A Phase I/II Study of the Cyclin-Dependent Kinase(CDK)4/6 Inhibitor Abemaciclib for Neurofibromatosis Type 1 (NF1) Related Atypical Neurofibromas

  • End date
    Dec 1, 2024
  • participants needed
  • sponsor
    National Cancer Institute (NCI)
Updated on 21 October 2022
renal function
absolute neutrophil count
ejection fraction
serum pregnancy test
measurable disease
gilbert disease
plexiform neurofibroma
nf1 mutation



NF1 is a genetic disease that causes tumors called atypical neurofibromas. These tumors, which arise from nerves, can cause serious medical problems. The only treatment is surgery. Researchers want to see if a drug called abemaciclib can help.


To find a safe, tolerable dose of abemaciclib for treating atypical neurofibromas.


People ages 12 and older who have NF1 and have one or more atypical neurofibromas that cannot or will not be removed with surgery


Participants will be screened with:

Medical history and physical exam

Blood, urine, and heart tests

MRI: Participants will lie in a machine that takes pictures of the body. A padding or coil will be placed around their head. They may have a contrast agent injected into a vein.

Biopsy sample: A small piece of tumor will be removed using a large needle.

Participants will have frequent visits during the study. These will include repeats of the screening tests as well as the following:

PET scan: Participants will lie in a machine that takes pictures of the body. They will have a contrast agent injected into their arm.

Questionnaires about the effects of abemaciclib on pain and quality of life

Possible photographs of tumors

Participants will take abemaciclib capsules orally twice daily in 28-day cycles. They will take the drug for up to 2 years. Some may be able to take it for longer.

Participants will have a follow-up visit about 30 days after their last dose of the study drug. Then they will have visits every 3 months for 1 year.



Neurofibromatosis type 1 (NF1) is a genetic tumor predisposition syndrome (incidence of 1:3000), which results in the development of progressive tumor and non-tumor manifestations, the majority of which have no effective medical therapies. 25-50% of individuals with neurofibromatosis type 1 (NF1) develop histologically benign plexiform neurofibromas (PN), which can cause substantial morbidity. Recently, the POB identified that MEK inhibitors cause shrinkage of the majority of PN and that PN shrinkage is associated with clinical benefit.

A natural history study of NF1 at the NCI has gathered comprehensive imaging information using longitudinal whole-body MRI with volumetric measurements. By this approach, distinct nodular lesions (DNL) were identified, many of which are atypical neurofibromas (ANF) based on pathology review.

The NCI POB and others have described ANF as precursor lesions for aggressive soft tissue sarcomas called malignant peripheral nerve sheath tumors (MPNST), which show poor response to chemotherapy and have poor survival. Of note, ANF appear to be less responsive to treatment with MEK inhibitors indicating a different biology.

Exome sequencing of 16 ANF resected at the National Cancer Institute, Pediatric Oncology Branch (NCI POB) and Belgium revealed that 90% of the cases had heterozygous loss of CDKN2A/B as the only new somatic change in addition to biallelic NF1 deletion, consistent with prior reports. These results demonstrate that transformation of NF1 nerve tumors may genetically proceed through the premalignant ANF by a common mechanism that might be a point of intervention.

CDKN2A is the primary inhibitory brake on CDK4/6 driven signaling and is commonly deleted in glioblastoma, pancreas, bladder, breast and prostate cancer. The specific CDK4/6 inhibitor, abemaciclib, has FDA approval for the treatment of metastatic breast cancer.

ANF is a prototypic premalignant lesion for testing experimental intervention, as these lesions are at risk for transformation, and share a common potentially druggable genomic alteration (CDKN2A/B deletion). We propose a clinical trial of abemaciclib in children and adults with NF1 and unresectable ANF.


Phase I: To determine the recommended Phase II dose (RP2D) of abemaciclib in patients with NF1 and a measurable ANF.

Phase II: To determine the objective response rate (ORR) in the target ANF; complete and partial response (CR + PR), response determined by volumetric MRI analysis (^3 20% volume reduction) compared to baseline.


