Introduction
Colorectal cancer is one of the most commonly diagnosed cancers, and metastatic disease
continues to be frequent. In a number of patients, symptoms arise from the tumor in
the colon or rectum, leading to a complicated clinical course with obstructive symptoms,
pain, or bleeding and resulting in reduced quality of life.
Electroporation utilizes brief electric pulses to permeabilize the cell membrane,
which facilitates transport of molecules [1 ] such as calcium (calcium electroporation) [2 ]. Calcium electroporation is a promising anticancer treatment and has been tested
in preclinical [3 ]
[4 ]
[5 ]
[6 ]
[7 ]
[8 ]
[9 ]
[10 ] and clinical studies [11 ]
[12 ]
[13 ]
[14 ]. Studies investigating calcium electroporation for cutaneous metastases have shown
that the treatment is safe and feasible with promising results [11 ]
[13 ]. A recent study in recurrent head and neck cancer showed a clinical response in
three of six patients [14 ]. Interestingly, studies have found an indication that calcium electroporation initiates
a favorable immunologic response, which potentially may be used in a multimodal treatment
strategy in the future.
However, calcium electroporation for colorectal cancer has not yet been tested in
a clinical setting. We here report the first clinical study of calcium electroporation
for colorectal cancer. The aim of the trial was to evaluate the safety of the procedure.
Patients and methods
Setting
This was an exploratory phase I study investigating the safety of endoscopic calcium
electroporation for colorectal cancer. The study was planned to include six patients
with inoperable colorectal cancer. Patients were recruited at Zealand University Hospital,
Denmark. The protocol was approved by the Danish Medicines Agency, the Regional Ethics
Committee (H-16036390) and the Danish Data Protection Agency (REG-189–2017). Clinicaltrials.gov
identifier: NCT03542214.
Patients
Eligible patients had histologically verified inoperable colorectal. Patients were
reviewed by a multidisciplinary team before inclusion. Inclusion criteria were: age > 18
years, treatment-free interval of a minimum of 2 weeks, World Health Organization
Performance Status ≤ 2, patients deemed capable of understanding the given information
and written informed consent, thrombocytes ≥ 50 billion/L, and estimated glomerular
filtration rate (eGFR) > 40 mL/min. Ineligibility criteria were pregnancy, implanted
colon stent, implantable cardioverter-defibrillator or pacemaker, non-correctable
coagulative disorder, highly inflamed colon tissue with ulceration and bleeding, or
any other clinical condition or previous treatment that, in the investigators’ opinion,
made the patient ineligible.
Screening
After informed consent was signed, patients were examined with an electrocardiogram
(EKG) and blood biochemistry. In addition, a nurse who specialized in nurse-administered
propofol sedation (NAPS) assessed whether the patients were eligible for NAPS. Exclusion
criteria were ASA > II, body mass index > 35, sleep apnea, high risk of respiratory
complications, and previous complications associated with anesthesia.
Bowel preparation
Individual recommendations for bowel preparation were given. For patients with a rectal
tumor, enema was found to be sufficient as preparation before the procedure.
Anesthesia
The procedure was performed on an outpatient basis under NAPS. The initial bolus of
propofol was 100 mg minus patient age (maximum of 60 mg), followed by a bolus (50 %
of initial dose) after 45 to 60 seconds. A repeated bolus (5 mg) was provided with
a 30– to 40-second interval during the procedure according to institutional guidelines.
Injection of calcium chloride
The dosage of calcium chloride was estimated from preclinical studies [3 ]
[4 ]
[9 ]
[15 ]. Calcium chloride was administered intratumorally with a 4-mm endoscopic injection
needle. The investigator prepared calcium chloride in the Operating Room and the preparation
was countersigned by an observer, as previously described [14 ]. Calcium chloride with a concentration of 0.5mM (SAD, Denmark) was dispensed in
a solution with isotonic NaCl: (6.75 mL calcium chloride + 8.25 mL NaCl = 15 mL solution
with 9 mg/mL or 0.225 mmol/mL calcium chloride).
