Novel Prognostic Staging System for Patients With De Novo Metastatic Breast Cancer

Abstract

Purpose: Given the heterogeneity and improvement in outcomes for metastatic breast cancer (MBC), we developed a staging system that refines prognostic estimates for patients with metastatic cancer at the time of initial diagnosis, de novo MBC (dnMBC), on the basis of survival outcomes and disease-related variables.

Methods: Patients with dnMBC (2010-2016) were selected from the National Cancer Database (NCDB). Recursive partitioning analysis (RPA) was used to group patients with similar overall survival (OS) on the basis of clinical T category, grade, estrogen receptor (ER), progesterone receptor, human epidermal growth factor receptor 2, histology, organ system site of metastases (bone-only, brain-only, visceral), and number of organ systems involved. Three-year OS rates were used to assign a final stage: IVA: >70%, IVB: 50%-70%, IVC: 25 to <50%, and IVD: <25%. Bootstrapping was applied with 1,000 iterations, and final stage assignments were made based on the most commonly occurring assignment. Unadjusted OS was estimated. Validation analyses were conducted using SEER and NCDB.

Results: At a median follow-up of 52.9 months, the median OS of the original cohort (N = 42,467) was 35.4 months (95% CI, 34.8 to 35.9). RPA stratified patients into 53 groups with 3-year OS rates ranging from 73.5% to 5.7%; these groups were amalgamated into four stage groups: 3-year OS, A = 73.2%, B = 61.9%, C = 40.1%, and D = 17% (log-rank P < .001). After bootstrapping, the survival outcomes for the four stages remained significantly different (log-rank P < .001). This staging system was then validated using SEER data (N = 20,469) and a separate cohort from the NCDB (N = 7,645) (both log-rank P < .001).

Conclusion: Our findings regarding the heterogeneity in outcomes for patients with dnMBC could guide future revisions of the current American Joint Committee on Cancer staging guidelines for patients with newly diagnosed stage IV disease. Our findings should be independently confirmed.

FIG 1.

Unadjusted overall survival stratified by assigned stage IVA-D (3-year survival: IVA: >70%, IVB: 50%-70%, IVC: 25% to <50%, and IVD: <25%) shown for (A) the original recursive partitioning analysis and (B) the bootstrapped analysis. Analyses on the basis of patients with de novo metastatic breast cancer, diagnosed 2010-2016, in the National Cancer Database.

FIG 2.

Unadjusted overall survival stratified by assigned stage IVA-D (assignments on the basis of recursive partitioning and bootstrapped analyses) for separate validation cohorts from (A) SEER (patients diagnosed with de novo metastatic breast cancer 2010-2018) and (B) the National Cancer Database (patients diagnosed with metastatic breast cancer 2017-2018).