Management of disappearing colorectal liver metastases.

The development of new potent systemic treatment modalities has led to a significant increase in survival of patients with colorectal liver metastases. In the neo-adjuvant setting, these modalities can be used for patient selection, down staging, and conversion from non-resectable to resectable liver metastases. In addition, complete radiological disappearance of metastases can occur, the phenomenon of disappearing liver metastases. Because only a small percentage of these patients (0-8%) have a complete radiological response of all liver metastases, most patients will undergo surgery. At laparotomy, local residual disease at the site of the disappeared metastasis is still found in 11-67%, which highlights the influence of the imaging modalities used at (re)staging. When the region of the disappeared liver metastasis was resected, microscopically residual disease was found in up to 80% of the specimens. Alternatively, conservative management of radiologically disappeared liver metastases resulted in 19-74% local recurrence, mostly within two years. Obviously, these studies are highly dependent on the quality of the imaging modalities utilised. Most studies employed CT as the modality of choice, while MRI and PET was only used in selective series. Overall, the phenomenon of disappearing liver metastases seems to be a radiological rather than an actual biological occurrence, because the rates of macroscopic and microscopic residual disease are high as well as the local recurrence rates. Therefore, the disappeared metastases still require an aggressive surgical approach and standard (re)staging imaging modalities should include at least CT and MRI.