Routine Prophylactic vs Deferred Radiotherapy for Procedure-Tract Metastases in Malignant Pleural Mesothelioma
Prophylactic radiotherapy after surgery and large-bore pleural procedures did not result in significant reduction in the incidence of procedure-tract metastases in malignant pleural mesothelioma, according to the UK phase III SMART trial reported by Clive et al in The Lancet Oncology.
Study Details
In this open-label trial, 203 patients from 22 UK sites who had undergone large-bore pleural interventions within 35 days prior to recruitment were randomized between December 2011 and August 2014 to receive immediate radiotherapy at 21 Gy in 3 fractions within 42 days of the intervention (n = 102) or deferred radiotherapy at the same dose given within 35 days of diagnosis of procedure-tract metastases (n = 101).
The primary outcome measure was the incidence of procedure-tract metastases within 7 cm of the pleural intervention site within 12 months from randomization in the intent-to-treat population.
Incidence of Procedure-Tract Metastases
Overall, 99 of 102 patients in the immediate-radiotherapy group received radiotherapy as assigned, and 9 of 16 patients in the deferred-radiotherapy group who developed procedure-tract metastases received radiotherapy according to study protocol. The incidence of procedure-tract metastases was 9% (9 patients) in the immediate-radiotherapy group vs 16% (16 patients) in the deferred-radiotherapy group (odds ratio = 0.51, P = .14).
In a subgroup analysis, there was some evidence of preventive benefit among 71 immediate-radiotherapy patients with epithelioid-only tumor subtype (hazard ratio [HR] = 0.35, P = .057) and among 46 patients who did not receive chemotherapy after trial entry (HR = 0.16, P = .021)
Toxicity
The only serious adverse event related to procedure-tract metastases or radiotherapy was painful procedure-tract metastases within the radiotherapy field, which required hospitalization for symptom control in one patient in the immediate-radiotherapy group. Among 92 evaluable patients in the immediate-radiotherapy group, common adverse events within 3 months of radiotherapy included skin toxicity (grade 1 in 54% and grade 2 in 4%, no grade 3 or 4) and tiredness/lethargy (39%). Grade 1 skin toxicity and tiredness/lethargy were seen in 2 of 5 evaluable deferred-radiotherapy patients.
The investigators concluded: “Routine use of prophylactic radiotherapy in all patients with mesothelioma after large-bore thoracic interventions is not justified.”
The study was funded by the Research for Patient Benefit Programme from the UK National Institute for Health Research.
Nick A. Maskell, DM, of the University of Bristol, United Kingdom, is the corresponding author of The Lancet Oncology article.
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