Abstract PD01-02: Increased expression of phosporylated mTOR in metastatic breast tumors compared to primary tumors in patients who received adjuvant endocrine therapy

Abstract BACKGROUND: Activation of the PI3K pathway as an adaptive change in response to estrogen depletion results in acquired endocrine therapy resistance in vitro. Metastatic breast cancer patients with previous exposure to endocrine therapy do derive substantial benefit from the addition of an mTOR inhibitor to endocrine therapy compared to endocrine therapy alone. This suggests that compensatory PI3K pathway activation might play a role in the development of clinical resistance to endocrine therapy. We evaluated the activation of the downstream PI3K pathway protein mTOR in primary breast tumors and matched metastatic lesions. METHODS: From a previously described series of breast cancer patients from whom both primary tumor tissue as well as metastatic tumor tissue was collected, we selected estrogen receptor α (ERα) positive patients who had received endocrine therapy (N = 34) and who did not receive endocrine therapy (N = 37). The difference in expression of phosphorylated mTOR (p-mTOR) between primary and metastatic tumor was assessed by immunohistochemistry, which was scored by using the proportion of tumor cells with sub-membranous p-mTOR expression. We assessed whether this p-mTOR difference between primary and metastatic tumor was associated with clinico-pathological factors (location of metastasis, lymph node status, T-stage, grade, progesterone receptor status) or varied between patients who did and did not receive endocrine therapy, using Mann-Whitney tests. In addition we performed a linear regression model including the same clinico-pathological factors. RESULTS: In patients who had received endocrine therapy we observed an increase in p-mTOR expression in metastatic tumor lesions compared to the primary tumor (median difference 45%). This was significantly different from the mTOR changes observed in patients who did not receive endocrine therapy (median difference between metastatic and primary lesion 0 %) (p = 0.003). The difference remained significant in the multivariate regression model (p = 0.001). None of the other factors was significantly associated with a differential p-mTOR change. CONCLUSION: In patients who received previous adjuvant endocrine therapy, the increase in p-mTOR expression in metastatic tumor lesions compared to the primary tumor is significantly higher than in patients who did not receive endocrine therapy. Compensatory activation of the PI3K pathway might therefore be a clinically relevant resistance mechanism resulting in secondary endocrine therapy resistance. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr PD01-02.</jats:p

Abstract P6-05-08: Significant heterogeneity in ERalpha and PR receptor status in different distant breast cancer metastases of the same patient

Abstract Purpose: Receptor conversion for estrogen receptor alpha (ERα), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) in single distant breast cancer metastases has been described before. However, most patients develop multiple metastases. Heterogeneity in receptor status between different metastases of the same patient has not been studied, probably since such material is very rare. The consequence of such heterogeneity would mean that as many metastases as possible need to be biopsied to re-assess receptor status. We therefore aimed to study heterogeneity of receptor status between different distant metastases of the same patient in a relatively large group by re-staining all primary tumors and metastases with current optimal immunohistochemical methods on full sections. Material and methods: Formalin fixed paraffin embedded tissue of primary breast carcinomas and corresponding multiple (≥2) distant metastases from 38 female patients were collected from several pathology departments in The Netherlands and stained for ERα, PR and HER2 by IHC. We evaluated the heterogeneity of receptor status between the metastases and the correlation with the primary tumor. Results: In the 4 cases that showed ER conversion, 2 (50%) showed heterogeneity in receptor expression between different metastases of the same patient. Of the 17 cases that showed PR conversion, 12 cases (71%) showed heterogeneity in expression between metastases. There were no changes in the receptor profile of primary breast cancer to their metastases for HER2 in this group. Conclusion: In a significant number of metastatic breast cancer patients, there is heterogeneity in ER and PR receptor status between different breast cancer metastases of the same patient. This implies that as many metastases as possible need to be biopsied to re-assess receptor status and set the optimal indication for hormonal therapy in these patients. Alternatively, non-invasive assessment of the receptor status by molecular imaging may be an easier future way to assess receptor status of all metastatic lesions. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P6-05-08.</jats:p

Abstract P2-06-02: Genomic evolution from primary breast cancers to distant metastases

Abstract Purpose: Genomic evolution is an accepted concept during cancer development and progression. However, little is known about the changes that occur during the metastatic process despite the fact that breast cancer metastases are the leading cause of death in breast cancer patients. The purpose of this study was therefore to investigate whether distant breast cancer metastases show progression in copy number changes of onco- and tumor suppressor genes compared to their primary tumor. Material and methods: Multiplex ligation-dependent probe amplification (MLPA) was used to compare copy number of 21 established oncogenes and tumor suppressor genes between primary breast cancer samples and corresponding distant metastases in 55 patients. Genes studied were ESR1, EGFR, FGFR1, ADAM 9, IKBKB, PRDM14, MTDH, MYC, CCND1, EMSY, CDH1, TRAF4, CPD, MED1, HER2, CDC6, TOP2A, MAPT, BIRC5, CCNE1 and AURKA. Results: Overall, there was no significant difference in mean copy number between primary tumors (1.26 +/− 0.6) and metastases (1.27 +/− 0.64) (p = 0.826), but on the individual gene level, mean copy number for PRDM14 (p = 0,023), MED1 (p = 0.001) and CCNE1 (p = 0.039) were significantly higher while TRAF4 (p = 0.038) copy number was significantly lower in the metastases. Using dichotomized MLPA data, MTDH amplifications were significantly more frequent in the primary cancers compared to the metastases (27.3% vs.14.6%, p = 0.039), while significantly more CDH1 losses were found in the metastases compared to the primary tumor (23.6% vs. 9.1%, p = 0.039). Conclusion: Distant breast cancer metastases show genomic evolution from the primary cancer as reflected by copy number changes in several established onco- and tumor suppressor genes. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P2-06-02.</jats:p