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[384] Polysomy of chromosome 17 in breast cancer with c-erbB2 [Her-2] overexpression: a study of 179 cases using fluorescence in situ hybridization (FISH).
Abstract 384 provides:
Introduction. The HER2/neu protooncogene located at 17q12-21 is overexpressed in 25-30% breast cancers and it is known that confers important prognosis and predictive value. The overexpression of this growth factor receptor is mostly caused by HER2/neu gene amplification in >90% of breast cancers. There are different methods to evaluate c-erbB2 overexpression/amplification but immunohistochemistry (IHC) and FISH are the most used. IHC and FISH have shown discordances in cases with increased chromosome 17 copy number per cell. Chromosomal aneusomy either monosomy or polysomy is frequently observed in breast carcinoma. However it is unclear whether polysomy 17 may play a role in HER2/neu gene dosage and c-erbB2 overexpression.
Aims. We analyzed polysomy of chromosome 17 to know the contribution of this aberration to c-erbB2 overexpression especially in cases with low levels of overexpression (IHC 2+).
Patients and Methods. We present a series of 179 patients studied prospectively in whom we performed IHC with Herceptest (DAKO) and FISH with PathVysion probe (Vysis) essentially in cases with score 2+ by IHC (113 patients).
Results. Among 179 patients we observed 12% (21/179) of polysomy 17. We found that 15% (17/113) of cases with IHC 2+showed polysomy 17. Cases with chromosome 17 polysomy have increased HER2 gene copies but true gene amplification is presented only in 4% (7/179) of patients. We did not find different polysomy 17 distribution in cases with or without amplification (Table 1).
Conclusions.
-FISH analysis permits the confirmation of HER2/neu gene amplification.
-Polysomy 17 was more frequently found in cases scored 2+ by IHC.
-It is necessary to study in depth the clinical significance of polysomy 17.
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