[125] Invasive Micropapillary Breast Carcinoma Is a Lymphotropic Entity That Belongs to the Luminal Group. A Phenotypic, Chromogenic In Situ Hybridization and Retrospective Study of 164 Cases

F Bibeau, H Frugier, F Mishellany, G Mac Grogan, M Lacroix-Triki, F Penault-Llorca, M Antoine, V Becette, P Berteau, F Boissiere-Michot. CRLC Val d'Aurelle, Montpellier, France; Centre Jean Perrin, Clermont-Ferrand, France; Institut Bergoni, Bordeaux, France; Institut Claudius Regaud, Toulouse, France; Hopital Tenon, Paris, France; Centre Rene Huguenin, Saint-Cloud, France; Hopital Saint-Louis, Paris, France

Background: Invasive micropapillary breast carcinoma (IMBC) is an aggressive variant of breast cancer, characterized by a specific insideout pattern and lymphotropic propensity. The phenotypic and molecular categories in which IMBC could be included are still subject of investigation.
Design: The aim of our study was to assess the pathologic features of 164 IMBC and to specify their phenotype by immunohistochemistry (IHC) on tissue-microarray. IHC was performed with the following markers: (i) luminal: Estrogen and Progesterone receptors (ER, PR), cytokeratins (CK)7, CK8-18; (ii) HER2 (HER2 chromogenic in situ hybridization (CISH) on any HER2 immunoreactive case); (iii) basal/ myoepithelial: CK5/6, CK14, EGFR, vimentin, CD117; p63, SMA, S100; (iv) others: Epithelial membrane antigen (EMA), Ki67.
Results: Multifocality was observed in 21% of IMBC. IMBC were pure, predominant (>50%) or focal (<50%) in 50, 32 and 18% of the cases, respectively. SBR grades II, III and I were observed in 66, 29 and 9% of IMBC, respectively. Despite a majority of pT1 stage (63%), 66% of IMBC displayed lymph node invasion and 70% had lymphatic invasion. All tumor cell clusters showed a typical EMA peripheral staining. A luminal phenotype with no basal marker expression was observed in 83% of IMBC, of which 15% presented a Ki67 immunostaining 20%. HER2 amplification was observed in 12% of IMBC, surprisingly associated in 5 cases with an incomplete membrane immunostaining. Two percent of IMBC had a basal phenotype (ER-, PR- , HER2 non amplified, basal markers +), while 3% of IMBC were triple negative and did not express basal markers. No myoepithelial marker was expressed.
Conclusions: IMBC mainly belongs to the luminal group and is an agressive entity, with a high proportion of lymphatic and lymph node invasion. In order not to miss patients who would benefit from trastuzumab therapy, assessment of HER2 gene status should be performed in all IMBC, due to the peculiar HER2 immunoreactivity associated with amplification in this special type of breast cancer.
Category: Breast

Monday, March 9, 2009 1:00 PM

Poster Session II # 30, Monday Afternoon