Patients must be at least 12 years of age with a diagnosis of NF1 with associated age-related requirements as follows:

Willingness of patients >= 12 years old and <18 years old to undergo pre-treatment percutaneous biopsy of ANF if deemed feasible with minimal morbidity

Willingness of patients >=18 years old to undergo pre-treatment and on-treatment percutaneous biopsy of ANF if deemed feasible with minimal morbidity

Presence of >= 1 measurable ANF (biopsy confirmed) for which surgical removal could cause significant morbidity OR for which patient is unwilling to undergo surgical resection OR the presence of more than one distinct nodular lesion (DNL) including at least 1 biopsy proven ANF

For patients of all ages with ANF who cannot be safely biopsied with minimal morbidity, biopsy requirement to be performed at NIH Clinical Center will be waived from eligibility criteria. In this case, review of available archival tissue by NIH Pathology will be necessary to confirm diagnosis of ANF, which is mandatory for eligibility.


This is a Phase I/II non-randomized, open label, single institution study of the CDK4/6 inhibitor, abemaciclib, in children and adults with NF1 and a measurable ANF or with multiple ANF/DNL.

Primarily because the tolerability of investigational agents may differ between the NF1 population and non-NF1 population and secondarily because abemaciclib has not been evaluated in children to date, there will be a limited dose finding phase.

During the Phase 1 portion of the trial, the first 6 subjects enrolled will be treated at 75% of the adult recommended Phase II dose (ARP2D; 150mg PO BID) of abemaciclib used in patients with malignancies, in a 28-day cycle. For patients < 18 years of age, dosing will be based on body surface area (BSA).

Cohorts of up to 6 subjects will be enrolled, with dose adjustment depending on dose-limiting toxicities (DLT) until the maximum tolerated dose (MTD)/ recommended Phase II dose (RP2D) is established.

The Phase II trial is a Simon minimax two-stage trial design. An observed response rate of approximately 30% or greater would be considered desirable. The first stage of the Phase II portion of the trial will enroll 15 evaluable subjects; if 0 to 2 of the 15 have a PR or CR, then no further subjects will be accrued. If 3 or more of the 15 subjects have a PR or CR, then accrual would continue until a total of 21 evaluable subjects have been enrolled in phase II.

The accrual ceiling will be set at 50 eligible subjects (to include patients who are screened but found to not be eligible to undergo treatment).

All patients will undergo careful toxicity monitoring. Restaging MRI for response will be performed pre-cycles 3 and 5, and then every 4 cycles for remainder of the first year.

Condition Neurofibromatosis 1
Treatment Abemaciclib
Clinical Study IdentifierNCT04750928
SponsorNational Cancer Institute (NCI)
Last Modified on21 October 2022


