Improvement of the clinical applicability of the Genomic Grade Index through a qRT-PCR test performed on frozen and formalin-fixed paraffin-embedded tissues.
BACKGROUND
Proliferation and tumor differentiation captured by the genomic grade index (GGI) are important prognostic indicators in breast cancer (BC) especially for the estrogen receptor positive (ER+) disease. The aims of this study were to convert this microarray index to a qRT-PCR assay (PCR-GGI), which could be realized on formalin fixed paraffin embedded samples (FFPE), and to assess its prognostic performance and predictive value of clinical benefit in early and advanced ER+ BC patients treated with tamoxifen.


METHODS
The accuracy and concordance of the PCR-GGI with the GGI was assessed using BC patients for which frozen and FFPE tissues as well as microarray data were available (n = 19). The evaluation of the prognostic value of the PCR-GGI was assessed on FFPE material using a consecutive series of 212 systemically treated early BC patients. The predictive performance for tamoxifen benefit was assessed using two ER+ BC populations treated either with adjuvant tamoxifen only (n = 77+139) or first-line tamoxifen for advanced disease (n = 270).


RESULTS
The PCR-GGI is based on the expression of 8 genes (4 representative of the GGI and 4 reference genes). A significant correlation was observed between the microarray-derived GGI and the qRT-PCR assay using frozen (rho = 0.95, p < 10E-06) and FFPE material (rho = 0.89, p < 10E-06). The prognostic performance of the PCR-GGI was confirmed on FFPE samples (HRunivar. = 1.89; [95CI:1.01-3.54], p = 0.05). The PCR-GGI further identified two subgroups of patients with statistically different time to distant metastasis free survival (DMFS) across the two cohorts of ER+ BC patients treated with adjuvant tamoxifen. Additionally, the PCR-GGI was associated with response to tamoxifen in the advanced setting (HRunivar. = 1.98; [95CI:1.51-2.59], p = 6.9E-07).


CONCLUSIONS
PCR-GGI recapitulates in an accurate and reproducible manner the performances of the GGI using frozen and FFPE samples.
Toussaint
Jérôme
J
Translational Research Unit, Jules Bordet Institute, Brussels, Belgium. jerome.toussaint@bordet.be
Sieuwerts
Anieta M
AM
Haibe-Kains
Benjamin
B
Desmedt
Christine
C
Rouas
Ghizlane
G
Harris
Adrian L
AL
Larsimont
Denis
D
Piccart
Martine
M
Foekens
John A
JA
Durbecq
Virginie
V
Sotiriou
Christos
C
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000175:diagnosis / Q000188:drug therapy / Q000235:genetics*; D005260:Female; D005557:Formaldehyde; D005629:Frozen Sections; D052138:Genes, Neoplasm; D006801:Humans; D008875:Middle Aged; D020411:Oligonucleotide Array Sequence Analysis; D016612:Paraffin Embedding; D011237:Predictive Value of Tests; D011379:Prognosis; D012334:RNA, Neoplasm / Q000235:genetics; D011960:Receptors, Estrogen / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods*; D016019:Survival Analysis; D013629:Tamoxifen / Q000627:therapeutic use
D012334:RNA, Neoplasm; D011960:Receptors, Estrogen; D013629:Tamoxifen; D005557:Formaldehyde