The precision medicine initiative launched by President Obama in 2015 was an epoch-making proposal designed to bring about personalized medicine and optimized medicine. The first applications of the precision medicine initiative that come to mind in the field of gastroenterology are cancer and inflammatory bowel disease. This concept has already begun to permeate other fields, including diabetes mellitus and nutrition.

The best treatment currently available for resectable cancer is to remove all of the cancer by means of surgery. In the case of unresectable cancer, on the other hand, radiotherapy and anticancer chemotherapy are often selected. There are standard therapies among the various anticancer chemotherapies available, and in many cases, those that are more effective than other therapies are regarded as first-line standard therapy. However, while many patients respond to standard therapy, it is also true that there will always be a certain segment of patients with a poor response. Worded differently, one could say that the standard therapy is aimed at the majority of responders and disregards non-responders. Precision medicine abandons the concept of standard therapy and promotes cancer genomic profiling-dependent therapy. First, comprehensive genomic profiling (CGP) is performed, and therapy that is effective for the genetic mutation caused in the cancer in individual patients is then selected. If the standard therapy is known to be effective, the standard therapy can be performed, and if a therapy other than the standard therapy is known to be effective, the therapy that is suitable for the patient can be selected.

In Japan, the FoundationOne® CDx Cancer Genomic Profile and the OncoGuide™ NCC Oncopanel System have been covered by insurance since June 2019. The FoundationOne® Liquid CDx Cancer Genomic Profile was added to that list in August 2021, and an approval application was submitted for the TruSight™ Oncology Comprehensive Panel System in May 2022. Considering the fact that the cost of CGP before being covered by insurance was 550,000 yen, many more patients should now be able to benefit from CGP.

Cancer begins as a trunk mutation, and branch mutations occur and acquire drug resistance with use of anticancer agents. If that is the case, CGP should be performed first, and the best therapy should be performed. It would be extremely rational to perform CGP periodically thereafter to exhaustively pursue genetic mutations, and if a specific mutation appears, to perform therapy with a drug that corresponds to that mutation. As liquid biopsy using blood, etc., appears to be suitable for observing mutations over time in this manner, it may become the mainstay of CGP going forward. If the cancer is one with few branch mutations, earlier therapy would be possible with early detection of mutations by a more sensitive method such as digital PCR and rapid initiation of therapy rather than CGP, which targets only specific gene mutations of individual cancers revealed by CGP.

However, CGP is covered by insurance only once in a lifetime per cancer under Japan’s insurance system. In other words, the ideal use of CGP mentioned above is realistically impossible. Considering the fact that CGP is an expensive test, there may be a limit to how far one can pursue an ideal under Japan’s healthcare system. In addition, there are institutional standards that need to be met for hospitals to be able to perform precision medicine, and there are only about 230 such hospitals in Japan. Precision medicine cannot be performed at any other hospitals. One has to visit one of the 230 hospitals in Japan to be able to undergo precision medicine.

It is common knowledge among those practicing diagnostic imaging that macroscopic imaging findings (ultrasound images, CT, MRI) reflect microscopic imaging findings (pathological specimens). In other words, a final decision is made while conjuring up a histopathological image when performing diagnostic imaging. A histopathological image is an arrangement of various cells, blood vessels, lymphatic vessels, and lymph nodes, etc., characteristic to each disease. And that arrangement is reflected in the macroscopic image.

For example, we know that the proportion of lymphocytic infiltration in cancer tissue is high and that enlargement of surrounding lymph nodes is often seen in certain types of cancer that respond to immune checkpoint inhibitors (ICIs). In addition, blood flow is often abundant. These are changes that could show up in imaging findings. If ultrasonography is used, it is easy to diagnose enlargement of lymphatic tissue surrounding a tumor. Abundant blood flow can be detected using Doppler ultrasound. In other words, cancer that responds to ICIs can be predicted with ultrasonography.

ICIs are just one example, but identifying macroscopic imaging findings indicative of the effectiveness of drugs other than ICIs is useful from at least the following two standpoints. One is the ability to provide treatment after selecting a drug that is effective for the cancer based on the characteristic macroscopic images. Another is the ability to reveal the effectiveness of another drug in cases where imaging indicates the occurrence of a pathognomonic change while treating a patient with a certain anticancer chemotherapy agent.

Furthermore, the number of cancer patients who cannot receive accurate cancer therapy may increase at the hospitals that can provide only the conventional standard therapy, unlike the approximately 230 hospitals in Japan that can provide precision medicine. For cancer patients, ultrasonography is a modality that can be performed repeatedly with very little invasiveness. If ultrasonography-based diagnosis and treatment of cancer similar to the above-mentioned liquid biopsy becomes a reality, ultrasound will likely be able to contribute greatly to precision medicine.

If we can rack our brains to link ultrasound and precision medicine without thinking it impossible or futile, the future of medical ultrasonics will be bright.