Prophylactic radiotherapy to prevent procedure-tract metastases

Prophylactic irradiation of tracts in patients with malignant pleural mesothelioma: A systematic review and meta-analysis of randomized trials

INTRODUCTION

The role of prophylactic irradiation of tracts (PIT) to prevent tumor seeding at the site of a diagnostic or therapeutic intervention in patients with malignant pleural mesothelioma (MPM) is controversial. This study aimed to determine the efficacy of PITs in preventing procedure tract metastases (PTM) after a chest wall procedure in MPM.

MATERIALS AND METHODS

We searched various databases from inception date to April 2020 for randomized controlled trials (RCTs) comparing PIT with no PIT in patients who had a chest wall procedure for MPM. We assessed the risk of bias of individual RCT using the RoB2 tool. The primary outcome was the occurrence of PTM. Meta-analysis was performed using random-effects model. We employed the GRADE approach to assess the certainty of the evidence.

RESULTS

We identified five RCTs including 737 patients. Two RCTs had a low risk of bias. PIT was associated with a significant reduction in the odds of PTM (odd ratio, 0.55; 95 % confidence interval, 0.32 to 0.95; P-value = 0.03; I² = 13 %; GRADE: moderate certainty). One RCT reported no difference in overall survival outcome with the use of PIT. None of the RCTs performed subgroup analyses. Sensitivity analyses showed similar results when limited to RCTs with low risk of bias.

CONCLUSION

PIT significantly reduces the occurrence of PTM in patients with MPM who had a diagnostic or therapeutic chest wall procedure.

Novel therapies for malignant pleural mesothelioma

Malignant pleural mesothelioma is a rare cancer that is typically associated with exposure to asbestos. Patients with malignant pleural mesothelioma have poor outcomes with suboptimal therapeutic options and currently no treatment is curative. The standard frontline treatment, cisplatin plus pemetrexed chemotherapy, has only short and insufficient efficacy, and no validated treatment beyond first-line therapy is available. New therapeutic strategies are therefore needed. The addition of bevacizumab (an anti-VEGF antibody) combined with cisplatin plus pemetrexed has shown some promise. However, immunotherapy, especially immune checkpoint inhibitors, has generated a lot of excitement because of data suggesting the potential value of immune checkpoint inhibitors for patients who have failed chemotherapy. In this Review, we describe immune checkpoint inhibitors, other immunotherapies, targeted therapies, or combinations of novel drugs being investigated in malignant pleural mesothelioma, as well as the issues surrounding the selection of the best candidates for these treatments.

Is there a role for prophylactic radiotherapy to intervention tract sites in patients with malignant pleural mesothelioma?

Malignant pleural mesothelioma has a high morbidity and poor prognosis. Most patients undergo invasive pleural interventions to either facilitate diagnosis and/or alleviate symptoms from malignant pleural effusion. Procedure tract metastasis (PTM) are a well-known complication of pleural procedures in mesothelioma and there has been longstanding debate regarding the role of prophylactic irradiation of tracts in preventing them. This review summarises the existing evidence surrounding this controversial topic. Despite initial discrepancies amongst the results of 3 small, historical trials regarding the efficacy of prophylactic radiotherapy in mesothelioma, two large randomised-control trials have recently provided more clarity. The SMART trial, which randomised over 200 patients, found no benefit of prophylactic radiotherapy in reducing PTM incidence in their primary analysis, with a number needed to treat (NNT) of 25.1 to prevent a single painful PTM. Additionally, there was no benefit in terms of symptomology, health-related quality of life parameters or cost-effectiveness. This is supported by the preliminary results of the Prophylactic Irradiation of Tracts in Patients with Pleural Mesothelioma (PIT) trial, which randomised 375 patients and also found no evidence that prophylactic radiotherapy reduced PTM incidence, although the full results are still awaited. Combined analysis of these trials is planned, which will help clarify whether specific subpopulations may derive benefit from prophylactic radiotherapy, such as patients not receiving chemotherapy. Based on the currently available evidence there is no role for routine delivery of prophylactic radiotherapy to prevent PTM in mesothelioma. Instead holistic and vigilant follow-up of patients is recommended, aiming for adequate palliation of symptoms and support for patients. Should painful nodules develop these can be effectively treated with subsequent palliative radiotherapy. After years of uncertainty and debate, recent international guidelines have consistently advised against the use of prophylactic irradiation of tracts based on contemporary high-quality evidence.

Prophylactic radiotherapy for procedure tract metastases in mesothelioma: a review

PURPOSE OF REVIEW

Malignant pleural mesothelioma is an aggressive malignancy with a very poor prognosis. The majority of patients require pleural procedures for diagnostic or fluid management purposes. Damage to the pleura during these procedures can lead to procedure tract metastases (PTMs), with increasing risk from larger interventions. Prophylactic radiotherapy to these sites is a controversial topic with conflicting results from trial data. In this review, we summarize the recent evidence.

