How effective is external beam radiotherapy for treating colon cancer?

Fairly effective: Best used in the neoadjuvant setting to reduce the size of a rectosigmoid lesion to improve operability. In terms of long term survival this has not been achieved without the addition or RT. Better results can be anticipated when RT is combined with immunochemotherapy. It is also used palliatively if a large metastatic disease is present in the pelvis and the primary has already been resected.