The purpose of this study is to evaluate the efficacy of Durvalumab plus Regorafenib versus observation for patients with stage IV colorectal cancer achieving the no evidence of disease state.

The NED state can be achieved in any line of treatment and it is defined as:

1. R0 resection for surgery,
2. the complete ablation defect covering the lesion on CT scan for radiofrequency,
3. the erogation of ≥ 60 Gy for stereotactic radiotherapy,
4. complete response to antineoplastic treatments on CT scan. In all these cases CEA and CA 19.9 must be within normal limits at the time of randomization.

Participants in this study will receive:

Experimental arm:

Regorafenib 90 mg d1-21 every 28 days plus Durvalumab 1500 mg every 28 days for 1 year

Control arm:

Observation (crossover to Experimental arm is allowed in case of relapse)

Tumor assessment will be performed every 12 weeks.

The safety run-in phase is planned for the first 4 patients randomized to the experimental arm using a starting dose of 60 mg/die of Regorafenib (and fixed 1500 mg of Durvalumab), to be escalated after 2 months to 90 mg/die if < 2 patients report serious adverse events.

Inclusion Criteria:

1. ≥ 18 years; ECOG PS 0-1;
2. Body weight >30 kg;
3. Histologically confirmed diagnosis of colorectal adenocarcinoma;
4. Patients must be in NED after completion of any treatments for stage IV CRC, including resections, RFA; RT with or without neoadjuvant/adjuvant therapies or CR after chemotherapy;
5. Patients must be randomized within 10 weeks since the achievement of the NED state. Those who have also received adjuvant therapy following the locoregional treatment are still eligible, provided they are randomized within 4 weeks since the last chemotherapy cycle;
6. NED state ascertained by means of CT scan and/or PET scan and/or MRI scan;
7. Life expectancy of at least 12 weeks;
8. CEA within normal limits;
9. No residual toxicity from previous chemotherapy;
10. Adequate organ function;

Exclusion criteria:

1. MSI/dMMR patients;
2. Any unresolved toxicity NCI CTCAE Grade ≥2 from previous anticancer therapy with the exception of alopecia and vitiligo;
3. Active or prior documented autoimmune or inflammatory disorders;
4. Relevant concomitant comorbidities;