Development of a Genome-based Platform for Personalized Treatment in Locally Advanced Rectal Cancer Patients

This study is aimed to develop a genome-based platform to predict patients who can achieve pathologic complete response after neoadjuvant treatment in locally advanced rectal cancer. The main treatments for locally advanced rectal cancer is surgical removal such as lower anterior resection after neoadjuvant CCRT. About 10-40% of patients showed pathologic complete response after neoadjuvant CCRT. Mandard tumor regression grade (TRG) is used to grade the histologic tumor response after neoadjuvant treatment. TRG 1 represents the pathologic complete response and TRG2 as histologically small group of cancer cells. Accordingly, TRG1 and 2 are expressed as good responder. Even though the surgery is being performed as an essential treatment, there are various surgery-related sequelae such as colostomy. Also, in some patients, surgery may be refused or surgery may not be performed due to an underlying disease. About 15-20% of local recurrence was reported in patients who did not undergo surgery and the 3-year survival rate was 96.6%. Colorectal cancer genetically can be divided into 4-subtypes. With the recent development of genome testing technology, genome analysis has been actively conducted in colorectal cancer. The most commonly known genetic subtype of colorectal cancer is classified into a total of 4 types as consensus molecular subtype (CMS); CMS1, CMS2, CMS3, CMS4. However, this was analyzed in colorectal cancer patients who did not undergo radiotherapy. There is no data regarding the response to radiation therapy according to each genetic subtype. Therefore, classifying the subtypes through genomic analysis and studying the responsiveness to radiotherapy in each subtype is needed. In this study, we aimed to develop a platform that predicts pathologic tumor response after CCRT based on genomic information. Furthermore, being able to select patients who can wait-and-see without surgery using platform.

The treatment in this study is one of the standard treatments suggested by the NCCN guidelines. The patients received operation after neoadjuvant concurrent chemoradiotherapy and pathologic tumor response is evaluated. Before neoadjuvant treatment, the following are obtained; Medical history and physical examination, Tissue acquisition through colonoscopy, Blood Test (CBC), Chemistry Test (SMA), staging through pelvic CT or MRI, PET-CT or chest CT. Either 5-FU/leucovorin and Capecitabine based concurrent chemoradiotherapy is conducted. The target delineation is performed in 3mm simulation CT for radiotherapy. GTV includes primary lesions ,lymph nodes and mesorectum based on diagnostic CT, MRI, and PET-CT. CTV covers the perirectal and internal pelvic lymph node with microscopic margin of GTV. PTV1 is defined as extending 0.3cm from the GTV. PTV2 is defined as extending 0.5 from CTV. Radiotherapy is performed using 3D conformal radiotherapy, intensity-modulated radiotherapy, volumetric modulated Arc therapy. Radiotherapy is administered daily, five times a week according to the NCCN guidelines. Each treatment is performed with full bladder and prone positioning. Radiotherapy is performed 25 fractions with simultaneous integrated boost method. 2.00Gy is administered for PTV1 while 1.8 Gy is administered for PTV2. The operation is performed 5-12 weeks after CCRT. If the patients refuse, physicians do not perform surgery and undergo wait-and-see. The treatment response is evaluated based on standard treatment process. During the treatment, the regular check up is conducted to evaluate the acute toxicity regarding treatment. The acquired specimens are used for RNA sequencing and organoid construction. The RNA sequencing is used to analyze the differentially expressed based on treatment response to neoadjuvant concurrent chemoradiotherapy.