Implementing Non-invasive Circulating Tumor DNA Analysis to Optimize the Operative and Postoperative Treatment for Patients With Colorectal Cancer

1. INTRODUCTION Colorectal cancer (CRC) is the third most common cancer worldwide. Approximately two-thirds of patients initially present with potentially curable disease but in spite of curatively intended treatment 30-40% experience relapse of disease. When diagnosed, survival of CRC can basically be improved in two ways, 1) by reducing the risk of recurrence all together, e.g. by improving surgery or by offering adjuvant chemotherapy to the patients with high risk of recurrence, or 2) by early detection of recurrence enabling early intervention which improve patient survival significantly.

Radical surgery is the most important factor for recurrence and survival of CRC, and free margins of resection are of paramount importance. Initiatives to optimize the quality of surgery, including resection within the correct planes and adherence to the concept of complete mesocolic excision with central ligation of the tumor feeding arteries, are currently being implemented in Denmark. A single Danish center (Hillerød Hospital) which have implemented this technique have reported substantial higher survival rates compared to similar Danish centers using standard surgery.

Randomized trials have shown that the therapeutic benefit of adjuvant chemotherapy is modest, while the toxicity is substantial. Accordingly, treatment benefit has only been documented for the patients with the highest risk of recurrence (stage III). Nevertheless, also a subset of stage I and stage II patients recur and could potentially benefit from adjuvant therapy. Development of a sensitive approach for assessing if occult residual disease is present after surgery is highly desirable to identify a high-risk sub-group who should be offered adjuvant therapy. Moreover, for stage III disease it is well documented that many patients are overtreated with adjuvant therapy. Surgery alone cures > 40% of such patients and the number needed to treat to prevent a relapse is ~7. Also for these patients, there is need for better and more specific markers of risk of recurrence.

Solid tumors, including CRC, release DNA fragments into plasma. The plasma of cancer patients contains DNA fragments from both normal and cancer cells. This DNA is referred to as cell free DNA (cfDNA), while the specific fraction that originates from tumor cells is called circulating tumor DNA (ctDNA). The investigators have recently presented results that, in line with others, indicate that patients with ctDNA detected post-surgery are at extremely high risk of a later radiologic recurrence (HR=37.66; 95% CI, 4.23 to 335.49; P<0.0001). This risk is greater than that in patients with stage III colorectal cancer who are routinely treated with adjuvant therapy. These findings show that post-operative ctDNA analysis has potential to become a highly valuable tool for assessment of the quality of the primary surgery and for guiding the use of adjuvant therapy.

In agreement with others, the investigators have shown that ctDNA changes detected through longitudinal analysis correlates closely with changes in tumor volume as assessed by CT-imaging. Thus, ctDNA analysis has potential as a tool for assessing the impact of intervention (e.g. chemotherapy, surgery, radio frequency ablation (RFA), and stereotactic body therapy (SRBT)). The investigators have shown that serial ctDNA analysis enable detection of incipient clinical disease recurrence on average 10 months before by the conventional modalities (primarily CT-scan. Accordingly, ctDNA analysis has the potential to provide a critical window of opportunity for intervention at an early time-point where curative modalities are still an option. 2. INVESTIGATIONAL PLAN 2.1 Overall study design The IMPROVE - OBSERVATIONAL STUDIES are based on a comprehensive series of blood sampling and ctDNA analysis performed in CRC patients before and after surgery, during and after adjuvant chemotherapy, and during surveillance. Patients are followed 5 years from date of surgery.