Tumor pseudoresponse, also known just as pseudoresponse, refers to the phenomenon of tumors appearing to respond to a specific treatment on imaging criteria, when the lesion actually remains stable or has even progressed.
The term is largely used in brain tumors imaging follow-up, especially for high grade gliomas (e.g. glioblastoma) in which a rapid decrease in contrast enhancement and edema can be observed in a short period of time after administration of antiangiogenic agents (e.g, bevacizumab and cediranib), often without any significative change in actual tumor size (as visualized by T2 (non-enhancing tumor) or diffusion / perfusion studies 1-3.
Bevacizumab (trade name Avastin) for example, is an inhibitor of vascular endothelial growth factor (VEGF), aimed at inhibiting the formation of new blood vessels within the tumor (neoangiogenesis). VEGF is produced by the tumors, and not only promotes neoangiogenesis but also reduces effectiveness of gap junctions and creates fenestrations in the endothelium of existing brain capillaries, leading to edema and enhancement 4. The amount of VEGF produced has been shown to correlate with tumor grade.
The changes seen in pseudoresponse (rapid reduction in enhancement and vasogenic edema) are largely mediated by changes in blood brain barrier permeability rather than antiangiogenic effects, meaning that relying on enhancement and T2 signal change can be misleading when interpreting follow up MRI studies 4.
MR spectroscopy, MR perfusion (particularly cerebral blood volume) and diffusion weighted imaging (DWI) are particularly important in assessing for the presence of residual, but now non-enhancing, tumor.
Despite the fact that these advanced MRI sequences have helped in differentiating pseudoresponse from a true response, imaging follow-up is still required 1. Essential to correct interpretation is the availability of multiple previous imaging studies and information relating to type and timing of therapy.
- 1. Hygino da Cruz LC, Rodriguez I, Domingues RC et-al. Pseudoprogression and pseudoresponse: imaging challenges in the assessment of posttreatment glioma. AJNR Am J Neuroradiol. 2011;32 (11): 1978-85. doi:10.3174/ajnr.A2397 - Pubmed citation
- 2. Brandsma D, van den Bent MJ. Pseudoprogression and pseudoresponse in the treatment of gliomas. Curr. Opin. Neurol. 2009;22 (6): 633-8. doi:10.1097/WCO.0b013e328332363e - Pubmed citation
- 3. Clarke JL, Chang S. Pseudoprogression and pseudoresponse: challenges in brain tumor imaging. Curr Neurol Neurosci Rep. 2009;9 (3): 241-6. Pubmed citation
- 4. Blake MA, Kalra MK. Imaging in Oncology. Springer Science & Business Media. (2008) ISBN:038775587X. Read it at Google Books - Find it at Amazon
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