Combined irradiation and targeted therapy or immune checkpoint blockade in brain metastases: toxicities and efficacy

Background

Targeted therapies (TT) and immune checkpoint inhibitors (ICI) are currently modifying the landscape of metastatic cancer management and are increasingly used over the course of many cancers treatment. They allow long-term survival with controlled extra-cerebral disease, contributing to the increasing incidence of brain metastases (BMs). Radiation therapy remains the cornerstone of BMs treatment (either whole brain irradiation or stereotactic radiosurgery), and investigating the safety profile of radiation therapy combined with TT or ICI is of high interest. Discontinuing an efficient systemic therapy, when BMs irradiation is considered, might allow systemic disease progression and, on the other hand, the mechanisms of action of these two therapeutic modalities might lead to unexpected toxicities and/or greater efficacy, when combined.

Patients and methods

We carried out a systematic literature review focusing on the safety profile and the efficacy of BMs radiation therapy combined with targeted agents or ICI, emphasizing on the role (if any) of the sequence of combination scheme (drug given before, during, and/or after radiation therapy).

Results

Whereas no relevant toxicity has been noticed with most of these drugs, the concomitant use of some other drugs with brain irradiation requires caution.

Conclusion

Most of available studies appear to advocate for TT or ICI combination with radiation therapy, without altering the clinical safety profiles, allowing the maintenance of systemic treatments when stereotactic radiation therapy is considered. Cognitive functions, health-related quality of life and radiation necrosis risk remain to be assessed. The results of prospective studies are awaited in order to complete and validate the above discussed retrospective data.

Combination of Radiotherapy and Targeted Agents in Brain Metastasis: An Update

OPINION STATEMENT

The combination of radiation therapy and targeted agents (molecular inhibitors or immunotherapy) represents an opportunity to improve the outcomes of patients with brain metastases. The combination of whole-brain radiation therapy (WBRT) with targeted agents takes advantage of radiosensitization, while the combination with stereotactic radiosurgery (SRS) may allow one to substitute an effective systemic agent for adjuvant WBRT, the historical standard of care. This strategy may in turn allow the promotion of secondary prevention paradigms with possibly less cognitive toxicity. At present, the combination of targeted therapy with SRS rather than with WBRT is the more viable option although both avenues will likely have a role in the future management of brain metastases. Patients should be encouraged to enter clinical trials since the off-study use of these combinations will delay the advancement of the field. Caution is advised in the combination of radiation and targeted agents as unexpected toxicities can occur. Clinicians should avail themselves of clinical trials in order to offer patients these promising options and to move the field forward. In the absence of a clinical trial, we recommend the combination of SRS with targeted agents and deferred WBRT. Small, asymptomatic brain metastases may be best managed with single-modality targeted agents with deferred radiation therapy, preferably on a clinical trial. Advances in targeted therapies combined with radiation therapy will most likely improve local control and hopefully the quality of life and survival of patients with brain metastasis.