S‐1 (TS‐1; Taiho Pharmaceutical Co. Ltd., Tokyo, Japan) is a third‐generation oral fluoropyrimidine antitumor agent, which combines tegafur, gimeracil, and oteracil potassium in a molar ratio of 1.0:0.4:1.0, and has been reported to be effective against various solid cancers, including gastric, colon, and non‐small cell lung cancer.2, 3, 4 Recently, a number of studies have indicated that S‐1 treatment is effective against thymic carcinoma.5, 6, 7 S‐1 plus cisplatin with concurrent radiotherapy is a commonly used treatment for non‐small cell lung cancer. Here, PSMD1 is linked to thymic carcinoma.