The injected dose of calcium chloride was defined by the surgeon based on assessment
of tumor volume through visualization with an endoscope. As a safety measure, the
maximum dosage was set at 13 mL of calcium chloride. This was calculated from a desired
maximum rise in Ca2 + of 0.2 mmol/L extracellular volume (approximately 15 L of extracellular volume ×
0.2mmol/L = 3 mmol calcium chloride: 3 mmol/0.225 mmol/mL ≈ 13 mL calcium chloride).
It was expected that a significant amount of calcium chloride would leak out due to
the stiffness of tumor tissue.
Endoscopic electroporation
The EndoVE device (Mirai Medical, Cork, Ireland) was used. EndoVE is a single-use
device that can be attached to a standard endoscope. The device was connected to a
vacuum system to draw tumor tissue into contact with the chamber. The device was connected
to a square wave pulse generator (Cliniporator EPS01, Italy). The pulse generator
delivered a series of eight pulses of 0.1 ms duration with a frequency of 1 kHz and
an amplitude of 1 kV/cm.
Endoscopic procedure
Before injection of calcium chloride, the tumor was inspected and photographed, and
biopsies were collected. After biopsies were collected, calcium chloride was injected
intratumorally. After injection, the EndoVe device was attached. The device was placed
on the tumor, and vacuum suction secured the position. Repositioning of the electrode
was performed after each series of electrical pulses until the entire tumor area was
covered or to the extent possible. The treatment was performed by two experienced
endoscopic surgeons.
After treatment, patients were observed for at least 20 minutes.
Follow-up
A follow-up visit after 1 week was planned, with clinical examination and blood samples.
Furthermore, patients had a follow-up visit with blood samples and endoscopy with
biopsies approximately 4, 8, and 12 weeks and 6 months after initial study treatment,
if possible. Additional treatment with calcium electroporation could be offered in
case of remaining tumor tissue, and if the repeated procedure was deemed suitable.
A maximum of three treatments were offered with a minimum interval of 4 weeks.
Primary endpoint
The primary endpoint was safety of the procedure. Safety evaluation was performed
using reported adverse events (AEs) according to Common Terminology Criteria for Adverse
Events (CTCAE) version 4.0.
Secondary endpoints
Pain
Pain in relation to the procedure and pain from the primary tumor at follow-up were
evaluated through the numeric rating scale (NRS) pain score. In NRS, patients are
asked to indicate a number between 0 and 10. Zero represents no pain at all whereas
the upper limit represents the worst pain ever possible. NRS was recorded at baseline,
Day 1, and at each follow-up visit.
Patient-reported symptoms
Patient-reported symptoms, including pain, bleeding, stenosis, and diarrhea were registered
at inclusion and at each follow-up.
Manual assessment of major histopathological differences
Unblinded matched biopsies were compared for obvious differences that would not be
identified by the quantitative analysis as i. e. ischemic changes or hyperplasia.
Immunohistochemical staining and histopathological analysis
Potential local immunologic response after treatment was evaluated. Analysis of PD-L1
expression was performed to identify potential targets for anticancer treatment. Serial
sections of FFPE blocks of 4 µm were cut. The first slide was stained with hematoxylin
and eosin (HE). Immunohistochemical staining was performed using anti-PD-L1 clone
22C3 (Agilent/Dako, Glostrup, Denmark, cat# M3653), anti-CD3 clone LN10 (Leica/Triolab
AS, Broendby, Denmark, cat# NCL-L-CD3–565) and anti- CD8 clone C8 /144B (Agilent/Dako,
cat# GA623). All staining was performed as double-labelling with anti-Cytokeratin
clone BS5 (Nordic Biosite Aps, Copenhagen K, Demmark, cat# BSH-7124–1) on the automated
instrument Omnis (Agilent/Dako), and details of protocols are outlined in Supplementary 1 . For PD-L1, a previously published detailed protocol was followed [16 ].
