Is Prophylactic Irradiation After Chest Wall Procedure Beneficial in Mesothelioma?

Patients with malignant pleural mesothelioma (MPM) who received prophylactic irradiation after a chest wall procedure did not clinically benefit, according to an open-label, multicenter, phase III clinical trial. The trial results published in the Journal of Clinical Oncology suggest that prophylactic irradiation is not warranted in patients with MPM after a chest wall procedure.

“Prophylactic irradiation in MPM has slowly fallen out of favor in the United States and is less commonly used as more studies have been published showing lack of benefit,” Jing Zeng, MD, a medical oncologist with Seattle Cancer Care Alliance, told Cancer Network. For example, she said, the current National Comprehensive Cancer Network guidelines for mesothelioma recommend against routine prophylactic radiation. “[The trial] appears to reaffirm findings from earlier, smaller trials conducted on the same topic, in the setting of more modern treatments such as a high rate of platinum doublet chemotherapy,” she said.

The current trial included 375 patients with MPM from 54 hospitals in the United Kingdom who had undergone a chest wall procedure. Patients were randomized to receive either prophylactic radiotherapy (within 42 days of the chest wall procedure) or no prophylactic radiotherapy. Using a single electron field adapted to maximize coverage of the tract from skin surface to pleura, prophylactic radiotherapy was given at a dose of 21 Gy in 3 fractions once daily over 3 consecutive working days. The primary outcome was incidence of chest wall metastases at 6 months.

At 6 months, 6 of 186 patients (3.2%) in the prophylactic radiotherapy group had chest wall metastases compared with 10 of 189 patients (5.3%) in the group with no prophylactic radiotherapy. The difference was not significant (odds ratio, 0.60; 95% CI, 0.17–1.86; P = .44). The cumulative incidence over 24 months was 46 chest wall metastases, as seen in 17 of 186 patients in the prophylactic radiotherapy group and 29 of 189 patients in the no prophylactic radiotherapy group. The difference also lacked statistical significance (hazard ratio, 0.57; 95% CI, 0.31–1.03; P =. 06).

Although the cumulative incidence at 24 months approached statistical significance, Zeng explained that the overall disease control rate in mesothelioma remains suboptimal, with the 1-year overall survival rate being less than 50%. “Therefore, very few patients are likely to be alive and disease-free at 2 years to benefit from a small potential benefit in local control at the instrument tract,” she said. 

The most frequent radiotherapy-related adverse event among patients in the prophylactic radiotherapy group was skin toxicity. Approximately half (51.6%) had grade 1 radiation dermatitis and 10.2% had grade 2 radiation dermatitis; 1 patient (0.5%) had grade 3 radiation dermatitis. By contrast, only 1 patient in the no prophylactic radiotherapy group reported radiation dermatitis, which was grade 2.

Zeng agreed with the study authors’ conclusion that prophylactic radiation should not be routinely offered to all patients with MPM. “Right now, overall survival rates are still suboptimal for patients with mesothelioma, with most patients developing disease progression at multiple sites, all of which can be painful. Therefore, prophylactic radiation to one site, even if it decreased recurrence at that one site, is unlikely to impact a patient’s overall quality of life,” she said.