Imaging in disappearing colorectal liver metastases and their accuracy: a systematic review.

BACKGROUND: Approximately 30% of patients with colorectal cancer develop colorectal liver metastases (CRLM). CRLM that become undetectable by imaging after chemotherapy are called disappearing liver metastases (DLM). But a DLM is not necessarily equal to cure. An increasing incidence of patients with DLM provides surgeons with a difficult dilemma: to resect or to not resect the original sites of DLM? The aim of this review was to investigate to what extent a DLM equates a complete response (CR) and to compare outcomes. METHODS: This review was conducted in accordance with the PRISMA guidelines and registered in Prospero (registration number CRD42017070441). Literature search was made in the PubMed and Embase databases. During the process of writing, PubMed was repeatedly searched and reference lists of included studies were screened for additional studies of interest for this review. Results were independently screened by two authors with the Covidence platform. Studies eligible for inclusion were those reporting outcomes of DLM in adult patients undergoing surgery following chemotherapy. RESULTS: Fifteen studies were included with a total of 2955 patients with CRLM. They had 4742 CRLM altogether. Post-chemotherapy, patients presented with 1561 DLM. Patients with one or more DLM ranged from 7 to 48% (median 19%). Median DLM per patient was 3.4 (range 0.4-5.6). Patients were predominantly evaluated by contrast-enhanced computed tomography (CE-CT) before and after chemotherapy, with some exceptions and with addition of magnetic resonance imaging (MRI) in some studies. Intraoperative ultrasound (IOUS) was universally performed in all but two studies. If a DLM remained undetectable by IOUS, this DLM represented a CR in 24-96% (median 77.5%). Further, if a DLM on preoperative CE-CT remained undetectable by additional workup with MRI and CE-IOUS, this DLM was equal to a CR in 75-94% (median 89%). Patients with resected DLM had a longer disease-free survival compared to patients with DLM left in situ but statistically significant differences in overall survival could not be found. CONCLUSION: Combination of CE-CT, MRI, and IOUS showed promising results in accurately identifying DLM with CR. This suggests that leaving DLM in situ could be an alternative to surgical resection when a DLM remains undetectable by MRI and IOUS.