Quantitative digital image analysis of CD3- and CD8-positive lymphocytes
Identification of a potential tumor-specific immune response was performed through
analysis of CD3- and CD8-positive lymphocytes. All slides were scanned using a Leica
SCN400 slide scanner and subsequently the digital images were uploaded to Visiopharm
Quantitative Digital Pathology software, version 2020.09 (Hoersholm, Denmark). For
the CD3/cytokeratin- and CD8/cytokeratin-stained slides, an Application Protocol Package
(APP) was developed for the quantitative analysis. The APP was built around a process
consisting of several sequential steps. At first four separate regions of interest
(ROI) was outlined on a HE-stained slide from each tissue block. The tissue was divided
into compartments consisting of ulceration; granulation tissue; invasive cancer or
areas suspicious of invasive cancer; and non-malignant colon mucosa. Next, the tissue
align module was applied on serial sections stained with HE, CD3/cytokeratin and CD8/cytokeratin
to ensure analyzing identical ROI. The quantitative analysis was conducted at 20-×
magnification. The defined output variables were area in mm2 of each ROI, number of CD3- and CD8-positive cells and density of positive cells
per mm2 within the ROI, respectively. [Fig. 1 ] illustrates the process of the digital analysis.
Fig. 1 Illustrating the process of the digital analysis of CD3 and CD8. In this example CD3
is visualized. a Visualizing the process of marking different compartments off the tissue. Green marks
normal tissue, red marks cancer, blue marks ulcerous tissue. b CD3. c CD3 labelled.
Manual assessment of PD-L1 expression
Assessment was performed by a senior pathologist specialized in colorectal cancer.
First, the PD-L1 expression was assessed manually on the blinded biopsies. Primary
evaluation was performed at ×4/×10 magnification to establish an overview, followed
by ×20 magnification for evaluation of tumor and immune cells. Convincing partial
or complete linear membranous staining was required for classifying a tumor cell as
positive. Convincing membranous and/or cytoplasmic staining were required for classifying
an immune cell (lymphocytes and macrophages) as positive. Any degree of staining intensity
counted as positive. The cellular localization (tumor cells; predominantly tumor cells;
immune cells; predominantly immune cells; or an evenly distributed positive reaction
between tumor cells and immune cells) and number of positive cells (none, few, moderate
or high number of positive cells) was registered. Few positive cells were defined
as “scattered positive,” whereas a high number was defined as clustered or bandlike
arranged cells. Next, on the matched unblinded material, it was estimated if the number
of PD-L1 positive cells had increased, decreased or was identical, before and after
treatment.
Quantification of circulating cell-free DNA
Prior to cell-free DNA (cfDNA) purification, a 191-bp DNA spike-in fragment was added
to the plasma [17 ]. Extraction of plasma cfDNA was performed using a Perkin Elmer Chemagic 360 Robot
(Waltham, Massachusetts, United States), with a CMG-1304 kit according to the manufacturer’s
recommendations. All samples were analyzed using digital droplet PCR (ddPCR) on a
QX-200 system from Bio-Rad (Hercules, California, United States). Levels of spike-in
control were measured together with levels of immunoglobulin gene rearrangement that
was used as a control for potential contaminating lymphocyte DNA [17 ]. Further, a fragmentation ratio analysis was performed by measuring levels of 65
base pairs (bp) and 250 bp fragments of the EMC7 housekeeping gene [18 ]. The EMC7 65 bp assay was also used to quantify the total levels of cfDNA.
Radiological assessment
Evaluation of treatment response also included imaging of primary tumor and distant
metastasis. For patients with a rectal tumor, thoraco-abdomino-pelvic computed tomography
(CT) scans and rectal magnetic resonance imaging (MRI) were performed at baseline
< 1 month after initial treatment with calcium electroporation. Follow-up scans were
performed at 4, 8, and 12 weeks and after 6 months to the extent possible. For patients
with a colonic tumor, only CT scans were performed.
