**12. Complete radiologic response**

Complete radiologic response can be obtained in 5–38% of patients. The frequency of complete radiologic response depends on the efficacy of preoperative treatment and on the quality and completeness of radiologic investigation. Metastasis can become difficult to observe on CT if the size decreases and/or the surrounding liver tissue develops steatosis. MRI can be used to identify the residual lesions. The MRI-documented disappearance of the metastasis is sugges‐ tive of true complete histologic response.

The correlation between radiologic and pathologic complete response ranges 20–100% in different studies. Thus, at present, all sites of disease should be resected surgically. A fraction of lesions (up to 24% of patients with complete response on CT) can be grossly identified during the operation. Full mobilisation of liver and palpation, followed by intraoperative conven‐ tional and contrast-enhanced US, are the subsequent options rising the yield to 45% of patients. Contrast-enhanced US identifies additional 10–15% of nodules, compared with palpation and conventional ultrasonography technique. The intraoperative yield is lower in patients who have had preoperative MRI, suggesting that MRI is the method of choice to identify true small residual metastases that are missed by less sensitive CT [17].

If the radiologically regressed metastases are not resected, they tend to recur. The frequency of durable clinical response, usually defined as disease-free period for 1 year, correlates with the frequency of complete pathologic response. The recurrence mostly develops in 10–20 months. The median time to recurrence is 11 months. The recurrence occurs more frequently in patients who have unresected radiologically disappeared metastases in comparison to those who underwent the surgery, although a more effective adjuvant treatment can diminish these differences. Hepatic arterial infusion treatment lowers the incidence of intrahepatic recurrence and increases the frequency of durable response similarly as increasing the rate of complete pathologic response [17].
