Impact of Right-sided Primary Tumor Location Among Patients With Oligometastatic Colorectal Cancer Treated With Stereotactic Body Radiotherapy

Introduction: Among patients with colorectal cancer, those with right-sided primary tumors have worse outcomes in both the primary and metastatic setting. Patients with oligometastatic colorectal cancer (OMCC) have improved prognosis relative to those with diffusely metastatic disease. We aimed to assess if the trend toward worse outcomes with right-sided tumors remained in the oligometastatic setting. Patients and Methods: We analyzed 31 patients treated at a single institution with stereotactic body radiotherapy for OMCC from 2011 to 2014 to assess the impact that primary tumor location had on overall survival (OS) and progression-free survival (PFS). Results: Overall, patient local control was fair (66% at 2 y); however, distant control was only 37.4% at 2 years. The median OS was 2.4 years; the median PFS was 6.5 months. Patients with right-sided primary tumors had numerically worse median OS than those with left-sided or rectal primary tumors (1.4 vs. 3.7 y, P=0.09). Median PFS was significantly worse among those with right-sided primaries (2.9 vs. 10.8 mo, P=0.05). This held on multivariate analysis. Conclusions: These results affirm that patients with OMCC have extended OS periods and that stereotactic body radiotherapy offers strong local control in these settings. We show that even in the oligometastatic setting those with right-sided primary tumors have worse outcomes relative to those with left-sided or rectal primary tumors. This suggests more aggressive treatment may be needed for those with oligometastatic right-sided colorectal cancer.

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