New Staging System and Prognostic Model for Malignant Phyllodes Tumor Patients without Distant Metastasis: A Development and Validation Study

SIMPLE SUMMARY: Malignant phyllodes tumor of the breast (MPTB) is a rare fibroepithelial tumor. Because of its rarity, research based on large clinical datasets is currently lacking. Moreover, the prognostic factors of MPTB have yet to be determined. Prognostic models and staging systems for MPTB patients are needed, but are also lacking. Here, we conducted a comparison between MPTB cases and invasive ductal carcinoma cases. Our findings reveal substantial differences in the clinical features of invasive ductal carcinoma and MPTB. We applied the KAPS algorithm to explore and establish a new stage- and age-stratification system. The system exhibited a good prognostic stratification ability for both the internal cohort and the external cohort. Furthermore, we developed independent prognostic models for MPTB using Cox proportional hazards regression and random survival forests (RSF). Finally, we built a user-friendly web app to allow researchers and doctors to access our model. ABSTRACT: Purpose: To build a new staging system and new prognostic models for MPTB. Methods: We performed a comprehensive analysis of the data from the SEER database. Results: We discussed the characteristics of MPTB by comparing 1085 MPTB cases with 382,718 invasive ductal carcinoma cases. We established a new stage- and age-stratification system for MPTB patients. Furthermore, we built two prognostic models for MPTB patients. The validity of these models was confirmed through multifaceted and multidata verification. Conclusions: Our study provided a staging system and prognostic models for MPTB patients, which can not only help to predict patient outcomes, but also enhance the understanding of the prognostic factors associated with MPTB.