Novel and efficient method for culturing patient‐derived gastric cancer stem cells

Experimental techniques for patient‐derived cancer stem‐cell organoids/spheroids can be powerful diagnostic tools for personalized chemotherapy. However, establishing their cultures from gastric cancer remains challenging due to low culture efficiency and cumbersome methods. To propagate gastric cancer cells as highly proliferative stem‐cell spheroids in vitro, we initially used a similar method to that for colorectal cancer stem cells, which, unfortunately, resulted in a low success rate (25%, 18 of 71 cases). We scrutinized the protocol and found that the unsuccessful cases were largely caused by the paucity of cancer stem cells in the sampled tissues as well as insufficient culture media. To overcome these obstacles, we extensively revised our sample collection protocol and culture conditions. We then investigated the following second cohort and, consequently, achieved a significantly higher success rate (88%, 29 of 33 cases). One of the key improvements included new sampling procedures for tumor tissues from wider and deeper areas of gastric cancer specimens, which allowed securing cancer stem cells more reproducibly. Additionally, we embedded tumor epithelial pieces separately in both Matrigel and collagen type‐I as their preference to the extracellular matrix was different depending on the tumors. We also added a low concentration of Wnt ligands to the culture, which helped the growth of occasional Wnt‐responsive gastric cancer stem‐cell spheroids without allowing proliferation of the normal gastric epithelial stem cells. This newly improved spheroid culture method may facilitate further studies, including personalized drug‐sensitivity tests prior to drug therapy. We developed a simple and efficient method to propagate patient‐derived gastric cancer stem‐cell spheroids by improving our conventional sample collection protocol and culture conditions. These spheroids can be utilized to investigate new molecular targeted therapies and their companion diagnostics for patient selection.