Case of the month - October 2006
- discussion
Diagnosis - Combined mucinous & micropapillary carcinoma
- This is an unusual combined tumour composed of approximately 50% pure mucinous carcinoma and 50% micropapillary carcinoma
- The mucinous area shows typical low grade features with tumour cells floating in PAS/Diastase positive mucinous lakes. The micropapillary area shows very little staining for neutral mucin.
- Both areas are strongly ER positive
- E cadherin and Her 2 staining highlights the different membranous distribution of these antigens in the two tumour areas - see discussion of immunohistochemistry below
Pure mucinous carcinoma has a good prognosis whereas micropapillary carcinoma has a poor prognosis - in this case there were positive lymph nodes all of which showed a pattern more in keeping with an origin from the micropapillary area
The diagnosis of invasive micropapillary carcinoma rests on the recognition of the following features:
- Small micropapillary tufts of tumour cells with a central stromal core which is not vascular
- The tumour clusters lie in clear spaces bounded by a fine collagen mesh
- Tumour cells usually have abundant finely granular cytoplasm
- Cytoplasmic mucin is often demonstrable but mucin is not usually present in the surrounding clear spaces
- Calcification is inconsistent
- Nuclear atypia is moderate or severe
- Tumours of mixed (micropapillary + other) histological pattern are common
The immunoprofile in a series of 62 cases has been studied by Pettinato and colleagues:
- 100% of cases Cytokeratin +ve
- 30% of cases ER +ve
- 95% of cases Her 2 +ve (2+ or 3+)
- E cadherin staining was positive but characteristically spared the ctoplasmic membrane towards the stroma...
- we could not confirm this finding in this case although the opposite pattern was apparent in the mucinous area (see link)
For a detailed account of the genetic abnormalities seen in micropapillary carcinomas see Marchio et al 2008 (Reference 3)
Medium power view of lymph node metastasis
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