During the last two decades, imaging in drug development has been greatly advanced in a diversity of
    therapeutic fields, especially in the oncology field. As regulatory agencies seek robust evidence for
    primary endpoints, as much as possible, medical imaging usage is rapidly increased to support the
    primary endpoints in clinical trials.

  The addition of medical imaging in the clinical trials requires logistical and technical considerations, as
    follows: (1) selection of appropriate qualified imaging biomarker, (2) standardization of imaging
    acquisition, archive, and analysis, (3) independent blinded image review, and (4) system for complex
    workflow and regulatory compliance.

  In 2018, US FDA issued “Clinical Trial Imaging Endpoint Process Standards Guidance for Industry” so that
    pharmaceutical companies, imaging scientists, and clinical trial professionals can utilize imaging in a
    clinical trial as an appropriate manner.

  In the clinical trial of oncology, the RECIST 1.1 is the most widely used as qualified biomarkers based on
    anatomical medical imaging, is adapted as a primary endpoint by the FDA (21). Nevertheless, RECIST 1.1
    has its own limitation in treatment response assessment, specifically in the brain tumor, lymphoma,
    and bone lesions. The NCI’s Cancer Imaging Program, therefore, allows to utilize other various
    imaging response criteria as summarized in Table 1.

  In the era of immunotherapy for cancer treatment, the number of clinical trials for cancer
    immunotherapeutic agents has been rapidly increasing.

  In 2017, the RECIST Working Group released a consensus guideline "iRECIST" for internationally
    standardized response assessment in multicenter trial. The iRECIST was developed based on RECIST 1.1,
    additionally introducing new terminologies and criteria. Accordingly, iRECIST is good for standardized
    response assessments but also requires cautions to follow.