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Pearls of wisdom from Professor Dr Tan Puay Hoon

We had some interesting cases shown to Prof Dr Tan PH from SGH, and received a nice tutorial from her in return :).

1. Papillary lesion

In a papillary lesion, one should use more than one myoepithelial marker.  The myoepithelial markers potpourri: p63, HMWCK (either CK 5/6 or CK14), SMA.

Pitfall in papillary lesion: secretory cells may have aberrant p63 expression.

Neoplastic (and suspicious) papillary lesion will exhibit clonal proliferation.  ER is preferably used: diffuse positivity will suggest clonal proliferation, whereas intraductal papillomas will usually exhibit patchy ER positivity.  PR may be used in conjunction with ER but the staining is more heterogeneous, therefore it may be confusing to identify clonal proliferation by using PR immunohistochemical stain.

HER-2 immunohistochemical stain is used only if there is invasive disease, and not really used to establish clonality.

Encapsulated papillary carcinoma is more expansile and bulging compared to intraductal papillary carcinoma (synonym for intraductal papillary carcinoma: papillary DCIS).

2. Phyllodes vs cellular fibroadenoma

Both are fibroepithelial lesions.

Phyllodes tumour must have well-developed and stroma-bulging leaf-life formation or fronds.

Young patients will have more cellular breast stroma, therefore must be careful of diagnosing phyllodes tumour in these patients.

Stromal atypia must be seen in phyllodes tumour.

Mitosis:
-younger patients with fibroadenoma may have higher mitotic figures compared to older patients, so one must keep that in mind before diagnosing a young patient with phyllodes tumour.
- if in core biopsy, 2 or more mitosis is significant.  When present with stromal atypia and hypercellularity, may suggest malignant -- but not enough criteria so comment about need excision for definitive diagnosis.

Margins: fibroadenoma will exhibit circumscription or rimming.  Extension into surrounding fat suggests phyllodes tumour.

Our case suggests more of cellular fibroadenoma but extension into surrounding fat was seen.  Therefore have to comment about this in the report, and advise follow-up.

3.  Cavity re-excision of breast (post core or excision biopsy of a malignancy).

Ducts surrounding the cavity may exhibit squamous metaplasia, therefore myoepithelial cells may not be present (a diagnostic pitfall!)
However benign ducts will maintain in lobular formation.
Therefore haphazard ducts that do not exhibit lobular formation will be suggestive of malignancy.
Must compare with previous biopsy.

4. To diagnose as classical or even atypical medullary carcinoma, the breast lesion needs a prominent lymphoplasmacytic surrounding.

If there is no prominent lymphoplasmacytic surrounding, one may need to consider another diagnosis like infiltrating ductal carcinoma.

5.  HER-2 DDISH or FISH is usually done on equivocal cases (HER-2 2+), and not on negative or positive cases.

However one may make an exception when:
 - the material is from outside centre
- the material is not well-fixed
- immunohistochemical staining for HER-2 is not precisely delineating the cell membrane.

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