Objective: The liver is one of the most common sites of metastatic disease. The increasing use of molecular targeted therapy, including antiangiogenic agents, mammalian target of rapamycin inhibitors, and various monoclonal antibodies, for the treatment of various carcinomas and sarcomas has rendered use of simple size measurements for the assessment of treatment response inadequate. Several atypical patterns of treatment response, at times mimicking tumor progression, are increasingly seen, leading to confusion. The purpose of this article is to familiarize the reader with the unusual patterns in which liver metastases respond to molecular targeted therapy and help differentiate treatment response mimicking progression (pseudo-progression) from true progression.
Conclusion: In the era of molecular targeted therapy, every radiologist who interprets oncologic studies needs to be aware of the unusual patterns of treatment response and should be able to differentiate pseudoprogression of liver metastases from true progression because this distinction has an important impact on clinical management.