www.mdedge.com/jcso/hphemonc Hematology-Oncology Volume 12, Part 6 11
Genomic Testing in Early-Stage Breast Cancer
expression varies in intensity throughout the
cell cycle, has been used as a measurement
of tumor cell proliferation. 10 Two large meta-analyses have demonstrated that high Ki-67
expression in breast tumors is independently
associated with worse disease-free and overall
survival rates.11, 12 Ki-67 expression has also been
used to classify HR-positive tumors as luminal
A or B. After classifying tumor subtypes based
on intrinsic gene expression profiling, Cheang
and colleagues determined that a Ki-67 cut
point of 13.25% differentiated luminal A and B
tumors. 13 However, the ideal cut point for Ki-67
remains unclear, as the sensitivity and specificity in this study was 77% and 78%, respectively.
Others have combined Ki-67 with standard
ER, PR, and HER2 testing. This immunohistochemical 4 (IHC4) score, which weighs each
of these variables, was validated in postmenopausal patients from the ATAC (Arimidex,
Tamoxifen, Alone or in Combination) trial who
had ER-positive tumors and did not receive
chemotherapy. 14 The prognostic information
from the IHC4 was similar to that seen with
the 21-gene recurrence score (Oncotype DX),
which is discussed later in this article. The key
challenge with Ki-67 testing currently is the
lack of a validated test methodology and intra-observer variability in interpreting the Ki-67
results. 15 Recent series have suggested that
Ki-67 be considered as a continuous marker
rather than a set cut point. 16 These issues continue to impact the clinical utility of Ki-67 for
decision-making for adjuvant chemotherapy.
Ki-67 and the preoperative endocrine prognostic index (PEPI) score have been explored
in the neoadjuvant setting to separate postmenopausal women with endocrine-sensitive
versus intrinsically resistant disease and identify patients at risk for recurrent disease. 17
The on-treatment levels of Ki-67 in response
to endocrine therapy have been shown to be
more prognostic than baseline values, and
a decrease in Ki-67 as early as 2 weeks after
initiation of neoadjuvant endocrine therapy
is associated with endocrine-sensitive tumors
and improved outcome. The PEPI score was
developed through retrospective analysis of
the P024 trial18 to evaluate the relationship
between post-neoadjuvant endocrine ther-
apy tumor characteristics and risk for early
relapse. The score was subsequently validated
in an independent data set from the IMPACT
(Immediate Preoperative Anastrozole,
Tamoxifen, or Combined with Tamoxifen)
trial. 19 Patients with low pathological stage
(0 or 1) and a favorable biomarker profile
(PEPI score 0) at surgery had the best prog-
nosis in the absence of chemotherapy. On the
other hand, higher pathological stage at sur-
gery and a poor biomarker profile with loss
of ER positivity or persistently elevated Ki-67
(PEPI score of 3) identified de novo endo-
crine-resistant tumors that are higher risk for
early relapse. 20 The ongoing Alliance A011106
ALTERNATE trial (ALTernate approaches for
clinical stage II or III Estrogen Receptor posi-
tive breast cancer NeoAdjuvant TrEatment
in postmenopausal women, NCT01953588)
is a phase 3 study to prospectively test this
hypothesis.
21-Gene Recurrence Score (Oncotype DX Assay)
The 21-gene Oncotype DX assay is conducted
on paraffin-embedded tumor tissue and measures the expression of 16 cancer related
genes and 5 reference genes using quantitative polymerase chain reaction (PCR).
The genes included in this assay are mainly
related to proliferation (including Ki-67),
invasion, and HER2 or estrogen signaling. 21
Originally, the 21-gene recurrence score
assay was analyzed as a prognostic biomarker
tool in a prospective-retrospective biomarker
