4.6. Limitations
ONCOLOGY
There are several limitations in our study that need to be acknowledged. First, nomograms were established using retrospective data, which is associated with potential selection and information bias. After all, it’s easy to answer “no” or “unknown” than to recall the real solution. Therefore, prospective studies should be encouraged for further research. Second, some potentially important factors were not included in the SEER database, such as the human immunodeficiency virus and Epstein–Barr virus detection, history of alcohol and tobacco consumption, LDH, Eastern Cooperative Oncology Group and ultrasonic examination, which suggests that future studies of H&NNHL need to include these meaningful factors. Third, the SEER database does not separate “no” and “unknown” status. After all, there exists difference between them. In addition, more detailed information such as extent of radiation protocols used, the specific chemotherapy regimens and usage of new treatment strategies were not included and are expected in future researches. Fourth, the AJCC staging system has reached the 8th edition, but our research was still based on the 7th edition because it’s the latest record in the SEER database. It’s also a limitation and need to be improved as the database is updated. Finally, external validation of the nomogram was not performed, using only internal validation may lead to overfitting of new models. Further researches of multi-centered, large samples, diverse clinical, biological, and histopathologic factors are expected to measure the suitability of our nomograms among general population and confirm its clinical application value. Despite such inevitable limitations, we believe that our results, to a certain extent, have important implications in examining H&NNHL epidemiology and prognostic indicators of survival.