Specific morphological features predictive for the basal phenotype in grade 3 invasive ductal carcinoma of breast

TLDR

CK14 expression marks a subset of grade 3 invasive ductal carcinomas with distinct metastatic behavior and clinical outcomes, yet routine pathology lacks morphological criteria for their identification. The study aimed to identify histological characteristics that predict the basal phenotype in CK14‑positive grade 3 invasive ductal carcinomas. Researchers reviewed 453 grade 3 IDCs, scored 88 CK14‑positive cases using a standardized tick‑box proforma, and applied logistic regression to determine predictors of the basal phenotype. Analysis revealed that central scar, tumor necrosis, spindle cells or squamous metaplasia, high mitotic count (>40/10 HPF), and high nuclear‑cytoplasmic ratio were strong predictors of the basal phenotype, with interobserver agreement ranging from fair to good.

Abstract

Cytokeratin (CK) 14, a myoepithelial marker, is also expressed in a proportion of breast carcinomas. There is evidence that these tumours show a differing metastatic pattern and clinical outcome from other invasive ductal carcinomas (IDCs) and may need different management. Currently, they are not identified in routine practice and no morphological guidelines exist to aid their identification. The aim of this study was to analyse the histological features of CK14+ IDC.A detailed histological review of 453 grade 3 IDCs revealed 88 (19.4%) that expressed CK14. Assessment was made independently by two pathologists using a standardized 'tick-box' proforma covering grade, architectural and cytological features. The results were analysed using logistic regression to identify features that predicted for basal phenotype. Concordance between the two pathologists was fair to good for most parameters (kappa 0.4-0.6). On multiple logistic regression, the basal phenotype was highly significantly associated with the presence of a central scar (P = 0.005), tumour necrosis (P < 0.0001), presence of spindle cells (P = 0.006) or squamous metaplasia (P < 0.0001), high total mitotic count (> 40 per 10 high-power field) (P = 0.0002) and high nuclear-cytoplasmic ratio (P = 0.0002).Specific morphological features are strongly associated with basal-like breast carcinoma. These could be used in routine diagnostic practice to identify this important subset of tumours.