Yes No Not Sure

Inclusion Criteria

Patients must have a clinical diagnosis of NF1, i.e., patients must have at least two of the diagnostic criteria for NF1 listed below (NIH Consensus conference) or a confirmed
NF1 mutation from a CLIA-certified laboratory
\-- Six or more cafe-au-lait macules (>= 0.5cm in prepubertal subjects or >=
5 cm
in post pubertal subjects)
Freckling in axilla or groin
A neurofibroma or plexiform neurofibroma
Optic glioma
Two or more Lisch nodules
A distinctive bony lesion (dysplasia of the sphenoid bone or dysplasia or thinning of long bone cortex)
A first-degree relative with NF1
Presence of >= 1 ANF (biopsy confirmed) for whom surgical removal could cause significant clinical morbidity OR for which patient is unwilling to undergo surgical resection OR the presence of more than one distinct nodular lesion (DNL) including at least 1 biopsy proven ANF
NOTES: Definition of DNL. In addition, there will not be a requirement for confirmed
CDKN2A/B deletion for study eligibility due to known biopsy sampling error and tumor
Age >= 12 years old (no maximum age) with associated age-related requirements as
Age >= 12 years old with BSA >= 0.71 M^2 and able to swallow whole tablets
Willingness of patients >= 12 years old and <18 years old to undergo pre-treatment
percutaneous biopsy of ANF if deemed feasible with minimal morbidity
Willingness of patients >=18 years old to undergo pre-treatment and on-treatment
percutaneous biopsy of ANF if deemed feasible with minimal morbidity
NOTE: For patients of all ages with ANF that cannot be safely biopsied with minimal
morbidity, biopsy requirement to be performed at NIH Clinical Center will be waived from
eligibility criteria. In this case, review of available archival tissue by NIH Pathology
will be necessary to confirm diagnosis of ANF, which is mandatory for eligibility
Prior Therapies
Measurable disease: Patients must have at least one measurable ANF defined as a lesion
of at least 3 centimeters (cm) measured in one dimension. Measurability and
suitability for volumetric MRI analysis of the target ANF must be confirmed with the
peripheral neuropathy prior to enrollment before entering this study
NCI POB prior to enrolling a patient. The target ANF will be defined as the clinically
most relevant ANF, which has to be amenable to volumetric MRI analysis
Since there is no standard effective chemotherapy for patients with NF1 and ANF
patients may be treated on this trial without having received prior medical therapy
Adequate performance scale (Lansky/Karnofsky >=70%)
directed at their ANF
Adequate organ function as defined below
Investigational agents/biologic therapies (not chemotherapy): Patients who have
received previous investigational agents or biologic therapies are eligible for
enrollment. At least 30 days or 5 half-lives must have elapsed since receiving medical
therapy directed at any NF1 related tumor. Patients who received prior medical therapy
Age (years) is >12 and <=15 then Maximum Serum Creatinine (mg/dL) = 1.2
for a NF1 related tumor manifestation must have recovered from the acute toxic effects
Age (years) is >15 then Maximum Serum Creatinine (mg/dL) = 1.5
of all prior therapy to grade 1 CTCAEv5 except for residual alopecia or Grade 2
Chemotherapy agents: Patients who received chemotherapy must have recovered (CTCAE
Grade <=1) from the acute effects of chemotherapy except for residual alopecia or
Grade 2 peripheral neuropathy prior to enrollment. A washout period of at least 28
days is required between last chemotherapy dose and enrollment (provided the patient
did not receive radiotherapy)
Patients who received adjuvant radiotherapy must have completed and fully recovered
from the acute effects of radiotherapy. Patients who have received previous radiation
therapy are eligible for enrollment. At least 6 weeks must have elapsed since the last
radiation therapy and start of treatment. The only target ANF cannot have received
radiation previously
At least 28 days must have elapsed since any major surgeries, with evidence of good
wound healing. Minimally invasive biopsies and central line placements are not
considered major surgeries
Patients who have received prior treatment with abemaciclib or another specific CDK4/6
inhibitor are not eligible for enrollment
Hematologic Function: Patients must have an absolute neutrophil count >=
mililiters, hemoglobin >= 9 g/dL (transfusion independent, defined as not
receiving blood transfusion unless related to trauma or surgeries), and platelets less
than or equal to 100,000/mililiters (transfusion independent, defined as not receiving
platelet transfusions unless related to trauma or surgeries)
Hepatic Function: Patients must have bilirubin within 1.5 x the upper limit of normal
for age, with the exception of those with Gilbert syndrome, and AST/ALT within <= 3 x
upper limit of normal
Renal Function: Patients must have a creatinine clearance or radioisotope GFR
>=60ml/min/1.73 m^2 or a normal serum creatinine based on age, described below
Cardiac Function: Normal ejection fraction (ECHO or cardiac MRI) >= 53% (or the
institutional normal; if a range is given then the upper value of the range will be
used); QTC or QTcF <=450 msec
Willingness to avoid grapefruit or grapefruit juice during abemaciclib
Informed Consent: Ability of subject or Legally Authorized Representative (LAR)
to understand and the willingness to sign a written informed consent document
All patients or their legal guardians (if the patient is < 18 years old) must
sign an IRB-approved document of informed consent to demonstrate their
understanding of the investigational nature and the risks of this study before
any protocol-related studies are performed. When appropriate, pediatric subjects
will be included in all discussions
Based on animal studies, the effects of abemaciclib can cause fetal harm. For
these reasons, women of child-bearing potential and men must agree to use a
highly effective contraceptive method during treatment and for at least 3 months
after the last dose of abemaciclib. Should a woman become pregnant or suspect she
is pregnant while she or her partner is participating in this study, she should
inform her treating physician immediately. Men treated or enrolled on this
protocol must also agree to use adequate contraception prior to the study, for
the duration of study participation, and 4 months after completion of abemaciclib
Woman subjects of childbearing potential (WOCBP) must have a negative serum pregnancy
test within 7 days of the first dose of abemaciclib
A woman is considered to be of childbearing potential if she is postmenarcheal, has
not reached a postmenopausal state (>= 12 continuous months of amenorrhea with no
identified cause other than menopause), and has not undergone surgical sterilization
(removal of ovaries and/or uterus)
Contraceptive methods may include intrauterine devices (IUD), or barrier method, a
spermicidal agent should be added as a double barrier protection; abstinence is also
Cases of pregnancy that occur during maternal exposures to abemaciclib should be
reported. If a patient or spouse/partner is determined to be pregnant following
abemaciclib initiation she must discontinue treatment immediately. Data on fetal
outcomes and breastfeeding are to be collected for regulatory reporting and drug
safety evaluation

