Prognostic impact of tumor‑associated stroma in triple-negative breast cancer.

Aim: To establish the histological categorization of tumor‑associated stroma (TAS) that reflects the biological behavior of triple-negative breast cancer (TNBC).

Methods and results: One-hundred-and-twenty surgically resected cases of TNBC were examined. We histologically categorized the TAS in the invasive frontal region into two groups: mature stroma (MS) and immature stroma (IS). The designation of IS was applied for tumors in which the largest myxoid stroma filled a high-power magnification field. When there were no myxoid stroma that meet the criteria for IS, TAS was categorized as MS. The tumors with type MS were observed in 103 (85.8%) of patients, whereas 17 (14.2%) of patients had tumors with IS. In total, 72 out of 120 patients with TNBC exhibited high tumor-infiltrating lymphocytes (TILs) representing 60% of the cohort. The incidences of high TILs were 66% (68 out of 103) in the MS group but only 23.5% (4 of 17) in the IS group (p = 0.001). Progression-free survival (PFS) and overall survival (OS) curves were different between IS and MS groups (p < 0.001 each), and Cox multivariate regression analysis revealed that IS was an independent indicator for lower PFS and OS rates (p < 0.001; p = 0.008).

Conclusion: Our findings suggest that TAS characteristics, particularly the distinction between IS and MS, play a significant role in the prognosis of TNBC. The presence of IS, associated with poor prognosis and low TILs, contrasts with the favorable outcomes observed in cases with MS. Understanding these TAS dynamics could aid in identifying patients with varying prognostic outcomes in TNBC, necessitating further research into the mechanisms behind these observations.