Could Local Consolidative Therapy Strategies Bring Survival Benefit for Oligometastatic Carcinoma Patients ― a Systematic Review of Literature From Five Randomized Clinical Trials

Abstract

<h3>Purpose/Objective(s)</h3> The oligometastatic state is an intermediate subset between localized cancer and widely metastatic disease for metastatic cancer patients. Five randomized clinical trials in multiple primary disease sites with limited metastases are performed. It remains controversial whether active local treatment is the optimal strategy for oligometastatic cancer patients. <h3>Materials/Methods</h3> Currently completed randomized clinical trials were reviewed in the clinicaltrials.gov database and extensive searches of the PubMed, Science Direct, Embase, and Cochrane library databases and the terminated date for data retrieval was 31 December 2020. The key terms such as local therapy, SABR ("stereotactic," "stereotaxis") and metastases ("limited, oligo-, metastatic, metastasis, metastasize") were included to capture relevant trials. Data such as one-, two- and three-year progress-free survival (PFS) and overall survival (OS) were collected for meta-analysis to evaluate the efficacy of local therapy. <h3>Results</h3> Five randomized clinical trials including 344 patients met the eligibility criteria. The most common primary disease site was lung, followed by prostate, colorectal, breast and others. The local treatment group had an advantage over the control group in regard to one-year PFS (HR 2.554, 95% CI 1.596-4.088; <i>P</i> < 0.001), two-year PFS (HR 2.104, 95% CI 1.209-3.664; <i>P</i> = 0.009) and three-year PFS (HR 2.839, 95% CI 1.349-5.974; <i>P</i> = 0.006). The local treatment group had an advantage over the control group in three-year OS (HR 2.786, 95% CI 1.664-4.665; <i>P</i> < 0.001); nevertheless, the two groups showed similar results in one year OS (HR 1.306, 95% CI 0.746-2.284; <i>P</i> = 0. 35) and two-year OS (HR 1.543, 95% CI 0.961-2.476; <i>P</i> = 0. 072). <h3>Conclusion</h3> The concept of oligometastasis is essentially due to the development of therapies for tumor, such as targeted therapy and immunotherapy, and the prolongation of survival time of patients, which makes the role of local treatment more and more attention. Based on the available evidence, the addition of local consolidative therapy to oligometastatic carcinoma patients provided an advantage on PFS and long-term survival. As an exception, the PFS of one-, two-, three-year and three-year OS could be improved with the local therapy for oligometastatic carcinoma patients. While surgery, stereotactic radiotherapy and chemotherapy are the cornerstones of current treatment strategies, future clinical trials need to address the high risk of distant metastases by integrating targeted therapy or immunotherapy.