Although there were some differences in hygienic, social and religious practice , PC, mostly squamous cell carcinoma , was still a rare disease over the past decades [16–18]. In most developed areas, the incidence of PC was even decreasing gradually [19, 20]. However, due to uncommon clinical cases and lack of reliably prognostic tools in assessment, clinicians seemed to have limited method in understanding and predicting the prognosis of PC.
As a tool for predicting patients’ prognosis, nomogram was widely used in oncology, such as bladder cancer, prostatic cancer and breast cancer [21–23]. Its capability was to provide a more individualized prognostic assessment for patients by combining various prognostic risk factors which had been widely recognized . Our prognostic nomogram was based on the database of SEER, which had collected the detailed information of approximately 34.6 percent of the U.S. population .
In our study, elderly patients, especially those older than 80, would have a significantly lower 3-year (34.6%, 95% CI, 27.9%-42.7%) and 5-year (23.5%, 95% CI, 16.4%-33.7%) survival (P < 0.0001). Simultaneously, these patients were also weighted more points than others. Kaplan-Meier curve of age showed that only slight difference in OS could be found among all groups under 70 (643/1188 of development group). These evidences proved that elder age might be an independent risk factor for the prognosis of PC patients, which was consistent with most studies .
According to the study by Sharma et al., black males who were suffered from PC would have a worse OS . In addition, Slopnick et al. declared that African-American PC patients probably had a higher risk of death compared with the white . However, in our study, both in the result of cox regression and Kaplan-Meier curve, no significant difference was found in the comparison among white, black and other races. This might be helpful to explore the real answer of higher mortality rate in some areas, instead of the superiority of race.
Furthermore, results of cox regression analyses also suggested the importance of cancer stage in the prognostic evaluation of patients. But it seemed to be not significant among some subgroups, including stage T1a, stage T1b and stage T1NOS. Similar to most studies, lymph node involvement and distant metastasis remained independent risk factors for patients’ prognosis .
The recent guideline on PC from European Association of Urology strongly affirmed the importance of strict grade in pathological assessment . Aita et al. claimed that high histopathological grade was responsible for a poor prognosis based on a study with an average follow-up more than 3 years involving 163 PC patients . Other studies also emphasized the importance of pathologic grade [31, 32]. But, in our study, it seemed that the histopathological grade played a different role in the assessment of patients’ prognosis except for the grade III. However, for Grade IV, only 14 (0.8%) patients were included, which might cause a statistical bias.
Above all, some limitations in our study must be taken into consideration. Firstly, the SEER database was a retrospective resource library including patients over a long period span, which might lead to an inevitable bias. Secondly, data about habit, custom (especially for sexual activity), human papilloma virus infection, average income, religion, smoking, education, Charlson comorbidity index and other information could not be available in the SEER database, which could also affect the quality of our results. Finally, no additional data of PC patients from other sources or institutions could be used for external verification, which might cause a selected bias.