EXtended CriteriA Treatment for LIver Metastases With Heavy Tumour BURden 1 + 2

1.1 Background - Disease Colorectal cancer (CRC) is the second most frequent malignant disease in Norway (Cancer in Norway 2017). About 50% of the patients will have metastatic disease at time of diagnosis or develop metastatic disease later on. Liver metastases are the most frequent site of metastatic disease. Liver resection is considered the only curative treatment option in CRC patients with liver metastases, however only about 20% of the patients are candidates for liver resection. The treatment option for the majority of the patients is palliative chemotherapy with median overall survival from start of chemotherapy of about 2 years and 10-12 months from starting second line chemotherapy.

1.2 Liver resections for Colorectal Liver metastases (CRLM) While high-quality data (randomized trials) are lacking, it is generally accepted that the only curative treatment for colorectal liver metastases (CRLM) is surgery. Liver resections are generally well tolerated and safe 1, but some patients recur early and probably have limited or no benefit from surgery. These are hard to identify upfront. Even following three decades of systematic liver surgery for CRLM, there is a lack of robust prognostic scoring systems that have sufficient discriminatory power to serve as selectors for surgery or non-operative treatment 2, 3. Even among patients with very poor prognostic scores, there are some who will survive five years following surgery 4, and even without surgery 5. Over the decades, the definition of resectability/un-resectability has been steadily modified. Today, any configuration of metastases can be deemed resectable as long as a resection will leave behind a working liver volume of at least 20-30 % of the estimated total liver volume with a functioning arterial inflow, portal venous inflow, draining bile duct and draining hepatic vein.

1.3 The grey zone As resections are generally well tolerated and adequate prognostication is wanting, there is a tendency to offer resections to patients who have borderline resectable CRLM or who exhibit other non-favourable traits like large or multiple metastases. For patients who have early recurrence of disease, such resections represent a net loss of quality-of-life and an unwanted expenditure for society. Exploring the optimal treatment modality for patients in this grey zone, i.e. with uncertain benefit from surgery, is important to avoid unnecessary resections and providing the optimal treatment for patients in a critical situation.

1.4 Systemic chemotherapy for CRLM Palliative chemotherapy is in general the only treatment option for the vast majority of non-resectable patients. The expected median overall survival (OS) from start of first line chemotherapy is about 2 years and the 5 years OS is about 10%, although, longer median OS has been obtained in selected patients with good performance status (ECOG 0-1), no (K)RAS or BRAF mutations and left-sided tumors 6-10. OS from start of second line chemotherapy is 10-12 months 11.

1.5 Liver transplant for CRLM Liver transplant (LTX) has emerged as a possible solution for some patients with unresectable CRLM who otherwise have good prognosis based on available scorings systems 12, 13. In patients with non-resectable liver only metastases the investigators have previously shown 5 year OS of 56% compared to 9% in a similar cohort of patients starting first line chemotherapy 6, but due to lack of donor organs this will never become the backbone of any treatment modality for a disease as prevalent as CRLM. However, LTX is probably the best treatment option in highly selected patients with non-resectable CRLM liver only disease.