Invasive Micropapillary Carcinoma of the Breast
Definition
- Breast carcinoma with a prominent (pseudo) micropapillary pattern
Diagnostic Criteria
- 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
- 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