CT scans were performed with 80– to 100-mL IV contrast Iomeron 350 mg Iodine/mL.
The thoraco-abdomino-pelvic CT scans were performed using different CT scan systems;
PHILIPS 64-slice Brilliance, PHILIPS iCT 256 slice, SIEMENS Force, SIEMENS Drive,
SIEMENS Edge. Images were recorded 70 seconds after intravenous injection of 80 to
100 mL Iomeron 350 mg/mL (Bracco) given at an injection rate of 3 mL/second. No bowel
preparation was used. However, oral administration of 1 L of water 15 minutes prior
to the scan was used to delineate the small and large bowel. Images were analyzed
in the Centricity Radiology Information System and Centricity Picture Archiving and
Communications System (PACS–GE Healthcare) and interpreted on an Impax PACS workstation
(GE Healthcare).
Scans were evaluated through standard evaluation and tumor T-stage was assessed by
radiologists using the 8th version of the TNM classification system. Metastasis were evaluated according to
RECIST 1.1 criteria [19 ]. Response criteria are defined as follows: complete response (CR) with disappearance
of all lesions, partial response (PR) ≥ 30 % decrease in the sum of diameters of target
lesions from baseline, stable disease (SD) neither CR, PR or progressive disease (PD) ≥ 20 %
increase in the sum of diameters of target lesions from baseline.
MRI scans were primarily performed on a 3 T Siemens MAGNETOM Vida (70 cm). Two other
MRI scans were used: 1.5 T Siemens MAGNETOM AvantoFit (60 cm) and 1.5 T Siemens MAGNETOM
Aera (70 cm). MRI scans were performed using T2 sequences axial, coronal and sagittal
to the tumor, and diffusion axial to the patient. Like CT, the MRI scans were evaluated
through standard evaluation and tumor T-stage was assessed by radiologists using the
8th version of the TNM classification system.
Statistical analysis
Due to the small sample size of the study and the variability of time between available
blood sample and tissue, no formal statistical tests were performed. The concentration
of cfDNA at the various time points was plotted for each study participant. The density
of CD3- and CD8-positive cells were calculated for each individual tissue compartment
present in the biopsies and plotted at the various time points for each study participant.
Results
The study included six patients, five with rectal cancer and one patient with sigmoid
colon cancer, from Zealand University Hospital, Denmark, from April 2018 to January
2020. Five male and one female patient aged 42 to 83 with WHO performance 0 to 2 were
included in the study. Of the included patients, three had been undergoing systemic
chemotherapy before entering the protocol. Patient characteristics are shown in [Table 1 ].
Table 1
Patient characteristics.
Patient
Gender
Age
ASA
Performance (WHO)
Tumor stage
Tumor length
Circumferential extent
Metastasis
Local symptoms
Previous treatment
1
M
82
2
1
T2N2M1
5 cm
Not passable with endoscope
Liver
Pain, bleeding, stenosis
None
2
M
80
2
1
T3N2M1
6 cm
Not passable with endoscope
Lymph node
Stenosis
Capecitabine + bevacizumab 14 cycles
3
M
83
2
2
T3N1M1
5 cm
> 75 %
Liver
Pain, bleeding, stenosis
None
4
M
49
1
0
T4N2M1
7 cm
100 %
Liver
Bleeding, stenosis
FOLFIRI + panituzumab 14 cycles and FOLFOX + bevacizumab 7 cycles
5
F
42
2
0
T3N0M1
6 cm
> 60 %
Liver and lung
Diarrhea
FOLFIRI 11 cycles
6
M
69
2
0
T3N1M1
6 cm
> 75 %
Liver and lung
Stenosis, diarrhea
None
ASA, American Society of Anesthesiologists; WHO, World Health Organization; FOLFIRI,
folinic acid, fluorouracil, irinotecan; FOLFOX, folinic acid, fluorouracil, oxaliplatin.
