Quantitative measurements of tumoral p95HER2 protein expression in metastatic breast cancer patients treated with trastuzumab: independent validation of the p95HER2 clinical cutoff

PURPOSE

P95HER2 (p95) is a truncated form of the HER2, which lacks the trastuzumab-binding site and contains a hyperactive kinase domain. Previously, an optimal clinical cutoff of p95 expression for progression-free survival (PFS) and overall survival (OS) was defined using a quantitative VeraTag assay (Monogram Biosciences) in a training set of trastuzumab-treated metastatic breast cancer (MBC) patients.

EXPERIMENTAL DESIGN

In the current study, the predictive value of the p95 VeraTag assay cutoff established in the training set was retrospectively validated for PFS and OS in an independent series of 240 trastuzumab-treated MBC patients from multiple institutions.

RESULTS

In the subset of 190 tumors assessed as HER2-total (H2T)-positive using the quantitative HERmark assay (Monogram Biosciences), p95 VeraTag values above the predefined cutoff correlated with shorter PFS (HR = 1.43; P = 0.039) and shorter OS (HR = 1.94; P = 0.0055) where both outcomes were stratified by hormone receptor status and tumor grade. High p95 expression correlated with shorter PFS (HR = 2.41; P = 0.0003) and OS (HR = 2.57; P = 0.0025) in the hormone receptor-positive subgroup of patients (N = 78), but not in the hormone receptor-negative group. In contrast with the quantitative p95 VeraTag measurements, p95 immunohistochemical expression using the same antibody was not significantly correlated with outcomes.

CONCLUSIONS

The consistency in the p95 VeraTag cutoff across different cohorts of patients with MBC treated with trastuzumab justifies additional studies using blinded analyses in larger series of patients.

Expression of estrogen receptor beta in the breast carcinoma of BRCA1 mutation carriers

BACKGROUND

Breast cancers (BC) in women carrying mutations in BRCA1 gene are more frequently estrogen receptor negative than the nonhereditary BC. Nevertheless, tamoxifen has been found to have a protective effect in preventing contralateral tumors in BRCA1 mutation carriers. The identification of the second human estrogen receptor, ERbeta, raised a question of its role in hereditary breast cancer. The aim of this study was to assess the frequency of ERalpha, ERbeta, PgR (progesterone receptor) and HER-2 expression in breast cancer patients with mutated BRCA1 gene and in the control group.

METHODS

The study group consisted of 48 women with BRCA1 gene mutations confirmed by multiplex PCR assay. The patients were tested for three most common mutations of BRCA1 affecting the Polish population (5382insC, C61G, 4153delA). Immunostaining for ERalpha, ERbeta and PgR (progesterone receptor) was performed using monoclonal antibodies against ERalpha, PgR (DakoCytomation), and polyclonal antibody against ERbeta (Chemicon). The EnVision detection system was applied. The study population comprised a control group of 120 BC operated successively during the years 1998-99.

RESULTS

The results of our investigation showed that BRCA1 mutation carriers were more likely to have ERalpha-negative breast cancer than those in the control group. Only 14.5% of BRCA1-related cancers were ERalpha-positive compared with 57.5% in the control group (P < 0.0001). On the contrary, the expression of ERbeta protein was observed in 42% of BRCA1-related tumors and in 55% of the control group. An interesting finding was that most hereditary cancers (75% of the whole group) were triple-negative: ERalpha(-)/PgR(-)/HER-2(-) but almost half of this group (44.4%) showed the expression of ERbeta.

CONCLUSION

In the case of BRCA1-associated tumors the expression of ERbeta was significantly higher than the expression of ERalpha. This may explain the effectiveness of tamoxifen in preventing contralateral breast cancer development in BRCA1 mutation carriers.