Exclusion Criteria

Patients with interstitial lung disease
Requires treatment with strong CYP3A inhibitors or inducers
Inability to swallow tablets, since tablets cannot be crushed or broken
Pregnant women, or women who intend to become pregnant during the study, are excluded
from this study because of the teratogenic effects of abemaciclib. Because there is an
unknown but potential risk for adverse events in nursing infants secondary to
treatment of the mother with these agents, breastfeeding should be discontinued if the
mother is treated on study
May not have a NF1-related tumor such as optic pathway glioma or malignant peripheral
nerve sheath tumor, which requires treatment with chemotherapy or surgery
Serious preexisting medical condition(s) that would preclude participation in this
study (for example, interstitial lung disease, severe dyspnea at rest requiring oxygen
therapy, history of major surgical resection involving the stomach or small bowel that
would preclude adequate absorption, or preexisting Crohn s disease or ulcerative
colitis or a preexisting chronic condition resulting in baseline Grade 2 or higher
Uncontrolled intercurrent illness including, but not limited to, symptomatic
congestive heart failure, unstable angina pectoris, cardiac arrhythmia, active
bleeding diatheses or renal transplant, or psychiatric illness/social situations that
would limit compliance with study requirements
Personal history of any of the following conditions: syncope of cardiovascular
etiology, ventricular arrhythmia of pathological origin (including, but not limited
to, ventricular tachycardia and ventricular fibrillation), or sudden cardiac arrest
Active bacterial infection (requiring intravenous [IV] antibiotics at time of
initiating study treatment), fungal infection, or detectable viral infection (such as
known human immunodeficiency virus positivity or with known active hepatitis B or C
[for example, hepatitis B surface antigen positive]. Patients with HIV who have
adequate CD4 counts and who have no requirement for antiviral therapy will be
eligible. NOTE: Screening is not required for enrollment
Inability to undergo MRI and/or contraindication for MRI examinations following the
MRI protocol (see Study Procedure Manual). Prosthesis or orthopedic or dental braces
that would interfere with volumetric analysis of target ANF on MRI
Refractory nausea and vomiting that would limit drug administration in the opinion of
the Principal Investigator
Known severe hypersensitivity to abemaciclib or any excipient of abemaciclib or
history of allergic reactions attributed to compounds of similar chemical or biologic
composition to abemaciclib
Clinical judgment by the investigator that the patient should not participate in the
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