Study design

This retrospective study was approved by the Ethics Committee of Hirosaki University (approval number: 2021‐089). Because all participants had previously provided written informed consent for other biomarker studies, the Ethics Committee waived informed consent for our study.

We conducted our study between June 21 and November 1, 2021. The cohort comprised 60 healthy controls (Ctrl group), 57 patients with UC (UC group), and 57 patients with RCC (RCC group) who had received their second dose of the BNT162b2 vaccination at least 7 days before measuring the titer of anti‐SARS‐CoV‐2 antibodies. The Ctrl group included members of the medical staff and medical students at Hirosaki University Hospital. Those with previous SARS‐CoV‐2 infection or blood samples taken less than 7 days after the second BNT162b2 dose were excluded. Blood samples were collected cross‐sectionally and active anticancer treatment was defined at the time of first vaccination. Clinical parameters, such as age, sex, types of anticancer therapy, metastatic disease, and the concomitant use of steroids, were obtained from medical records.