response is defined as a ≥ 20% reduction in target tumor volume from baseline. Complete response is defined as the complete resolution of the target tumor.

All adverse events were coded using MedDRA Version 24.0. Adverse events will be assessed according to toxicities graded by National Cancer Institute (NCI) Common Terminology Criteria for Adverse Events (CTCAE) Version 5.0.

Duration of response is defined as the time in months between the first instance of response that is subsequently confirmed, until the date of radiographic disease progression or death, whichever occurs first. For participants who enter the LTFU Phase, all MRI assessments in both the Treatment Phase and LTFU Phase will be used to determine duration of response. Participants without radiographic disease progression or death while on study will have their results censored to their most recent adequate (i.e. evaluable) tumor assessment date.

The PedsQL consists of a 23-item core measure of global QOL that can be completed in approximately 5 minutes. There is a total score and four subscales: physical functioning, emotional functioning, social functioning and school/work functioning. Participants ≥ 5 years of age complete an age-appropriate self-report; and parents/guardians of children ages 2-17 complete a parent proxy report of the age-specific QOL. The recall period is 7 days. PedsQL items are answered on a Likert scale with responses ranging from 0 to 4 (where 0 means it is never a problem and 4 means it is almost always a problem). These items are then reverse scored and linearly transformed to a 0-100 scale as follows: 0=100, 1=75, 2=50, 3=25, 4=0. On this scale, higher scores indicate better outcomes. Overall scale scores are calculated as the mean of the scores for the questions in said scale (or of all questions for the total score). The change from baseline is modelled using a mixed-model for repeated measures.

The NRS-11 is a self-reported 11-point numerical scale that assesses pain severity. Participants ≥ 8 years of age are asked to select a number from 0 (no pain) to 10 (worst pain you can imagine) that best describes their worst pain. The recall period is 24 hours. The change from baseline is modelled using a mixed-model for repeated measures.

The PII assesses relevant aspects of one's life, including pain interference with activities, spending time with family/friends, mood, sleep and attention. Participants ≥ 6 years of age complete a self-report, and parents/guardians of children aged 6-17 complete a parent proxy report. The recall period is 24 hours. The PII consists of 6 questions, each asking the responder to select one number from 0 to 6 that best describes how their/their proxy's pain has impacted various items over the past 24 hours with 0 representing "Not at all" and 6 representing "Completely". The mean of the completed items is taken as the PII score for a single assessment. The PII score presented each visit will be taken as the average of the PII scores over the 7 consecutive days up to and including visit day, with no transformation applied. The change from baseline is modelled using a mixed-model for repeated measures.

Assessment of strength will be conducted only in the area affected by the target tumor. Measurements will be obtained using Medical Research Council (MRC) grading followed by quantitative assessments using the sponsor provided MicroFET2 dynamometer. Dynamometer assessment (in lbs) must be conducted in accordance with the study reference manual. For each participant, the sum of the dynamometer scores for the muscle groups tested will be taken as an overall score for each visit with higher scores indicating better localized strength. To assess the change from baseline at a visit, a participant will need assessments in which all the following categories, as assessed at baseline, match at that visit: side affected, position during assessment (sitting/supine/lateral decubitus), muscle group assessed. The change from baseline in localized strength measured by the sum of the dynamometer scores for the muscle groups tested will be assessed at Cycle 13.

If motor dysfunction or weakness is evident, range of motion of the affected areas and/or joints will be measured by a goniometer.

If airway or lower extremity motor dysfunction is evident, endurance will be measured by completion of a 6-minute walking test.

Response will be determined by a blinded centralized review of volumetric MRI. Time to response is defined as the time in months from the start of treatment to the date of first response that was subsequently confirmed.

Evidence of progression or tumor growth will be determined by a blinded centralized review of volumetric MRI. Time to progression is defined as the time in months between the first treatment date until the date of radiographic disease progression. For participants who enter the LTFU Phase, all MRI assessments in both the Treatment Phase and LTFU Phase will be used to determine time to progression. Participants without radiographic disease progression will have their results censored to their most recent adequate (i.e. evaluable) tumor assessment date.

