Stereotactic Ablative Body Radiotherapy (SABR) for Oligometastases

Metastatic Tumors

Cancer

This is a study measuring toxicity while making observations about the survival benefits of treating participants with oligometastatic disease using stereotactic ablative radiotherapy (SABR).

To assess quality of life and side effects in participants with up to 5 metastatic cancer lesions treated with a comprehensive oligometastatic SABR treatment program. Secondarily, the investigators will document the disease free and overall survival. Rationale: The oligometastatic state was first defined in 1995 and refers to a stage of disease where cancer has spread beyond the site of origin, but is not yet widely metastatic. In such a state of limited metastatic disease, it is hypothesized that eradication of all sites of metastatic disease could result in long-term survival, or even cure, in some participants. Ablation of metastatic deposits can be achieved through several techniques, including surgery, radiofrequency ablation (RFA), or through Stereotactic ablative body radiotherapy (SABR), a new radiotherapy technology that delivers very large, hypofractionated doses of radiotherapy to small tumor targets, with high rates of local control. Clinical evidence to support the presence of an oligometastatic state is controversial. However, there is emerging low quality evidence in both the surgical and SABR literature that this state may exist. In a study of over 5200 participants with lung metastases who underwent surgical resection, a 5-year survival of 36% was reported in participants who achieved a complete resection, much higher than would be expected for stage IV disease.3 Similarly, in participants treated with SABR for 1-3 lung metastases from a variety of primary tumors, local control with SABR was 96% at 2-years, and 2-year survival was 39%. Long-term survival has been demonstrated in participants treated for oligometastases with surgery or SABR at several other tumor sites, including liver, brain, bone, and adrenal metastases. The risk of further metastases after ablative treatment is up to 60-80% in some studies. SABR can also be used for further salvage at newly progressive sites (oligoprogression). Despite the apparent achievement of long-term survival with ablative treatment for oligometastatic disease, the level of evidence to support such treatments is weak, often based on single-arm studies without appropriate controls. Participants included in such reports are highly selected, based on good performance status and slow pace of tumor progression. It has been suggested that the long-term survival achieved with treatment of oligometastases is a result of the selection of fit participants with very slow-growing tumors, rather than the result of treatment intervention. Randomized trials are therefore necessary to establish the utility of ablative treatment of oligometastatic disease, and therefore the BCCA oligometastatic SABR group, recommends that participants be considered for a randomized control before being offered SABR on this current trial. In some circumstances, participants may not be comfortable with this approach, or their physicians do not have clinical equipoise, and therefore SABR for oligometastatic disease may be appropriate. BCCA has decided that given the limited evidence for SABR in this setting, it will not be offered off trial. The main focus of this trial is to assess the side effects and quality of life post SABR. This trial aims to provide a clear informed consent process, including the limited evidence for SABR off trial, and potential harm from SABR, for participants opting to pursue SABR for oligometastases. This is a non-randomized phase II trial where all participants will receive experimental SABR to all sites of metastatic disease. The investigators will accrue 200 participants to assess toxicity associated with this experimental treatment.

Canada