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Radiation therapy (RT) can induce an immunogenic variant of regulated cell death that can initiate clinically relevant tumor-targeting immune responses. Immunogenic cell death (ICD) is accompanied by the exposure and release of damage-associated molecular patterns (DAMPs), chemokine release, and stimulation of type I interferon (IFN-I) responses. In recent years, intensive research has unraveled major mechanistic aspects of RT-induced ICD and has resulted in the identification of immunogenic factors that are released by irradiated tumor cells. However, so far, only a limited number of studies have searched for potential biomarkers that can be used to predict if irradiated tumor cells undergo ICD that can elicit an effective immunogenic anti-tumor response. In this article, we summarize the available literature on potential biomarkers of RT-induced ICD that have been evaluated in cancer patients. Additionally, we discuss the clinical relevance of these findings and important aspects that should be considered in future studies.

Background. Median survival after diagnosis of brain metastases is, depending on the Recursive Partitioning Analysis (RPA) classes, 7.1 (class I) to 2.3 months (class III). In 2011 the Dutch guideline on brain metastases was revised, advising to withhold whole brain radiotherapy (WBRT) in RPA class III. In this large retrospective study, we evaluated the guideline's use in daily practice. Material and methods. Data of 428 lung cancer patients undergoing WBRT for brain metastases (2004-2012) referred from three Dutch hospitals were retrospectively analyzed. Details on Karnofsky performance score (KPS), age, control of primary tumor, extracranial metastases, histology, and survival after diagnosis of brain metastases were collected. RPA class was determined using the first four items. Results. In total 327 patients had non-small cell lung cancer (NSCLC) and 101 small cell lung cancer (SCLC). For NSCLC, 6.1%, 71.9%, and 16.2% were classified as RPA I, II, and III, respectively, and 5.8% could not be classified. For SCLC this was 8.9%, 66.3%, 14.9%, and 9.9%, respectively. Before the revised guideline was implemented, 11.3-21.3% of WBRT patients were annually classified as RPA III. In the year thereafter, this was 13.0% (p = 0.646). Median survival (95% CI) for NSCLC RPA class I, II, and III was 11.4 (9.9-12.9), 4.0 (3.4-4.7), and 1.7 (1.3-2.0) months, respectively. For SCLC this was 7.9 (4.1-11.7), 4.7 (3.3-6.1), and 1.7 (1.5-1.8) months. Conclusions. Although it is advised to withhold WBRT in RPA class III patients, in daily practice 11.3-21.3% of WBRT-treated patients were classified as RPA III. The new guideline did not result in a decrease. Reasons for referral of RPA III patients despite a low KPS were not found. Despite WBRT, survival of RPA III patients remains poor and this poor outcome should be stressed in practice guidelines. Therefore, better awareness amongst physicians would prevent some patients from being treated unnecessarily. [ABSTRACT FROM AUTHOR]

Simple Summary: The historical standard treatment of metastatic non-small cell lung cancer (NSCLC) consisted of palliative chemotherapy, with limited influence on survival. With the introduction of immuno- and targeted therapy, the prognosis improved largely. A subset of NSCLC patients with limited metastatic disease, called oligometastatic, might obtain long-term survival by adding a local ablative treatment on all visible disease sites, in addition to the standard systemic treatment. The evidence for this combined treatment is still scarce and comes mainly from the pre-immunotherapy era. As radiotherapy might stimulate the immune system making immunotherapy more efficient, here we review the evidence before and in the era of immunotherapy, and discuss the challenges and prospects of the combined treatment. Oligometastatic cancer is recognized as a separate entity within the spectrum of metastatic disease. It was suggested that patients with oligometastatic disease can obtain long-term survival by giving local ablative therapy (LAT) to all visible disease locations. However, the true extent from which metastatic cancer should be called "oligometastatic" is unknown, although a consensus definition for oligometastatic disease is proposed by research organizations, such as the EORTC (maximum of five metastases in three organs). Different states of the oligometastatic disease are defined, such as synchronous vs. metachronous, oligopersistent vs. oligoprogressive disease. All clinical trials including patients with non-small cell lung cancer (NSCLC) are small and most are not randomized. Two small randomized phase II trials on synchronous disease showed an improvement in progression free survival, with the addition of LAT, and one also demonstrated an overall survival benefit. Immune checkpoint inhibitors (ICI) were not part of the treatment in these trials, while ICI significantly improved long-term outcomes of patients with metastatic NSCLC. Radiotherapy might improve the prognosis of patients treated with ICI because of its immunostimulatory effects and the possibility to eradicate metastatic deposits. Here, we summarize the data for adding ablative radiotherapy to the treatment of oligometastatic NSCLC, especially in the ICI era, and discuss the challenges of combined treatment. [ABSTRACT FROM AUTHOR]