A total of 10 procedures with calcium electroporation were performed. Of the six patients,
three patients had a second treatment with calcium electroporation and one patient
had three treatments. Patients no. 3 and 5 were offered additional treatments with
a time interval of 4 weeks and patient no. 6 with a time interval of 3 weeks as requested
by the patient. In two patients, we were unable to deliver a second treatment due
to insufficient bowel preparation.
Patients no. 2 and 5 were offered calcium electroporation as an additive treatment
and continued systemic chemotherapy after the procedures. Patient no. 6 was followed
with an interval of approximately 3 months from the initial treatment to first follow-up.
Systemic chemotherapy was initiated 3 weeks after calcium electroporation and the
patient requested a delay of an additional treatment.
Treatment procedure
The procedures were initiated with inspection and biopsies from the tumor area. In
two cases (patients no. 1 and 2) the tumor was not passable with the endoscope; however,
it was possible to treat the anal part of the tumor. In one case (patient no. 4) the
tumor was passable with the endoscope; however, the area was narrow due to a circumferential
extent of almost 100% and only approximately 50 % of the tumor was accessible to the
EndoVe device. In the final three cases, inspection found circumferential extent of
> 60 % in one patient (no. 5) and > 75% in two patients (no. 3 and 6). In the initial
procedure, 75 % of the tumor surface area was treated and at the additional treatment
it was possible to cover 100 % of the tumor surface area.
After inspection and evaluation of the tumor, calcium chloride was injected intratumorally.
A median dose of 11 mL (range 3–13 mL) was administered. After injection of calcium
chloride, the EndoVe device was attached to the endoscope and a median of eight series
of pulses (range 3–13) were applied to the tumor area, with a median current (A) of
12 in all procedures (range 8–12). Immediately after the pulses were delivered, tumor
tissue became pale and ischemic ([Fig. 2 ]). Median procedure time from the patients were sedated to end of the procedure was
35 minutes (range 28–55 minutes). All patients were discharged approximately 1 hour
after the treatment. All procedures were successful and no complications have been
observed in relation to the procedures. For procedure-related characteristics, see
[Table 2 ].
Fig. 2 Images of a T2 tumor in the sigmoid colon before and immediately after treatment with
calcium electroporation. Calcium was injected and thereafter pulses were applied consecutively
to cover the tumor volume. After treatment, the tumor tissue became ischemic, whereas
normal tissue was less affected by the treatment.
Table 2
Procedure characteristics.
Patient
Endoscopy
Treatment
Calcium chloride (mL)
Series of pulses
Treated tumor surface
Treatment duration
Comments
1
1
1
3
5
> 25 %
55 min
Tumor not passable with the endoscope
1
2
Insufficient bowel preparation
2
1
1
5
3
> 25 %
28 min
Tumor not passable with the endoscope
2
2
Insufficient bowel preparation
3
1
1
10
7
> 75 %
30 min
3
2
2
11
6
100 %
30 min
4
1
1
11
10
> 50 %
50 min
5
1
1
13
8
> 75 %
28 min
5
2
2
13
8
100 %
25 min
5
3
3
13
15
100 %
50 min
6
1
1
13
8
> 75 %
45 min
6
2
2
13
8
100 %
40 min
6
3
No visible tumor
Adverse events
No procedure-related serious AEs were reported. In two cases (patients no. 1 and 6),
patients experienced fever and general malaise within the first 24 to 48 hours after
treatment. In both cases, spontaneous recovery was seen after 24 hours.
Pain score
Pain in relation to the study treatment and at follow-up was evaluated. A median NRS
score of 0 (range 0–1) was reported at all time points (baseline, Day 1, Day 7, Week
4 and Week 8).
Response to treatment
After the initial treatment, five patients were followed with an endoscopic procedure,
and one patient (no. 4) was deemed unsuitable for an additional procedure due to comorbidity
and tumor progression. At follow-up the tumor was evaluated by inspection. In four
cases, PR was seen, with necrotic tumor tissue and fibrin. Patient no. 6 had clinical
CR, with fibrin at the previous tumor site with no visible residual tumor tissue ([Fig. 3 ]).
