A modified clinicopathological tumor staging system for survival prediction of patients with penile cancer

Background The 8th American Joint Committee on Cancer tumor–node–metastasis (AJCC-TNM) staging system is based on a few retrospective single-center studies. We aimed to test the prognostic validity of the staging system and to determine whether a modified clinicopathological tumor staging system that includes lymphovascular embolization could increase the accuracy of prognostic prediction for patients with stage T2–3 penile cancer. Methods A training cohort of 411 patients who were treated at 2 centers in China and Brazil between 2000 and 2015 were staged according to the 8th AJCC-TNM staging system. The internal validation was analyzed by bootstrap-corrected C-indexes (resampled 1000 times). Data from 436 patients who were treated at 15 centers over four continents were used for external validation. Results A survivorship overlap was observed between T2 and T3 patients ( P = 0.587) classified according to the 8th AJCC-TNM staging system. Lymphovascular embolization was a significant prognostic factor for metastasis and survival (all P < 0.001). Based on the multivariate analysis, only lymphovascular embolization showed a significant influence on cancer-specific survival (CSS) (hazard ratio = 1.587, 95% confidence interval = 1.253–2.011; P = 0.001). T2 and T3 patients with lymphovascular embolization showed significantly shorter CSS than did those without lymphovascular embolization ( P < 0.001). Therefore, a modified clinicopathological staging system was proposed, with the T2 and T3 categories of the 8th AJCC-TNM staging system being subdivided into two new categories as follows: t2 tumors invade the corpus spongiosum and/or corpora cavernosa and/or urethra without lymphovascular invasion, and t3 tumors invade the corpus spongiosum and/or corpora cavernosa and/or urethra with lymphovascular invasion. The modified staging system involving lymphovascular embolization showed improved prognostic stratification with significant differences in CSS among all categories (all P < 0.005) and exhibited higher accuracy in predicting patient prognoses than did the 8th AJCC-TNM staging system (C-index, 0.739 vs. 0.696). These results were confirmed in the external validation cohort. Conclusions T2–3 penile cancers are heterogeneous, and a modified clinicopathological staging system that incorporates lymphovascular embolization may better predict the prognosis of patients with penile cancer than does the 8th AJCC-TNM staging system. Trial registration This study was retrospectively registered on Chinese Clinical Trail Registry: ChiCTR16008041 (2016-03-02). http://www.chictr.org.cn