Histiocytoid Carcinoma of the Breast

Definition

Abundant finely vacuolated cytoplasm
- Amphophilic to faintly eosinophilic
- May appear granular
- PASd may show granular cytoplasmic mucin stain
Indistinct cell borders
Uniform, low grade small nuclei
- Small nucleoli
- Mitotic count generally 1-2/10 hpf
Intracytoplasmic lumens rare to frequent
- Highlighted by Alcian Blue or EMA stains
- May result in areas with signet ring appearance
- PASd may stain intralumenal mucin
Frequent single file and targetoid infiltrative pattern
Frequent central hyaline fibrosis
Fat frequently invaded by single non-cohesive cells
Considered by some to represent a variant pattern of lobular carcinoma or of apocrine carcinoma, see Differential Diagnosis

Richard L Kempson MD
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342

Original posting:: May 1, 2006