Photodynamic therapy of malignant mesothelioma of pleura.

T. Warloel, H. Heyerdahll, Q. Peng2, J. H0iel, E. Normannl,
0. Solheim3, J. Moan2, K.-E. Gierckskyl.

Departments of Surgical Oncologyl and Oncology3, The Norwegian Radium Hospital
Departments of Biophysics2, Institute for Cancer Research
Montebello, 0310 Oslo, Norway.

ABSTRACT

Nine patients with malignant pleural mesothelioma underwent extensive surgery followed by intra-operative 
photodynamic therapy. 2 mg/kg Photofrin was given 48 hours prior to surgery. The thoracic cavity and 
eventual remaining lung were exposed to 15-30 Joules/cm2 of 630 nm laser light. Tumour tissue was analysed 
by microscopic photometrical techniques. Five patients with mixed or epitheloid tumours with fluorescence 
intensity >100 grey leveVpixel seemed to benefit from the given therapy. One patient was free of disease 18 
months after treatment. Two patients were treated for metastasis after 12 months with no sign of intrathoracic 
recurrency. Both are still alive, one without further sign of disease 32 months after initial treatment. Two 
patients presented generalized disease after 9 and 13 months and intrathoracic recurrency several months later. 
Two patients with poorly differentiated tumours and 2 patients with moderate to highly differentiated tumours, 
but with fluorescence intensity <100 grey level/pixel, presented recurrencies after 4 months. PDT-efficiency 
seems to be predicted by the intensity and distribution of drug-induced fluorescence in tumour tissue. PDT 
may enhance the possibility to achieve complete local tumour control after excision. Multimodal therapeutic 
approach of local and systemic disease seems mandatory to further improve survival.

Keywords: Malignant pleural mesothelioma, surgery, intraoperative photodynamic therapy, Photofrin, 
fluorescence microscopy analysis, PDT-efficiency predictability.

1. INTRODUCTION

Malignant mesothelioma is an almost invariably fatal cancer disease that occurs on serosal surfaces of the 
body. Induction of malignant pleural mesothelioma is most commonly caused by exposure to asbestos fibers, 
followed by a latency period of 20-40 years before appearance of symptomsl. There is no standard therapy for 
such disease. Radiotherapy and chemotherapy have little effect in the treatment of malignant pleural 
mesothelioma2~4 and in some European countries surgery is considered to be even less effective.

Photodynamic therapy (PDT) is an investigative cancer treatment modality5-7 that has been under 
development during the last decades. The basis of this therapy involves the in situ activation of a 
photosensitiser accumulated in tumour and normal tissue by visible light, causing cell death8~10. The 
specificity of the PDT-effect correlates with the biodistribulion of the photosensitising substance8. Porfimer 
sodium, Photofrin, is the most widely used photosensitiser in current clinical trials. PDT is mainly a local 
treatment and has the potential, as an adjuvant therapy, to enlarge the surgical margins and may thereby 
transform an incomplete surgical resection due to anatomic or structural limitations, to a complete local 
tumour eradication. PDT using Photofrin has been shown to be effective in human mesothelium grown as 
xenografts in rodentsll l2 and in a few humans cases using Photofrinl3 or a chlorin photosensitiserl4.

2. MATERIAL AND METHODS

Patients with biopsy-proven malignant mesothelioma as confirmed by immunohistochemistry and/or electron 
microscopy and tumour mass confined to one hemithorax were evaluated for surgical intervention combined 
with intraoperative PDT. Patients were examined by CT-scan to exclude contralateral or extrathoracic 
manifestations. Consent for this experimental therapeutic modality was obtained from all patients after 
appropriate information. Photofrin, (Lederle, American Cyanamid, NY, USA) was dissolved in sterile 5% 
dextrosis and intravenously administrated at a dose of 2 mg/kg bodyweight 48 hours prior to surgery. Surgical 
intervention by thoracotomy and a tumour-debulking procedure of gross tumour to less than 5 mm thickness 
was initially performed. The thoracic cavity and eventual remaining lung surfaces were intra-operatively 
exposed to 630 nm light

pulsed at 10 kHz from a copper vapour pumped dye laser (Cu15A and DL30, Oxford Lasers, Oxford, UK). 
Light was transmitted through a single quarts fiber, either flat-cut or equipped with a sphere at the distal end 
(PDT systems, Santa Barbara, CA, USA). A combined cooling/ light dispersing unit containing either glycerol 
or dispersing medium was used to prevent destruction of the fiber tip and thus to take advantage of the full 
output power from the laserl5. With this system an approximately spherical light distribution was obtained. 
Total power out from the light delivery system was measured by an intergrating sphere power meter (Model 
2015, PDT Systems, Santa Barbara, CA, USA). Light dose (fluence) delivered to the tissue surface was 
estimated by calculation of the primary irradiance. The intended light fluence was 15-30 Joules/cm2. Tumour 
biopsies were removed prior to and after light irradiation for studies by means of fluorescence microscopy. By 
this technique, the localization pattern of porphyrin fluorescence in the tissue sections could be directly 
observed, giving a measure of biodistribution and tissue concentration of the photosensitising drug. After 
surgical removal, samples were immediately immersed in liquid nitrogen and the tissue sections were cut to a 
thickness of 8 mm using a cryostat microtome. The same frozen sections were subsequently stained by routine 
H&E staining for histological identification. Fluorescence microscopy was carried out with an Axioplan 
microscope (Zeiss, Elena, Germany). The filter combination used for the detection of the porphyrin 
fluorescence consisted of an 390-440 nm excitation filter, a 460 nm beam splitter and a > 600 nm emission 
filter. The fluorescence images were performed by a CCD camera (Astromed CCD 3200, Cambridge, UK).