Fig. 3 Endoscopic images from a 62-year-old man with a rectal tumor. a Baseline image just before the initial treatment with calcium electroporation. b Follow-up 12 weeks after treatment showing fibrin and no visible tumor. c Follow-up 4 months after treatment showing normalization of treatment area.
Symptom relief
Of the six patients, five reported symptom relief after study treatment. Patient no. 1
with sigmoid colon cancer suffered from bleeding, pain, and obstruction prior to treatment
and 2 days after treatment, the patient reported reduced pain, bleeding ceased and
the obstruction was partially relieved. Five patients with a rectal tumor all suffered
from stenosis. Of these, four patients reported partial relief of obstruction a few
days after the initial treatment. Of the five patients with a rectal tumor, three
suffered from malignant bleeding. Of these, two patients (no. 1 and 3) reported that
the bleeding ceased within a few days after treatment. One patient (no. 4) did not
report symptom relief after treatment.
Radiologic evaluation
All patients were evaluated with CT scans and metastases were evaluated according
to RECIST 1.1 criteria. Patients with rectal cancer were also evaluated with MRI of
the primary tumor.
MRI was performed on five patients. In three patients, MRI found reduced tumor size
of 1, 1.5 and 2 cm, respectively. In one patient, tumor size increased by 1 cm. Patient
no. 6 was unable to cooperate for a baseline MRI; however, an MRI was performed at
the final follow-up visit. This patient had macroscopic CR and MRI showed a residual
tumor lesion consisting of primarily fibrosis and edema.
RECIST 1.1 evaluation of metastasis found stable disease in three patients and progression
of metastasis in two patients ([Table 3 ]). Complete regression of lung metastasis and PR of liver metastasis and rectal tumor
were found in patient no. 6 ([Fig. 4 ]).
Table 3
CT scans with evaluation of metastasis according to RECIST criteria.
Patient
Additional treatment
4 weeks
8 weeks
12 weeks
6 months
1
Capecitabine
SD
SD
2
SD
PD
3
SD
SD
SD
4
PD
5
FOLFIRI
SD
SD
SD
6
Capecitabine + bevacizumab
PR
PR (liver)/CR (lung)
CT, computed tomography; RECIST, Response Evaluation Criteria in Solid Tumours; FOLFIRI,
folinic acid, fluorouracil, irinotecan; SD, stable disease; PD, progressive disease;
PR, partial response; CR, complete response.
Fig. 4 CT scans at baseline and 12-week follow-up in patient no. 6 showing regression of
liver metastasis. The patient had complete regression of lung metastasis and partial
response of liver metastasis. The patient received systemic chemotherapy during the
period from calcium electroporation to follow-up.
Cell-free DNA
The concentration of cfDNA in alleles per mL is shown in Supplementary 2 . Based on the visualization, there are no clear patterns of changes in cfDNA concentration
over time.
Pathological evaluation
Qualitative pathological evaluation
Baseline biopsies were compared with follow-up biopsies by a gastrointestinal pathologist.
In patients no. 1, 2, 3 and 5, no clear changes in tissue morphology were seen. In
patient no. 6, baseline samples showed adenocarcinoma, ulcerous tissue and granulation
tissue. At follow-up, multiple biopsies were collected. Follow-up biopsies after 12
weeks showed granulation tissue and ulcerous tissue and no residual adenocarcinoma.
At 4-month follow-up biopsies, only granulation tissue persisted. Patient no. 4 had
no follow-up biopsies collected.
Quantitative analysis of CD3– and CD8-positive cells
The densities of CD3 and CD8 in each tissue compartment of the biopsies are shown
in Supplementary 3 and Supplementary 4 . The visualization of each individual patient shows that CD3 and CD8 density follow
the same trend across tissue compartments. Overall, based on the visualization, no
clear trend of changes in the density appeared over time.
