Abscopal effect in lung cancer: three case reports and a concise review

The abscopal effect describes the ability of locally administered radiotherapy to induce systemic antitumor effects. The mechanism responsible for this effect is immune mediated: irradiated tumor cells stimulate antitumor adaptive immunity by inducing the release of tumor antigens and their cross-presentation to CD8⁺ T-cells.

We present three case reports of the abscopal effect in patients with metastatic lung cancer treated with radiotherapy and immunotherapy observed at the Lungenfachklinik Immenhausen.

The first patient presented an abscopal remission of adrenal metastases following thoracic radiotherapy and nivolumab. The second one showed an abscopal response to lung cancer and mediastinal lymph nodes after whole brain radiotherapy and atezolizumab. The third patient, treated with pembrolizumab, presented an abscopal regression of thoracic (lung and pleural) disease following whole brain radiotherapy.

Over the past 40 years, reports on the abscopal effect following conventional radiation have been relatively rare, in particular in less immunogenic tumors such as lung cancer. However, with the continued development and use of immunotherapy, reports on the abscopal effect have become increasingly frequent during the last decade. Performing a systematic literature search for case reports of the abscopal effect following radiotherapy in patients with non-small cell lung cancer, we identified 11 cases. Reports about the abscopal effect in lung cancer have appeared regularly since 2013, next to a potential awareness among clinicians that introduction of immunotherapy seems to play a role in this phenomenon.

With the development of immune checkpoints inhibitors, the abscopal effect of radiotherapy might become more frequent. Immunotherapy can potentiate the in situ vaccination effect of radiotherapy.

Many challenges remain for this combined treatment as the optimal dose/fractionation schemes for radiotherapy, the optimal time of administration of immunotherapy and the prediction of treatment efficacy are still unclear. These questions need to be addressed in future clinical studies with the aim of developing evidence-based guidelines for radiotherapy and immunotherapy.