Nine patients (2 females and 7 males aged from 41 to 70 years) were included in this study. Five patients had a 
history of exposure to asbestos (no. 3-7), the other 4 had no known exposure to asbestos. In 4 patients (no. 2-5) 
the disease had been diagnosed 6-12 months prior to the start of this study. These patients had earlier received 
chemotherapy and presented signs of progressive disease at the time of surgery. For the other patients the 
inclusion were done at time of diagnosis. Specimens to establish histological verification were generally 
obtained by needle-biopsies. In 2 patients an operative procedure was neccessary to obtain representative 
tumour material. Patient no. 3 had a known implantation metastasis in the scar tissue after former diagnostic 
thoracotomi. Diagnosis based upon needle-biopsies often predicted a histopathological type of the lesions 
which differed from the final ones established postoperatively. There were epitheloid type lesion in 6 patients 
and mixed type in 3 patients. The degree of differentiation varied from I-III. Fluorescence data were 
established postoperatively (Table 1).

, The surgical procedure was done by thoracotomy, right-sided in 6 patients and left-sided in 3. The surgical 
aim was to obtainl radical excision of tumour. Extrapleural pneumonectomy (EPP) was performed in 5 
patients. Pleurectomy, lobectomy and partial decortication of remaining lung tissue were done in 3 patients. 
Pleural resection and decortication were performed in one patient. In 7 patients the diaphragm was resected 
and in 3 of these, due to large tumour masses in the costophrenic sulcus, a complete ipsilateral removal of the 
diaphragm was performed. In 6 patients pericardial resection was done. (Table 2).

Intra-operative PDT was then performed, shielding the heart and eventually the liver/spleen from light 
exposure with a sheet of aluminium within sponges. The light intensity varied considerably over the treated 
surface because of the geometry of the thoracic cavity. The light fluence was gradually increased from 15 to 30 
Joules/cm2 throughout the series, the determined fluence was considered to be a minimum dose in all areas 
exposed. (Patient no. 4 received 15 J/cm2, no. 2, 5 and 8 were given 20 J/cm2 and the rest 30 J/cm2). A 
computerized light dosage calculation program correlated to pre-operative CT measurements was established, 
but due to changes of intrathoracic geometry during operation, recalculations demonstrated deviations between 
the intended and the given light fluence. Limited areas received less light than given above. Since only one 
laser and a single light delivery system were available, the light diffuser was moved into a maximum of 20 
different positions to cover the entire resectional area. The time of light exposure varied from 2,5 and 9.5 
hours, average 6,3 hours, and the duration of operation therefore were of unusual lenght (range: 10-20 hours, 
mean 17 hours).

Extemal ionizing radiation of the chest wall including all scars after thoracotomy and accessory entrances was 
performed postoperatively in order to prevent occurrence of metastasis (10-15 MW, 10-20 fractions, 30-40 
Gy). All patients were followedup postoperatively by serial computerized tomography scans every 3 months.

3. RESULTS

There was no perioperative mortality. One patient presented a surgical complication by persisting leakage from 
ductus thoracicus, the patient therefore was reoperated after 21 days without further complications. One 
incidence of skin photosensitivity was observed, this consisted of localized skin necrosis and was treated by 
split-skin grafting. The event occured in an area close to the thoracotomy and was caused by the light from 
lamps in the surgical theatre. One patient developed an acute respiratory distress syndrome due to Pseudomona 
aeroginousa infection. Short transient periods of cardiac arythmia related

to statural changes were seen during the first 2 weeks in patients who had undergone complete diaphragmatic 
(and pericardial) resection. This was surprisingly well tolerated by the patients. Hyperthermia and chest pain 
was observed during the first weeks. The patients did not develop neither neural and vascular alterations nor 
bronchial suture insufficiency. Patients were discharged from the hospital from 10 to 90 days postoperatively, 
the average hospitalization period was 25 days.

