Triple negative breast cancer: a study from the point of view of basal CK5/6 and HER-1.
OBJECTIVE
Basal-like breast tumours, as defined by microarrays, carry a poor prognosis and therapeutic options are limited to date. Often, these tumours are defined as oestrogen receptor (ER) negative/progesterone receptor (PR) negative/human epidermal growth factor receptor 2 (HER-2) negative (triple negative) by immunohistochemistry (IHC), but a more complete definition should include expression of basal cytokeratins (CK5/6, CK14 or CK17) and/or human epidermal growth factor receptor 1 (HER-1). The aim of this study was to investigate to what extent CK5/6 and HER-1 characterise the group of triple negative breast cancers.


METHODS
Expression of CK5/6 and HER-1 was studied by IHC in 25 triple negative breast carcinomas and 32 grade-matched, non-triple-negative controls. All 57 cases were further subjected to fluorescence in situ hybridisation to investigate HER-1 gene copy number.


RESULTS
CK5/6 and HER-1 expression was most frequent in triple negative tumours: 22 out of 25 cases (88.0%) expressed at least one of these markers (60.0% CK5/6 positive and 52.0% HER-1 positive). In the control group, CK5/6 and HER-1 expression was found in ER-negative but not in ER-positive tumours (ER negative/PR negative/HER-2 positive tumours: 20.0% CK5/6 positive and 46.7% HER-1 positive). HER-1 gene amplification was found in five cases only: four triple negative (16.0%) and one ER-negative control (ER negative/PR negative/HER-2 positive, 6.7%). Of interest, all five HER-1 amplified cases showed a remarkably homogeneous HER-1 expression pattern.


CONCLUSIONS
Expression of CK5/6 and HER-1 is frequent in ER-negative breast cancers, in triple negative and in non-triple negative tumours. In a minority of cases, HER-1 overexpression may be caused by HER-1 gene amplification. Further studies are needed to investigate whether such cases might benefit from anti-HER-1 therapy.
Pintens
S
S
Department of Pathology, UZ Leuven, Leuven, Belgium.
Neven
P
P
Drijkoningen
M
M
Van Belle
V
V
Moerman
P
P
Christiaens
M-R
MR
Smeets
A
A
Wildiers
H
H
Vanden Bempt
I
I
D014408:Biomarkers, Tumor / Q000378:metabolism*; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism*; D066246:ErbB Receptors / Q000235:genetics / Q000378:metabolism; D005260:Female; D005784:Gene Amplification; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D053555:Keratin-5 / Q000378:metabolism; D053553:Keratin-6 / Q000378:metabolism; D009363:Neoplasm Proteins / Q000378:metabolism*; D011960:Receptors, Estrogen / Q000378:metabolism; D011980:Receptors, Progesterone / Q000378:metabolism
D014408:Biomarkers, Tumor; D053555:Keratin-5; D053553:Keratin-6; D009363:Neoplasm Proteins; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; C512478:EGFR protein, human; D066246:ErbB Receptors