RECENT FINDINGS

Four RCTs have been published on this topic, with another in follow-up. The earliest, from a cohort of 40 patients, strongly advocated the use of prophylactic radiotherapy. More recent trials, most notably the Surgical and large bore procedures in Malignant pleural mesothelioma And Radiotherapy Trial (SMART) (which randomized over 200 patients) did not demonstrate any benefit, especially when patient report symptoms and cost-effectiveness are considered. Certain subgroups demand further investigation, such as those not receiving systematic chemotherapy or with surgical intervention sites. The soon to be published Prophylactic Irradiation of Tracts (PIT) trial may help to further clarify best practice.

SUMMARY

Recent studies have shown that prophylactic radiotherapy should not be routinely used to prevent PTMs in mesothelioma. Instead patients should undergo careful clinical follow-up to ensure PTMs are identified and treated promptly to minimize symptoms.

[Anti-tumor immunotherapy in malignant pleural mesothelioma]

INTRODUCTION

Malignant pleural mesothelioma (MPM) is a quite rare cancer, but with increasing incidence, that is usually induced by previous asbestos exposure. Its prognosis is poor and there is no validated curative therapy to date. Surgery of MPM, done only by few expert teams within a multimodal treatment is of limited and still disputed value. The standard treatment of MPM, relying on first-line chemotherapy by combined cisplatin-pemetrexed is often poorly effective, even if combination with bevacizumab anti-VEGF antibodies has slightly improved the results. Moreover, no second line treatment is recommended in case of failure of this chemotherapy. Therefore, the search of new therapies or strategies is crucial and the recruitment of patients in clinical trials is highly encouraged.

BACKGROUND

Among the treatments under investigation, various anti-tumour immunotherapies, in particular immune checkpoints inhibitors (ICI), currently exhibit the most promising preliminary results. First data from the phase II, randomized "IFCT MAPS-2", recently presented during the 2017 ASCO meeting, confirmed the value of ICI in MPM patients in cases of chemotherapy failure.

OUTLOOK AND CONCLUSIONS

However, several exciting immunotherapies other than ICI are presently being evaluated in MPM and are reported in this article. Moreover, many questions still need to be answered about immunotherapy: what is its potential value as first line treatment? How to target the best candidates for these treatments? Which combinations between immunotherapy and standard chemotherapy, targeted therapies, surgery or radiotherapy? Finally, it is now essential that every clinician has sufficient knowledge about the possible toxicities of immunotherapy.

Proteasome stress sensitizes malignant pleural mesothelioma cells to bortezomib-induced apoptosis

Based on promising results in preclinical models, clinical trials have been performed to evaluate the efficacy of the first-in-class proteasome inhibitor bortezomib towards malignant pleural mesothelioma (MPM), an aggressive cancer arising from the mesothelium of the serous cavities following exposure to asbestos. Unexpectedly, only minimal therapeutic benefits were observed, thus implicating that MPM harbors inherent resistance mechanisms. Identifying the molecular bases of this primary resistance is crucial to develop novel pharmacologic strategies aimed at increasing the vulnerability of MPM to bortezomib. Therefore, we assessed a panel of four human MPM lines with different sensitivity to bortezomib, for functional proteasome activity and levels of free and polymerized ubiquitin. We found that highly sensitive MPM lines display lower proteasome activity than more bortezomib-resistant clones, suggesting that reduced proteasomal capacity might contribute to the intrinsic susceptibility of mesothelioma cells to proteasome inhibitors-induced apoptosis. Moreover, MPM equipped with fewer active proteasomes accumulated polyubiquitinated proteins, at the expense of free ubiquitin, a condition known as proteasome stress, which lowers the cellular apoptotic threshold and sensitizes mesothelioma cells to bortezomib-induced toxicity as shown herein. Taken together, our data suggest that an unfavorable load-versus-capacity balance represents a critical determinant of primary apoptotic sensitivity to bortezomib in MPM.

Radiotherapy for the treatment of malignant pleural mesothelioma

Malignant pleural mesothelioma is an aggressive disease that continues to be associated with poor outcomes. Although, traditionally this disease is considered to be resistant to radiotherapy, more recent evidence suggests that radiotherapy can produce positive outcomes. Over the past 15 years, the development of new, highly conformal radiotherapy techniques, such as intensity-modulated radiation therapy (IMRT), has enabled investigators to optimise the delivery of high-dose radiotherapy to the whole of the hemithorax. Prospective single-arm trials have shown that the median survival of patients who have completed high-dose hemithoracic radiotherapy after extrapleural pneumonectomy could reach 23·9-39·4 months independent of the chemotherapeutic response, suggesting that IMRT could potentially have an intrinsic benefit to this subset of patients. These observations have led to a change in practice, with the introduction of adjuvant pleural IMRT after pleurectomy-decortication and the development of induction-accelerated hemithoracic IMRT followed by extrapleural pneumonectomy. This Review focuses on recent observations on the role of radiotherapy in the treatment of malignant pleural mesothelioma, with particular emphasis on the results of clinical trials that evaluate the role of high-dose hemithoracic radiotherapy.