Colorectal cancer (CRC), the fourth most common malignancy worldwide, remains by far the first cause of liver metastases and the first liver malignancy in Western societies.1 It is estimated that about half of these patients will develop colorectal liver metastases (CLM) during the course of disease (metachronous liver metastases), whereas 15% to 25% of the patients already present CLM at the time of the diagnosis (synchronous liver metastases).2,3
Colorectal liver metastases have become a specific oncological entity since CLM are commonly confined to the liver, by contrast to other malignancies in which liver involvement is usually part of disseminated disease. Moreover, CLM is no more considered as a terminal stage since, in some patients, resection has a potential for cure.4
Synchronous Colorectal Liver Metastases
Synchronous metastases are more frequently observed in younger patients. French regional registry reported that 19.8% of patients younger than 55 years had concomitant CLM at diagnosis versus 11.7% of those over 75 years.2 Similar trends were noted in other large population-based studies.5,6 It is estimated that extrahepatic metastatic disease is present in about 25% of patients with synchronous CLM.
Metachronous Colorectal Liver Metastases
There is no consensus on the definition of metachronicity. The term “metachronous” defined CLM that become detectable on imaging after an interval time period ranging from 3 months to 1 year after the diagnosis of the primary tumor.7 Although the majority of metachronous CLM are diagnosed within the 2 years following colorectal resection, they can appear beyond 5 years of the primary tumor resection.8 The risk of developing CLM decreases with time. The main risk factor for developing metachronous CLM is lymph node involvement of the primary tumor (stage III CRC). Other pathological features found on the specimen, such as vascular invasion, perineural invasion, and immune response, are also independent factors of relapse after resection of the primary.
Noteworthy, it is now admitted that an important proportion of patients with so-called metachronous CLM in the past should have been rather considered as synchronous. Indeed, dramatic improvement of imaging over the last decades makes now possible to diagnose small lesions, previously undetectable. This misclassification has originated an underestimation of the proportion of patients with synchronous CLM.
In most cases, the diagnosis of CLM is performed in the setting of two different situations:
During the follow-up of resection of a primary colorectal tumor
At the discovery of multiple hepatic lesions in patients with no history of primary cancer
In the first situation, the diagnosis is based on clinical history and imaging studies. In the other presentation modality, as the origin of the primary governs the therapeutic project, it is recommended to identify the primary tumor by a workup ...