Immunohistochemical and clinical characterization of the basal-like subtype of invasive breast carcinoma.
OBJECTIVE
Expression profiling studies classified breast carcinomas into estrogen receptor (ER)+/luminal, normal breast-like, HER2 overexpressing, and basal-like groups, with the latter two associated with poor outcomes. Currently, there exist clinical assays that identify ER+/luminal and HER2-overexpressing tumors, and we sought to develop a clinical assay for breast basal-like tumors.


METHODS
To identify an immunohistochemical profile for breast basal-like tumors, we collected a series of known basal-like tumors and tested them for protein patterns that are characteristic of this subtype. Next, we examined the significance of these protein patterns using tissue microarrays and evaluated the prognostic significance of these findings.


RESULTS
Using a panel of 21 basal-like tumors, which was determined using gene expression profiles, we saw that this subtype was typically immunohistochemically negative for estrogen receptor and HER2 but positive for basal cytokeratins, HER1, and/or c-KIT. Using breast carcinoma tissue microarrays representing 930 patients with 17.4-year mean follow-up, basal cytokeratin expression was associated with low disease-specific survival. HER1 expression was observed in 54% of cases positive for basal cytokeratins (versus 11% of negative cases) and was associated with poor survival independent of nodal status and size. c-KIT expression was more common in basal-like tumors than in other breast cancers but did not influence prognosis.


CONCLUSIONS
A panel of four antibodies (ER, HER1, HER2, and cytokeratin 5/6) can accurately identify basal-like tumors using standard available clinical tools and shows high specificity. These studies show that many basal-like tumors express HER1, which suggests candidate drugs for evaluation in these patients.
Genetic Pathology Evaluation Centre, University of British Columbia, Vancouver Hospital & British Columbia Cancer Agency, Vancouver, British Columbia, Canada.
Torsten O
TO
Nielsen
Forrest D
FD
Hsu
Kristin
K
Jensen
Maggie
M
Cheang
Gamze
G
Karaca
Zhiyuan
Z
Hu
Tina
T
Hernandez-Boussard
Chad
C
Livasy
Dave
D
Cowan
Lynn
L
Dressler
Lars A
LA
Akslen
Joseph
J
Ragaz
Allen M
AM
Gown
C Blake
CB
Gilks
Matt
M
van de Rijn
Charles M
CM
Perou
D014408:Biomarkers, Tumor / Q000032:analysis; D001943:Breast Neoplasms / Q000145:classification / Q000235:genetics / Q000401:mortality / Q000473:pathology*; D005260:Female; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods; D007633:Keratins / Q000032:analysis; D009361:Neoplasm Invasiveness; D018295:Neoplasms, Basal Cell / Q000235:genetics / Q000401:mortality / Q000473:pathology*; D020411:Oligonucleotide Array Sequence Analysis; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000032:analysis / Q000235:genetics; D011960:Receptors, Estrogen / Q000032:analysis / Q000235:genetics; D016019:Survival Analysis
D014408:Biomarkers, Tumor; D007633:Keratins; D018719:Erb-b2 Receptor Tyrosine Kinases; D011960:Receptors, Estrogen