Introduction Tumor treating fields (TTFields) are low-intensity (1-3 v/m) intermediate
frequency (200 khz for GBM) alternating fields that disrupt cell division. The treatment
is increasingly used as a supplementary modality for patients with glioblastoma (GBM).
Recent randomized clinical studies have demonstrated tolerability of TTFields (Optune®,
Novocure®) for both newly diagnosed and recurrent GBM and a significant and sustained
survival benefit in the former population. Specifically, the addition of TTFields to
maintenance temozolomide (TMZ) therapy for newly diagnosed GBM patients, who had
completed initial concurrent radio-chemotherapy, resulted in significantly prolonged
median progression-free survival (PFS = 6.7 vs.#46; 4.0 months, p<0.001) and median overall
survival (OS = 20.9 vs.#46; 16.0 months, p<0.001) compared to maintenance TMZ therapy alone
(ef-14 trial) (4). Consequently, TTFields were recently approved by the US FDA and
included as a category 1 recommendation in the most recent guidelines from the National
Comprehensive Cancer Network (NCCN) for the treatment of newly diagnosed GBM. For
recurrent GBM, TTFields monotherapy has been shown to have equivalent efficacy and a
superior toxicity profile compared to best practice medical oncological therapy. This led
to US FDA approval for this indication in 2011. In addition, a post-hoc analysis of the
EF-14 dataset has indicated that the addition of TTFields to 2nd line medical oncological
treatment at first disease recurrence leads to an overall survival benefit. Finally, the
pride dataset showed that the addition of TTFields to current practice of medical
oncological treatment was beneficial.
Recently, the investigators proposed a novel approach to calculate the electrical field
distribution induced by TTFields therapy of GBM. The approach utilizes finite element
analysis and incorporates personalized MRI data to provide a realistic and individualized
estimate of the field intensity distribution, which is associated with the antimitotic
efficacy of the treatment. Using this approach, the investigators showed that targeted
skull-remodeling surgery, e.g. craniectomy or multiple burr-holes, can provide a
substantial and highly focused enhancement (~100%) of the median field intensity in
supratentorial tumors, while leaving the field distribution in healthy tissues
unaffected.
These results support the theoretical rationale that small and clinically feasible
craniectomies may improve the clinical efficacy of TTFields for cerebral hemispheric
tumors without compromising patient safety. Based on these findings, the investigators
recently concluded an open-label, single arm, prospective phase 1 trial (NCT02893137) to
investigate safety and feasibility of SR-surgery with TTFields and best practice
neuro-oncological therapy for recurrent GBM. The trial was active from December 2016 to
May 2019. The planned total number of patients was fifteen. Eligibility criteria included
age > 18 years, first recurrence focal supratentorial GBM (RANO), and KPS ≥ 70. Patients
were right-censored for OS and PFS at the time of analysis and excluded upon progression,
death, SUSARs, or unacceptable AEs. The primary endpoint was toxicity (CTCAEv4.0). The
secondary endpoints were OS, PFS, PFS rate at six months (PFS6), objective response rate
(ORR) based on the iRANO criteria (14), quality of life (QoL), Karnofsky performance
score (KPS), and steroid dose.20 patients were screened, 2 declined, and 3 had KPS < 70.
Of the 15 enrolled patients, 4 were excluded prior to TTFields due to
radionecrosis/non-recurrence, post-op infection, neurodeficit and withdrawal of consent,
respectively. All included patients (11 male and 2 female) had GBM IDH-wt tumors (4
MGMT-methylated). Median KPS was 90 (range 70-100) and median age 57 years (range 39 to
67). All patients received maximum safe resection at recurrence (4 had no residual tumor
(RANO), 5 non-measurable disease, and 2 measurable disease). 9 patients received adjuvant
bevacizumab monotherapy and 2 temozolomide rechallenge. The mean skull-defect area was
10.6 cm2 (range 7 to 37 cm2) and the median field enhancement 43 % (range 25 to 59%). The
median follow-up duration was 10 months and the median TTFields compliance 90% (range 48
to 98%). We observed no SUSARs, no grade 4/5 SAEs, 12 grade 3 SAEs (6 generalized
seizures in patients with known epilepsy, 1 post-op infection, 1 diarrhea, 1TIA, 1
fatigue, 1 headache and 1 DVT). The most common grade AE 1-2 was headache 60% CI95%= [32;
84], fatigue 53%, CI95%= [27; 79], skin rash 47%, CI95%= [21; 73], and nausea 40%, CI95%=
[16; 68].
