Imaging beyond RECIST: CT and MRI in molecular therapies

Abstract

Until recently, almost all systemic antineoplastic therapies in cancer patients aimed at destruction of tumor cells, i.e. they were cytotoxic. The effect of therapy was assessed by measuring the tumor size with a decrease in size suggesting response to therapy and an increase suggesting progression. Modern molecular therapies, however, are mostly not cytotoxic but aim to reduce tumor perfusion or metabolism by blocking specific cell functions without causing cell death. Assessment of tumor size alone may, therefore, not be appropriate in this setting and can even lead to false conclusions. This presentation gives examples of changes at computed tomography (CT) and magnetic resonance imaging (MRI) of tumors undergoing therapy with molecular therapies, highlights potential pitfalls und suggests criteria for response assessment. The presentation focuses on CT and MRI of chest and abdominal tumors and specifically excludes positron emission tomography/CT and brain tumors.

Figure 1

An 81-year-old man with colorectal cancer and liver metastases before (a) and after (b) initiation of therapy with bevacizumab (Avastin™). A lesion in segment 7 is identified before and after initiation of therapy, a lesion in segment 4A, however, is seen only after initiation of therapy.

Figure 2

A 74-year-old woman with GIST and liver metastases before (a), 2 months (b) and 5 months (c) after initiation of therapy with imatinib (Gleevec™).

Figure 3

A 61-year-old man with GIST and liver metastases. All metastases appear hypodense at contrast-enhanced CT (a). One metastasis is hyperintense at T1-weighted MRI (b) due to spontaneous hemorrhage into the metastasis.

Figure 4

A 55-year-old man with GIST and liver metastases on imatinib therapy. Purely hypodense lesion at baseline (a), new soft tissue density lesion (nodule) within the cyst after 9 months (b) with further growth after 18 months (c) and 27 months (d) representing progression.