Assessment of metabolic response to pre-operative treatment of rectal cancer

In the era of targeted therapy and high precision radiotherapy for patients with cancer, tailoring and individualization of treatment is needed more and more. In part to avoid ineffective administration of a toxic treatment to a patient that unlikely to get any benefit of it. And also to decrease the expenses of treatment and saving the drugs and resources to patients that deserve. Many predictive factors and markers are searched and well-known in many malignancies, but still rectal cancer lacks such predictors. As the pre-operative chemoradiotherapy is becoming the standard of care of treating patients with locally advanced rectal carcinoma, a predictive factor, or at least an early indicator, of patient's response to treatment is needed. First, it may help to modulate the pre-operative treatment by employing another chemotherapeutic or targeted agent e.g. oxaloplatin or cetuximab instead of the standard fluorouracil compounds. It may also help to avoid continuation of unnecessary protracted course of radiotherapy for 5-6 weeks for a patient who is unlikely to achieve a satisfactory response. This will help to avoid the definite toxicity of pelvic irradiation and avoid wasting time before going to surgery. Here comes the role of imaging techniques in predicting the metabolic response such as functional computerized tomography (CT) and magnetic resonance imaging (MRI) or positron-emission tomography (PET) scan. In this review we will go through the principles, indications and benefits of employing such techniques in the assessment of response to pre-operative chemoradiotherapy of rectal cancer.