Results

*Acknowledgement: We are grateful to the ABC Trial Working and Biological Studies Groups, the ATAC Trialists and Cancer Research UK for funding.

ER and HER2 expression are POSITIVELY correlated in HER2 non-over expressing breast cancer Pinhel I, Hills M, Drury S, Salter J, Johnson L, Barrett-Lee P, Harris A, Dowsett M on behalf of the NCRI Adjuvant Breast Cancer Trialists*; Institute of Cancer Research

and Royal Marsden Hospital, London, United Kingdom; Velindre NHS Trust, Cardiff, United Kingdom; John Radcliffe Hospital, Oxford, United Kingdom.

The expected negative correlation between levels of ER and HER2 expression was found in HER2 +ve tumours (r=-0.45, p=0.0028) (Figure 3). In contrast in HER2-ve tumours (ER+ve and ER-ve combined) there was a significant POSITIVE correlation between ER and HER2 mRNA levels (r=0.43, p<0.0001). As a result in HER2ve tumours the quantitative level of HER2 was higher in ER+ve than ERve tumours (mean fold difference 1.74, p<0.0001). There was a mean 5.8-fold higher HER2 transcript levels in HER2+ve vs HER2ve tumours in ER+ve disease and 12.9-fold higher in ERve disease.

The expected negative correlation between levels of ER and HER2 expression was found in HER2 +ve tumours (r=-0.45, p=0.0028) (Figure 3). In contrast in HER2-ve tumours (ER+ve and ER-ve combined) there was a significant POSITIVE correlation between ER and HER2 mRNA levels (r=0.43, p<0.0001). As a result in HER2ve tumours the quantitative level of HER2 was higher in ER+ve than ERve tumours (mean fold difference 1.74, p<0.0001). There was a mean 5.8-fold higher HER2 transcript levels in HER2+ve vs HER2ve tumours in ER+ve disease and 12.9-fold higher in ERve disease.

Matched results were available from all analyses for 257 ABC patients. ER was +ve in 67% of cases. HER2 distribution by IHC and FISH is represented in Table 1. For HER2, a significant difference between the four IHC categories was observed at the mRNA level (Figure 1).

The positive correlation though weaker was maintained in the ER+ve HER2ve group (r=0.24, p=0.0023) and was present to a similar extent in that subgroup in TransATAC (r=0.25, p<0.00001). The positive association was also significant in ER IHC analyses in ABC: mean±95%CI H-scores were 90±19 and 134±19 in the 0 and 1+ HER2 IHC categories, respectively (p=0.0013) (Figure 4).

HER2FISH

Negative Positive Not available Total

IHC

0 86 1 9 96

1+ 91 2 8 101

2+ 13 2 4 19

3+ 5 29 3 37

Not Available

4 - - 4

Total 199 34 24 257

Table 1. HER2 distribution by IHC and FISH.

ER and HER2 expression are positively correlated at both protein and transcript levels in HER2ve breast cancer in contrast to their negative correlation in HER2+ve disease. The distinction between HER2+ve and HER2ve is greater in ERve than ER+ve disease and this may lead to greater diagnostic uncertainties in ER+ve patients. These findings may also have importance for signaling pathways and application of targeted therapy in HER2ve disease.

DiscussionDiscussion

ConclusionsConclusions

ReferencesReferences1.Konecny et al, JNCI 2003, 95: 142-53.2.ABC Trialists, JNCI 2007, 99: 506-15.3.Dowsett et al, Cancer Res 2009, 69suppl: 75s.4.Paik et al, NEJM 2008, 358(13): 1409-11.

HER2 mRNA level overlaps in tumours conventionally considered negative (IHC 0, 1+, 2+ FISH-ve) and positive (IHC 2+ FISH+ve or 3+). Similar data has been published by Paik et al (4) and its biological significance is uncertain at present.It is notable that IHC 1+ category shows higher mRNA levels than the 0 category suggesting more biological meaning to the separation of these 2 groups based on IHC staining and this is supported by the positive correlation which we observe between ER and HER2 expression by IHC (Figure 4).

ER and HER2 levels were assessed by IHC (6F11 antibody and HercepTest, respectively) on tissue microarrays and q-RT-PCR in formalin-fixed primary breast cancers from 429 patients in the tamoxifen arm of the ABC Trial (2). ER by IHC was H-scored.

HER2 amplification status was assessed with the PathVysion 2-probe FISH test.

Transcript levels for ER and HER2 from 1139 HER2ve TransATAC tumours were available from the Oncotype DX test (3).

ER and HER2 are the most commonly measured biomarkers in breast cancer and are important targets for therapy.

ER and HER2 positivity are known to be inversely correlated and among ER positive (+ve) tumours, ER expression is higher in HER2 non-overexpressing (ve) than HER2 overexpressing (+ve) disease (1).

However, very few studies have evaluated the quantitative relationship between ER and HER2 expression in HER2ve tumours.

Here, the expression of ER and HER2 were measured at both the mRNA and protein level in HER2 +ve and ve breast carcinomas.

AimAim

Material & MethodsMaterial & Methods

BackgroundBackground

To determine the relationship between ER and HER2 expression according to HER2 amplification status.

ER mRNA levels were significantly higher in IHC categories 0, 1+ and 2+ than in IHC 3+ FISH+ve samples (Mann-Whitney, Figure 2).

Figure 3. Correlation of ER and HER2 expression. HER2 -ve, HER2 FISH -ve and IHC 0/1+/2+, n=214. HER2 +ve, HER2 FISH +ve and/or IHC 3+, n=42.

Figure 1. HER2 mRNA expression according to IHC categories. Mean with 95%CI.

Figure 2. ER mRNA expression according to HER2 protein expression and gene amplification. Mean with 95%CI (IHC2+FISH-ve 95%CI: -5.1 to 5.8).

p<0.0001

p=0.0025

p=0.007

p=0.0114

p<0.0001

p=0.0095

Figure 4. ER protein expression according to HER2 protein expression and gene amplification. Mean with 95%CI (IHC2+FISH-ve 95%CI: -892.2 to 1045).