Nationwide survey on HER2 and PD-L1 testing practices in gastric cancer across Japan

Since HER2 and PD-L1 testing are key to selecting drugs for first-line treatments in advanced gastric cancer, evaluating differences in these tests among institutions is necessary to standardize treatment.

A questionnaire survey was conducted targeting institutions certified by the Japanese Gastric Cancer Association.

Responses were obtained from 155 institutions. Most institutions performed HER2 testing in-house, while PD-L1 tests were largely outsourced. HER2 scores and PD-L1 CPS rates showed greater variability across institutions than anticipated. In the pre-analytic phase, 10% neutral buffered formalin was commonly used, with fixation practices generally following guidelines. Overall, the impact of fixation-related factors was limited, but in surgical specimens, longer fixation was associated with a higher proportion of score 0/1+ and a lower proportion of score 3+. When examining HER2 scores by institution, if a particular score had a high (or low) frequency in biopsy, the same trend was also seen in surgical specimens.

These findings suggest that not only factors related to specimen preparation, but also biases in evaluation criteria among pathologists may contribute to the significant variability among institutions. Standardization of pre- and post-analytic phases, coupled with appropriate training, is essential to achieve consistent gastric cancer therapy.