Regarding survival results were PFS6 was 64%, CI95%= [35; 85], PFS= 8.8 months, CI95%=
[6.2; 13.2], OS= 15.0 months, CI95%= [9.6;16.2], and OS12= 64%, CI95%= [35;85]. One
patient had complete response during TTFields. Based on these results, the investigators
concluded that skull-remodelling surgery incl. craniectomy is not associated with
additional toxicity in combination with TTFields and best practice medical oncological
treatment and holds promising potential for improving TTFields outcome by focally
enhancing the field intensity in the tumor. The proposed phase 2 trial aims to validate
this hypothesis in a randomized comparative setting.
METHODS AND ANALYSIS Trial design The study is designed as an investigator-initiated,
prospective, multi-center, multi-national, randomized, minimax two-stage, comparative,
phase 2 trial, investigating superior efficacy of the intervention. Patients randomized
to the control arm will receive TTFields plus best physician's choice medical oncological
treatment (BPC treatment) and patients in the interventional arm will receive SR-surgery
in addition to TTFields and BPC treatment. The trial will enroll an expected sample size
of 70 patients from 4-6 scandinavian countries with Aarhus University Hospital, Denmark,
as the Sponsor and coordinating site. The primary outcome will be overall survival at 12
months (OS12) and the trial is designed to detect a 20% increase in OS12 in the
interventional arm compared to control (from 40% in the control arm to 60% in the
interventional arm). Secondary outcomes will include progression-free survival (PFS),
quality of life (QoL), clinical performance, and objective response rate (ORR). Interim
futility analysis will be conducted after 12 months follow-up of the first 52 patients.
The trial will be stopped at interim analysis if the OS12 months is lower in the control
arm compared to the interventional arm. The trial design and data reporting is in
accordance with the consort 2010 statement, the gnosis standards for neuro-oncology
trials, recent RANO recommendations for phase 2 trial design in neuro-oncology, and
general recommendations for phase 2/3 trial design (16-19). The study will be performed
in the period march 2020 to march 2023. The inclusion period is expected to be the first
24 months of the trial.
Participants Seventy (70) patients with progressive GBM according to RANO criteria will
be enrolled. Potential trial participants will be identified at an institutional
multidisciplinary neuro-oncological tumor boards and subsequently referred for
eligibility screening. All inclusion scans are assessed by a trained neuroradiologist.
Patients who are immediately ineligible, e.g. due to poor performance status, multifocal
disease, significant comorbidity, evidence of extracranial primary tumor, or other
excluding circumstances, will not be referred for screening.
Experimental intervention Patients will be randomised 1:1 to one of two study arms to
receive either, 1) SR-surgery, TTFields and best practice medical oncological therapy
(interventional arm), or 2) TTFields and best practice medical oncological therapy alone
(control arm). Best practice treatment will typically also include maximum safe
resection. Since the intervention (SR-surgery) is only effective during TTFields therapy,
TTFields will continue until 1) patient exclusion from the trial, 2) occurrence of a
suspected unexpected serious adverse reaction (SUSAR) related to the intervention, or 3)
ethical or medical safety contraindication for further TTFields therapy determined by the
investigators. This means that treatment may continue beyond progression, as long as
active treatment is indicated, and in some cases as compassionate use.
Sample size and statistical considerations The sample size calculations were based on a
randomized, comparative, minimax two-stage design and the binomial primary outcome of
OS12 for the patient population treated per protocol, i.e. for whom TTFields therapy was
initiated. This means that patients excluded prior to TTFields therapy initiation are not
included in the primary outcome analysis. Therefore, additional patients may be enrolled
to ensure that the planned sample receives active TTFields treatment. The aim of the
trial is to determine whether the intervention is superior to control and thus worthy of
further phase 3 investigation. The expected OS12 in the control arm is set to 40% based
on the EORTC 26101 trial, in which patients with first recurrence of GBM were treated
with lomustine monotherapy or lomustine/bevacizumab combination therapy. The trial showed
an OS12 of approximately 30% and we therefore set the expected level of OS12 to be
slightly above this threshold given the fact that TTFields is added to the treatment
which otherwise represents recommended practice. There are no current studies providing
accurate OS12 estimates for a population comparable to the study control arm and we
therefore based the estimate on an expected benefit of 10% from TTFields alone compared
to EORTC 26101. Setting the probabilities of false-positive and false-negative trial
results to α = 0.15 and 1-β = 0.80, respectively, and defining the expected target level
of OS12 to be OS12 = 0.6, i.e. a 20% absolute increase (and 50% relative increase)
compared to the control arm, we calculated a maximum sample size of n = 42 patients in
each arm (total n = 84) and an expected total sample size (en = 69.8). The expected
sample size en is calculated as en = n1 × pet0 + n × (1
- - pet0), where n1 = 52 is the
collective sample size of both groups at interim (stage 1) analysis, pet0 = 0.44 is the
probability of early futility termination.