Evidence of progression or tumor growth will be determined by a blinded centralized review of volumetric MRI. Progression free survival is defined as the time in months between the first treatment date, until the date of radiographic disease progression or death, whichever occurs first. For participants who enter the LTFU Phase, all MRI assessments in both the Treatment Phase and LTFU Phase will be used to determine progression free survival. Participants without radiographic disease progression or death while on study will have their results censored to their most recent adequate (i.e. evaluable) tumor assessment date.

For participants with a PN that is visible and amenable to photography, changes in visible tumor aspects will be evaluated by a centralized reviewer.

Measured in tumor biopsies in participants ≥ 18 years of age.

The Pediatric Oral Medicine Acceptability Questionnaire (P-OMAQ) uses a 5-point numerical rate scale to measure acceptability of use of the tablet formulation with questions related to taste, smell and administration of study medication. Participants ≥ 8 years of age complete a 12-item self-report; adult parents/caregivers responsible for oversight of study drug administration for participants ages 6 months to 17 years complete a 19-item caregiver report. Each questionnaire is provided with a "past 7 days" recall with all items using a 5-point Numerical Rate Scale (1 to 5) with higher item-scores reflecting greater oral treatment acceptability. The overall P-OMAQ-P (pediatric self-report) and P-OMAQ-C (adult caregiver) scores for a participant in the study will be taken as the mean of all answered questions on the respective questionnaire.

If motor dysfunction or weakness is evident, strength of the affected muscle groups will be measured by dynamometer and assessed by a muscle grading scale. Medical Research Council (MRC) Scale grading (0-5) must be conducted in accordance with the study reference manual. MRC Grading is assessed on a scale of 0 to 5, with 0 representing no movement being observed, and 5 representing the muscle contracting normally against full resistance. To assess the change from baseline at a visit, a participant will need assessments in which all the following categories, as assessed at baseline, match at that visit: side affected, position during assessment (sitting/supine/lateral decubitus), muscle group assessed. The MRC Grade visit score is calculated for each participant separately, and these scores are then averaged.

PROMIS measures capability of physical functioning, with questions related to daily activities. Participants 8-17 years complete a self-report of physical function in the upper extremity or lower extremity (mobility), depending on the location of the PN. The recall period is 7 days. All PROMIS items are answered on a Likert scale with responses ranging from 1 to 5, with higher scores representing higher reported mobility. The total raw score will be calculated as the sum of the individual item responses at a given visit (total raw scale range 8-40). The total raw scores for the measure will be converted to T-scores using the applicable score conversion table in the user manual and scoring instructions (PROMIS, 2023) ranging from 14 to 59 for self-report, and 14 to 56 for parent proxy with higher scores representing higher reported mobility and better outcomes. A T-score of 50 indicates the population mean with a standard deviation of 10.

PROMIS measures capability of physical functioning, with questions related to daily activities. Participants 8-17 years complete a self-report of physical function in the upper extremity or lower extremity (mobility), depending on the location of the PN. The recall period is 7 days. All PROMIS items are answered on a Likert scale with responses ranging from 1 to 5, with higher scores representing higher physical functioning in the upper extremities. The total raw score will be calculated as the sum of the individual item responses at a given visit (total raw scale range 8-40). The total raw scores for the measure will be converted to T-scores using the applicable score conversion table in the user manual and scoring instructions (PROMIS, 2023) ranging from 10 to 57 for self-report, and 13 to 55 for parent proxy with higher scores representing higher reported physical functioning and better outcomes. A T-score of 50 indicates the population mean with a standard deviation of 10.

PROMIS measures capability of physical functioning, with questions related to daily activities. Participants ≥ 18 years with a target PN impacting physical functioning complete a self-report of physical function. The recall period is 7 days. All PROMIS items are answered on a Likert scale with responses ranging from 1 to 5, with higher scores representing higher reported physical capability. The total raw score will be calculated as the sum of the individual item responses at a given visit (total raw scale range 8-40). The total raw scores for the measure will be converted to T-scores using the applicable score conversion table in the user manual and scoring instructions (PROMIS, 2023) ranging from 20.3 to 60.1 with higher scores representing higher reported physical functioning and better outcomes. A T-score of 50 indicates the population mean with a standard deviation of 10.