Parenchymal sparing surgery brings treatment of colorectal liver metastases into the precision medicine era.

The treatment of advanced colorectal liver metastases (CRLMs) follows the biphasic pattern characteristic of oncological surgery. A phase of escalation-the therapeutic aggressiveness-is followed by a phase of de-escalation aimed at decreasing the morbidity, while preserving the gains in survival. From a maximum of three lesions, the rule no longer limits the number, provided the intervention does not cause lethal liver failure. Technically feasible non-anatomical resections, two-stage hepatectomies, portal vein obliteration and so forth, have pushed the boundaries of surgery far. However, the impact and the biology of metastatic processes have been long ignored. Parenchymal sparing surgery (PSS) is a de-escalation strategy that targets only metastasis by minimising the risk of stimulating tumour growth, while enabling iterative interventions. Reducing the loss of healthy parenchyma increases the tolerance of the liver to interval chemotherapy. Technically, PSS could use any type of hepatectomy, providing it is centred on the metastatic load alongside intraoperative ablation. The PSS concept sometimes wrongly comes across as a debate between minor versus major hepatectomies. Hence, we propose a clear definition, both quantitative and qualitative, of what PSS is and what it is not. Conversely, the degree of selectivity of PSS as a percentage of the volume of resected metastases versus the volume of total liver removed has not been stopped to date and should be the subject of prospective studies. Ultimately, the treatment of advanced CRLMs, of which PSS is a part, needs to be personalised by the multidisciplinary team by adapting its response to each new recurrence.