The patients were controlled by CT-scans every 3 months. In one patient (no. 1) no sign of recurrency has been 
found 18 months after treatment. One patient (no. 2) presented after 12 months an implantation metastasis in 
the thoracic wall. The tumour was located far from the incision, in an area of multiple punctures for 
evacuation of pleural effusion prior to operation. The metastasis was resected by thoracotomy and there was no 
sign of intrathoracic tumour. Additional radiotherapy towards the affected area was given post-operatively. 
The patient has since been free of disease for 32 months after the initial treatment. These two long term 
disease-free patienes had initially presented highly differentiated tumours with homogenious distribution of 
high intensity of the fluorescent photosensitiser.

Patient no. 6 presented after 12 months a retroperitoneal metastasis located around the aorta, vena cava 
inferior and portal vein. The tumour was resected and PDT again performed with light fluence of 50 
Joules/cm2. The fluorescence intensity of the initial pleural tumour and the metastasis was 104 and 43 grey 
level per pixel, respectively (Table 1). At control 3 months later multiple metastases were detected within the 
abdomen and mediastinum, as well as in other areas distant from treated tumour sites.

Two patients (no. 4 and 5) presented multiple metastases 9 and 13 months after treatment. These metastases 
were initially located within the abdomen and controlateral hemithorax and were 3 months later found within 
the treated hemithorax. Both patients had a long history of known mesothelioma and large tumour masses at 
time of actual treatmenL Tumours were highly differentiated and showed fluorescence intensities ranging from 
176 to 248 grey level per pixel. Patient no. 3 developed recurrency after 3 months and distant metastases 5 
months after treatment. The history of disease, size of tumour and its level of fluorescence intensity were 
identical as for the above mentionned patienes, only the differentiation grade was lower.

Three patients (no. 7, 8 and 9) presented generalized disease 4-5 months after treatment, showing 
manifestations within the treated hemithorax as well as contralateral and intraabdominal metastases. In two of 
those patients the tumour had low fluorescence intensity and in the third patient, who had a tumour of mixed 
type with differentiation grade I, the fluorescence was of high intensity but unevenly distributed within the 
tumour tissue.
!
Prior to treatment all patients complained of chest pain. Most patienes had pleural effusion that was frequently 
drained. During the first week after treatrnent patients had a severe chest pain, this was reduced during the 
following months and the surviving persons do not complain of any particular chest pain. No pleural drainage 
was to be performed in a late postoperative period for any patienL

4. DISCUSSION

Single modality therapeutic management has yielded few long-term survivors in malignant pleural 
mesothelioma. The role of surgery is generally considered to be limited. Pleurectomy/decortication is an 
incomplete tumour-debulking procedure and therefore ineffective as a single treatment with curative aim. 
Extensive surgery by EPP has been advocated as a theoretically more attractive operation because it may allow 
a radical excision, but only a minority of patients with mesothelioma qualify for this operation and it carries a 
higher risk. Studies have shown that patients undergoing EPP have a greater tendency towards development of 
distant diseasel6. The therapeutic challenge is two-fold, effective treatment regimens for malignant 
mesothelioma must address the problem of systemic disease as well in order to obtain local and systemic 
control of the malignancy. Combined treatment modality appears to offer some promise in this otherwise 
rapidly fatal diseasel7.

The impact of the presented method in a small and heterogeneous patient group is difficult to evaluate. 
However, patients no. 2 and 6 reoperated a year after initial treatment were completely free from tumour 
within the thoracic cavity. During the follow-up, in 3 patienes distant metastases.were seen prior to recurrency 
within the treated hemithorax. Such results of relatively long-lasting local control were obtained in patients 
undergoing various surgical procedures with low mortality/morbidity. The tumours of these patienes presented 
photosensitizer Suorescence of even distribution and of high intensity. Patients with tumours of 
inhomogenious (related to the differentiation grade) and low fluorescence intensities showed

rapid recurrency and metastases. Patient no. 6, presenting a relatively high nuorescence intensity of the initial 
tumour and a significantly lower intensity in the metastatic tumour, showed generalized malignancy only 3 
months after retreatment.

An approach by thoracoscopic PDT13 was considered not useful in these patients all of whom presented 
tumour masses of large size located in the costophrenic sulcus. CT scans did not offer sufficent accuracy to 
evaluate tumour thickness, especially in the costophrenic sulcus. We experienced improved surgical radicality 
as well as improved access for light exposure in this area by doing complete diaphragmatic resection.

As a conclusion we present the hypothesis that associated PDT-treatment has a clinical effect and that 
predictability of PDT-efficiency seem to be related to the distribution and intensity of the fluorescence induced 
by the photosensitiser in tumour (Table 1). The PDT-effect may enhance the potential to complete local 
tumour eradication even in the case of less aggressive surgical debulking procedure. However, as clearly 
visualized in this study a multimodal therapeutic approach addressing to the systemic disease seems necessary 
to further improve survival.

5. ACKNOWLEDGMENT

This study was finacially supported by The Norwegian Cancer Society. Photosensitiser and some of the 
technical equipment was a gift from Lederle, American Cyanamid.

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