Background: Our study aimed to assess the prognostic value of poorly differentiated clusters (PDCs) in invasive breast cancer.
Methods: A total of 146 cases of operable invasive ductal carcinoma that was not otherwise specified (IDC-NOS), from 2002 to 2009, were pathologically reviewed. Cancer clusters with five or more cancer cells and lacking gland-like structures were counted from a field containing maximum clusters in H & E slides under a×20 objective lens (0.950 mm2 field of vision).
Results: Tumors with <5, 5 to 9, and ≥10 clusters were graded as G1, G2, and G3, respectively (n=41, 60, and 45 tumors, respectively). An interobserver test showed good reproducibility, with a Cohen's kappa coefficient of 0.739. The PDC grade was significantly associated with N stage (P<0.001), lymphovascular invasion (P=0.007), tumor budding grade (P<0.001), relapse rate (P<0.001), and death rate (P<0.001). Survival analyses revealed that the PDC grade was a significant prognostic factor for disease-free survival (hazard ratio 3.811; P<0.001) and overall survival (hazard ratio 3.730; P=0.001), independent of T stage, N stage, or tumor budding grade.
Conclusions: The PDC grade is an independent prognostic factor of IDC-NOS. Considering the simplicity and availability of this method relative to conventional clinical pathology, PDCs may serve as a novel prognostic histological characteristic in IDC-NOS.