Prognostic nomogram for overall survival in breast invasive micropapillary carcinoma integrating LODDS and treatment factors: A SEER-based study

Invasive micropapillary carcinoma (IMPC) of the breast is a rare and aggressive histologic subtype characterized by frequent lymph node metastasis and poor prognosis. The conventional American Joint Committee on Cancer (AJCC) tumor-node-metastasis (TNM) staging system does not account for treatment modalities or advanced nodal metrics such as the log odds of positive lymph nodes (LODDS), which may limit prognostic accuracy. This study aimed to develop and internally validate a nomogram integrating clinicopathologic characteristics, treatment variables, and LODDS to predict overall survival (OS) in breast IMPC. Clinicopathologic and survival data from 1,105 patients diagnosed between 2010 and 2015 were obtained from the Surveillance, Epidemiology, and End Results (SEER) database. The entire cohort was used for model development, with bootstrap resampling for internal validation. Least absolute shrinkage and selection operator (LASSO) regression and multivariable Cox analysis were used for variable selection and nomogram construction. Model performance was assessed using the optimism-corrected concordance index (C-index), calibration plots, time-dependent area under the receiver operating characteristic curve (AUC), decision curve analysis (DCA), and clinical impact curves (CICs), while incremental value over the AJCC TNM system was evaluated by net reclassification improvement (NRI) and integrated discrimination improvement (IDI). Ten prognostic factors were retained in the nomogram: age, tumor size, LODDS, marital status, tumor grade, M stage, rural/urban residence, molecular subtype, radiotherapy, and chemotherapy. The nomogram showed superior discrimination to TNM staging, with better optimism-corrected C-index and 3-, 5-, and 10-year AUCs (all p < 0.05), significant improvements in NRI and IDI (all p < 0.001), excellent calibration, and greater net clinical benefit on DCA and CICs. Exploratory risk stratification identified high- and low-risk groups with significantly different survival outcomes (log-rank p < 0.001). This nomogram may improve prognostic assessment in breast IMPC, although the risk stratification remains exploratory and requires external validation before clinical application.