PD-L1 evaluation
PD-L1-positive cells were seen in all baseline samples and for all patients the expression
was primarily located in the immune cells. In patients no. 1 and 3, few positive cells
were present, while patients no. 4 and 5 had a moderate number of positive cells and
only in patient no. 2 a high number of PD-L1-positive cells were present. Patient
no. 4 had no follow-up biopsies collected. Patient no. 6 had no residual tumor cells
in the follow-up samples and was excluded from analysis. No clear trend was found
when we compared baseline samples with follow-up samples.
Discussion
This study is the first-in-human clinical study to investigate calcium electroporation
for colorectal cancer and we found that the treatment is safe and feasible. Furthermore,
clinical response and symptom relief are indicated. An endoscopic device (EndoVE)
enabled electroporation-based treatments in the gastrointestinal tract. The EndoVE
device has been proven safe in clinical trials investigating electrochemotherapy with
bleomycin for esophageal cancer and advanced colorectal cancer [20 ]
[21 ]
[22 ]
[23 ].
Endoscopic calcium electroporation was found to be a safe and feasible outpatient
procedure, with limited side effects. A total of six patients were included in the
study and a total of 10 procedures with calcium electroporation were performed. The
patients reported symptoms including pain, malignant bleeding and stenosis before
entering the protocol. After the initial procedure with calcium electroporation, five
patients reported symptom relief. In all cases, palliative relief was achieved within
a few days.
Treatment response was evaluated through imaging and biopsies. Evaluation found stable
disease in three patients and progression in two. The final patient was treated with
calcium electroporation followed by systemic chemotherapy, and CT scans showed complete
regression of lung metastasis and partial response in liver metastasis. In addition,
pathological evaluation of biopsies from follow-up colonoscopies found no residual
adenocarcinoma after calcium electroporation.
Of the included patients, three suffered from hemorrhage from their malignant tumors
prior to the treatment. All patients reported symptom relief within a few days. These
findings correlate with previous evidence showing an anti-vascular effect of calcium
electroporation. A previous study found that calcium electroporation suppressed the
ability of the endothelial cells to migrate and form capillary-like structures [24 ]. Interestingly, evidence suggests that calcium electroporation induces ATP loss
and necrosis of cancer cells, whereas normal tissue tolerates the treatment [2 ]. This correlates with the findings of this study, showing pale and ischemic tumor
tissue immediately after the electrical pulses were applied, whereas normal tissue
was less affected by the treatment.
The study was limited by the small number of patients. Furthermore, the group was
heterogenic as these fragile patients could not attend all follow-up visits. Histopathological
examination of immune cell infiltration and necrosis was performed, and no statistically
significant signal in tumor-related immune infiltration or in tissue morphology was
seen. In addition, a number of patients received systemic chemotherapy before or after
calcium electroporation, and as such, the isolated effects of calcium electroporation
are difficult to determine. The reported tumor responses may, in fact, be due to a
multimodal treatment rather than calcium electroporation alone.
This first-in-human clinical trial found calcium electroporation to be an efficient
palliative treatment option for this patient group. The treatment was performed as
an outpatient procedure, and in most cases, an enema was sufficient as bowel preparation.
Calcium electroporation offers an alternative treatment where symptom palliation is
needed and can be offered in addition to chemotherapy. The procedure is, however,
limited as treatment is dependent on the endoscopic device to reach and cover the
entire tumor surface area, which is not always possible.
Previous studies have found endoscopic electrochemotherapy with systemically administered
bleomycin to be a safe and feasible procedure with promising results [20 ]
[21 ]
[22 ]. However, the use of bleomycin is limited due to risk of interstitial pulmonary
fibrosis. In contrast, calcium chloride is injected locally and may be associated
with a lower risk of side effects. Based on the current data, we expect electrochemotherapy
and calcium electroporation to have comparable anticancer effects [7 ]
[8 ]
[11 ]
[12 ]
[23 ]; however, there are currently no studies comparing endoscopic electrochemotherapy
with calcium electroporation for colorectal cancer.