The numbers are based on the given statistical
parameters and a two-stage minimax design as given in sh jung 2018. Interim futility
analysis will be conducted after endpoint assessment of 52 patients and the trial will be
terminated if the experimental arm performs worse than the control arm. In this case the
futility criterion will be defined as OS12experimental < OS12control and this conclusion
will determine futility at marginal power and significance levels of 1-β* = 0.80 and of
α* = 0.20, respectively. If the trial is not terminated at interim stage 1 analysis, the
trial will proceed to enroll a total of 84 patients and terminate when the final OS12
endpoint data have been obtained for all patients.
The secondary outcome measures of hazard rate ratios of PFS and OS will be tested using
the log-rank test at the 0.05 alpha level. Time-to-event endpoints will be estimated from
the time of randomization. Toxicity and adverse events will be reported using absolute
numbers and appropriate risk estimates. Final analysis will be conducted when all
patients have been excluded or censored, e.g. due to end-of-trial, or loss-to-follow-up.
Subgroup analysis based on prognostic factors will be performed, incl. analysis of
patient characteristics in each arm and identification of characteristics of potential
responders to the intervention. This will also include a correlation analysis between the
calculated field distribution and outcome estimates. Analyses will be based on both the
intent-to-treat population and the population proceeding to active therapy (per
protocol), i.e. At least four weeks of active TTFields therapy with ≥75% average
compliance.
Randomisation and blinding Patients will be randomised immediately upon enrollment in the
trial, i.e. prior to initial surgery. Randomisation will be performed using
randomization.com and patients will be randomised in a 1:1 ratio to receive TTFields and
best practice medical oncological treatment w/o skull remodeling surgery. The study
endpoint assessment committee will be blinded to the intervention. Local principal
investigators, co-investigators and sub-investigators will not be blinded, as optimal
array planning will require knowledge about skull-remodeling surgery. The operating
surgeon performing the skull-remodeling surgery will not be blinded. Patients will not be
blinded, as it will be possible for the patient to feel the skull configuration and
thereby determine whether SR-surgery was performed.
Risks and safety precautions General safety considerations concerning Optune® therapy are
outlined in the related technical and safety material provided by Novocure®. In general,
TTFields therapy is regarded a safe and recognized treatment for GBM. The most common
adverse effect is local skin rash in the area underlying the transducer arrays. The risk
of skin rash will be reduced by slightly moving the arrays during regular array changes.
Skin rash may be treated with topical corticosteroids, more frequent electrode
replacement and short pauses in TTFields therapy, if needed. The risk of brain injury due
to the skull remodeling aspect of surgery is minimal, as the entire operation is
performed extra-durally. Minor craniectomies do not pose a significant risk of mechanical
brain injury. For larger craniectomies, external protective headgear, such as a cap with
mechanical reinforcement over the unprotected brain area, may be used to reduce the risk
of traumatic brain injury after craniectomy. In the case of post-operative infection or
impaired wound healing, antibiotic therapy will be administered. If needed, surgical
revision/debridement of the wound and potentially removal of the bone flap may be
performed. In such cases, the patient may proceed to receive or continue TTFields therapy
at an appropriate time, if it is in the patient's best interest. TTFields therapy
following removal of the infected bone flap may be accepted even if the craniectomy size
exceeds 30 cm2. In all cases, the decision whether to continue with TTFields therapy
after surgery will be based on careful consideration of the expected safety and benefit
for the patient. All participants will be advised of situations and adverse events, in
which medical attention is required. Investigators or properly trained medical personnel
will be available for immediate attention or medical advice specific to the treatment or
protocol. Patients will receive contact information to the device support specialist,
whom they may contact in case of technical problems or considerations.
Monitoring and quality control The project will comply with international guidelines good
clinical practice (ICH-GCP and ds/en iso 14155:2012. Clinical investigation of medical
devices for human subjects
- - good clinical practice) and be monitored by the local
contract research organization (CRO).
Source data, verification of consent, and handling
of adverse events and near-miss incidents will be subject to 20% sampled monitoring. Full
access to all source data, incl. patient records, will be granted in relation to trial
inspection by the relevant national competent authorities. Experimental "waivers" from
the protocol will be registered in the project trial master file and reported to the
relevant authorities. Changes to the protocol will be submitted for approval by the
relevant authorities in accordance with GCP guidelines and regulations.
Dissemination All results will be published in peer-reviewed international scientific
journals and presented at international scientific conferences, regardless of academic
conclusions. Positive, negative, and inconclusive results will be publicly available.
