Invasive Micropapillary Carcinoma of the Breast

Definition

Numerous small pseudo-papillary clusters of cells
- No fibrovascular cores
- Frequent central lumen formation in clusters
- Peripherally located nuclei frequently bulge out with knobby appearance, "the hedgehog" tumor
Clusters surrounded by clear spaces
- One or only a few clusters per space
- Scant mucin rarely detectable in spaces
Spaces surrounded by loose fibrocollagenous stroma
Frequent high nuclear grade reported in some series
Frequently has abundant eosinophilic cytoplasm
Frequent lymphatic involvement
Occasional psammoma bodies
Associated DCIS may be of various types
- Not related to micropapillary DCIS
Pattern may be predominant or focal
- No clinical difference between predominant and focal cases
- No reported cutoff for minimal significant amount of pattern
- Report such cases as mixed
Frequently mixed with infiltrating ductal carcinoma
- Rarely mixed with other type

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