Breast Cancer Subtypes Identified by the ER , PR and HER-2 Status in Thai Women

Breast cancer is the most common cancer in women worldwide. Etiology of breast cancer is unclear, but is linked with various genetic abnormalities. Data from research studying on gene microarrays suggested that each breast cancer may have different genetic profiles. Based on genetic profiles, invasive ductal carcinoma (IDC) is classified into different 5 molecular subtypes: luminal-A, luminal-B, HER-2, basal and normal-breast like subtypes (Sorlie et al., 2001;Sorlie et al., 2003). Different subtypes may have different presenting features, different locoregional relapse, and different prognosis (Ihemelandu et al., 2008;Nguyen et al., 2008;Voduc et al., 2010;Wiechmann et al., 2009). Basal-like and HER2 subtypes were associated with aggressive clinical behaviors and poor survival outcome. While, patient with luminal A subtype had the best survival outcome (Carey et al., 2006;Kyndi et al., 2008). Gene expression profiling by DNA microarray is


Introduction
Breast cancer is the most common cancer in women worldwide.Etiology of breast cancer is unclear, but is linked with various genetic abnormalities.Data from research studying on gene microarrays suggested that each breast cancer may have different genetic profiles.Based on genetic profiles, invasive ductal carcinoma (IDC) is classified into different 5 molecular subtypes: luminal-A, luminal-B, HER-2, basal and normal-breast like subtypes (Sorlie et al., 2001;Sorlie et al., 2003).Different subtypes may have different presenting features, different locoregional relapse, and different prognosis (Ihemelandu et al., 2008;Nguyen et al., 2008;Voduc et al., 2010;Wiechmann et al., 2009).Basal-like and HER-2 subtypes were associated with aggressive clinical behaviors and poor survival outcome.While, patient with luminal A subtype had the best survival outcome (Carey et al., 2006;Kyndi et al., 2008).
Gene expression profiling by DNA microarray is expensive and may not be feasible in clinical practice.The technology requires a special platform and expertise.In general clinical practice, expression of estrogen receptor (ER), progesterone receptor (PR) and HER-2 are used to identify aggressiveness of breast cancer, and thus tailoring the treatment.Although, ER, PR and HER-2 status may not accurately classify the subtypes, the three markers has been used as surrogate markers to identify various breast cancer subtypes (Nguyen et al., 2008;Wiechmann et al., 2009).Moreover, the technique of immunohistochemistry in identifying expression of ER, PR and HER-2 is much easier and cheaper than gene microarray, but provides significant information to discriminate good and poor prognosis breast cancer.
Therefore, this study aimed primarily to document subtypes of breast cancer, identified by ER, PR and HER-2 status in Thai women.In addition, attention was focused on relationships between the various breast cancer subtypes and a number of important clinico-pathological features.

Materials and Methods
A total of 321 patients with 324 primary invasive ductal carcinoma (including 3 patients with bilateral breast cancer) diagnosed and had clinical and pathological information available at Department of Surgery, Faculty of Medicine Siriraj Hospital during November 2009 to June 2010 were included in the study.Bilateral breast cancers were regarded individually on the basis of the characteristics of each cancer.The study was ethically approved by the Institutional Board Review.
Percentage was used in calculation of most demographic and some clinical data.When comparing the clinicopatholocial characteristics amongst different subtypes, Chi-square (X 2 ) test was used for binary variables and analysis of variance (ANOVA) was used for continuous variables .Multivariate logistic regression was used to determine whether subtype was independently predictive of nodal involvement and/or multicentric/multifocal disease after controlling for age, tumor size, and tumor grade (high vs. intermediate/low).Luminal-A was the reference group.Patients with missing data were excluded from multivariate analysis.All statistical tests were two sided.P-value of ≤ 0.05 was considered statistical significant.All statistical analyses were performed by SPSS version 12 (SPSS,Chicago,IL).
On multivariate analysis, subtypes were not predictive  (Wiechmann et al., 2009), whereas the figure was 13% in this study in Thai women.HER-2 subtype possibly resulted in a poor outcome with a high locoregional relapse after breast conserving surgery and mastectomy (Kyndi et al., 2008;Nguyen et al., 2008).Therefore, this might highlight the difference in breast cancer between Asian and Western women, in term of tumor aggressiveness.However, in this study, not all patients who had HER-2 2+ on immunohistochemistry were confirmed with standard FISH or CISH techniques.
Moreover, findings in the study have confirmed the aggressiveness of HER-2 subtype breast cancer, as previously evidenced (Sorlie et al., 2001;Sotiriou et al., 2003).Patients with HER-2 subtypes in this study were likely to have multicentricity/multifocality, as well as large tumors.In addition, on multivariated analysis, high number of N2 and N3 diseases (nodal involvement ≥ 4) and high percentage of grade 3 were documented in HER-2 subtype tumor.
Triple negative (ER, PR and HER-2 negative) breast cancer is linked with a poor clinical outcome (Hudis and Gianni, 2011), and is approximately comparable to basal-like subtype on gene microarray.In our study from Thai women, basal-like subtype breast cancer or triple negative comprised 15%, which was equivalent to the study in a study from the USA (Wiechmann et al., 2009).Based on findings in our study, 28% of breast cancer women were either basal-like or HER-2 subtype, comparing with 20% in the Western women.This, again, may explain more aggressiveness and poorer clinical outcome of breast cancer in the Thai women and possibly other Asian women.
However, this study had some limitations were addressed here.Firstly, expression of ER, PR and HER-2 was used in order to determine subtype.In fact, although it is more feasible, it may not be accurately comparable to subtypes identified by gene microarray.The use of additional markers, such as Ki-67, is suggested in the further study.Secondly, identification of HER-2 positivity was mainly based on immunohistochemistry.Only 5 of 55 with HER-2 2+ were tested with FISH or CISH (all were negative).These may conceivably lead to potential misclassification of a subset of luminal-B tumors into the luminal-A subtype and a subset of HER-2 tumors into the basal-like subtype.
In conclusion, most invasive ductal carcinomas in Thai women were luminal-A subtype.Percentages of HER-2 and hasal-like tumors were higher, as compared with a recent study from the USA.HER-2 subtype seemed to relate with poor pathological features.Tumor size, tumor grade and ALI were related with nodal involvement.Tumor size and ALI were related with high volume nodal involvement.

Discussion
Advance in basic breast cancer research, in particular DNA microarray technology, has resulted in a new classification of breast cancer subtypes.The breast cancer subtypes related to various clinical outcomes, including overall survival (Ihemelandu et al., 2008;Sorlie et al., 2001).Luminal subtypes demonstrated better clinical outcomes than basal like and HER-2 subtypes (Sorlie et al., 2001;Sotiriou et al., 2003).
Evidence suggested that subtypes of breast cancer identified by DNA microarray may approximately relate to expression of commonly used markers in breast cancers: ER, PR and HER-2 status (Nguyen et al., 2008;Wiechmann et al., 2009), and use of three markers is easier and more cost-effectiveness in clinic, comparing with DNA microarray.In a recent consensus at St. Gallen in 2011, additional immunohistochemical staining of Ki-67 was supported for defining tumor subtypes, mainly in the distinction between luminal A and luminal B subtypes (Goldhirsch et al., 2011).
In this study, expression of ER PR and HER-2 are used to classify breast cancer into various subtypes.The findings from the study demonstrated different information, in the Asian population, where expression of markers may be different from information reported from the Western population.More frequent HER-2 subtype was observed in Thai women.In a study from the USA, HER-2 subtype comprised 6% of all invasive ductal cancer