What is the outcome after treatment of gastric cancer? There are still some limitations in the evaluation of the efficacy of the common imaging tools, for example, it is difficult to evaluate a cavernous organ such as gastric cancer using the existing RECIST criteria (i.e., solid tumor efficacy evaluation criteria), and on the other hand, imaging changes are “hindsight”, with morphological changes often occurring later than changes in tissue composition.
The rapid development of medical imaging technology has led to new tools for assessing the efficacy of gastric cancer treatment.
Energetic spectral CT
Traditional CT is a “qualitative” imaging that can determine the nature of most gastric cancer lesions. Energy-spectrum CT is a precise “quantitative” imaging technique that allows for a “numerical” assessment of the efficacy of gastric cancer treatment through changes in iodine concentration values, i.e., a quantitative assessment.
The use of energy-spectrum CT allows physicians to detect changes in size and shape before they are observed on imaging, so that they can make timely judgments about the effectiveness of treatment.
Magnetic resonance diffusion-weighted imaging (DWI) technology
Before treatment, the diffusion of water molecules is blocked when the tumor tissue is intact. With partial necrosis of the tumor tissue after treatment, the resistance to diffusion of water molecules is reduced, and therefore the ADC value (short for apparent diffusion coefficient) appears to decrease.
DWI is a technique that detects changes in ADC values of tumor tissue during treatment to detect the changes brought about by treatment, which is a reflection of the effect of treatment. Unlike conventional imaging, where morphological changes are observed after 2 to 3 weeks of treatment, DWI technology allows changes to be observed soon after treatment, usually about 1 hour after treatment.
Based on DWI technology, physicians can make predictions about the efficacy of treatment. Identifying trends in quantitative changes in tumor ADC values early in treatment can provide an early indication of possible drug resistance.
Dynamic enhanced magnetic resonance imaging (DCE-MRI)
DCE-MRI is an imaging technique without radiation damage that can quantify the characteristics of tumor angiogenesis and detect changes in tumor blood supply, changes in blood permeability, and many other changes. This tool is particularly suitable for the assessment of efficacy after targeted anti-angiogenic therapy.
For gastric cancers that are difficult to assess at the primary site, some reduction in metrics can be observed by DCE-MRI after treatment. This tool reflects the numerical changes and can exclude the interference of subjective judgments of the examiner.
Imaging histological assessment
Artificial intelligence is increasingly involved in medical diagnosis, and imaging histology combines artificial intelligence with imaging tools to build imaging databases and data models related to treatment efficacy, enabling new tools to assess the efficacy of tumor treatment.
A recent study published in 2018 built an imaging-omics model to assess the efficacy of immunotherapy. The results show that this model is important for future screening of sensitive populations for immunotherapy and can dynamically assess the evolution of tumors during immunotherapy. In this model, the survival of patients with high PD-1/PD-L1 scores was significantly different from those with low scores, with median survival of 24.3 months and 11.5 months, respectively.
Nuclear medicine imaging techniques
This is a functional imaging technique, that is, rather than assessing tumor changes morphologically after treatment, it reflects how the tumor has changed functionally after treatment. With the rapid development of functional imaging techniques, it has been used in recent years in gastric cancer.
For example, by looking at radionuclide aggregation in HER2, it is possible to show HER2 expression in gastric cancer tissue in real time. The assessment of the HER2 profile, especially after treatment, is largely consistent with pathological findings and can be a guide for treatment selection after first-line anti-HER2 targeted therapy.
Summary
The evaluation of the efficacy of gastric cancer therapy is becoming increasingly rich, from morphological to functional, and from macroscopic to microscopic, with more comprehensive and precise means of assessing gastric cancer treatment. However, these new tools are not yet perfect; for example, there are still bottlenecks in the development of quantitative imaging techniques, and more research is still needed to figure out when to evaluate and the pattern of changes in different time periods because of insufficient data accumulation. It is believed that as the research progresses, the means of assessing the efficacy of gastric cancer will be improved day by day. (This article is based on a report by Professor Shen Lin from Peking University Cancer Hospital at the CSCO 2018 meeting)