The mammalian target of rapamycin pathway is widely activated without PTEN deletion in renal cell carcinoma metastases

BACKGROUND:

Inhibitors of the mammalian target of rapamycin (mTOR) are emerging as promising therapies for metastatic renal cell carcinoma (RCC). Because rational treatment strategies require understanding the activation status of the underlying signaling pathway being targeted at the desired stage of disease, the authors examined the activation status of different components of the mTOR pathway in RCC metastases and matched primary tumors.

METHODS:

The authors immunostained metastatic RCC samples from 132 patients and a subset of 25 matched primary RCCs with antibodies against phosphatidylinositol 3′‐kinase, PTEN, phospho‐Akt, phospho‐mTOR, and p70S6. PTEN genomic status was assessed by fluorescent in situ hybridization. Marker expression was correlated to clinicopathologic variables and to survival.

RESULTS:

The mTOR pathway showed widespread activation in RCC metastases of various sites with strong correlation between different components of this signaling cascade (P<.0001), but without significant PTEN genomic deletion. Only cytoplasmic phospho‐mTOR showed independent prognostic significance (P = .029) and fidelity between primary RCCs and their matched metastases (P = .004).

CONCLUSIONS:

Activation of various components of the mTOR signaling pathway in metastatic RCC lesions across various tumor histologies, nuclear grades, and metastatic sites suggests the potential for vertical blockade of multiple steps of this pathway. Patient selection may be improved by mTOR immunostaining of primary RCC. Cancer 2011. © 2010 American Cancer Society.     

Preliminary characterization of oral lesions associated with inhibitors of mammalian target of rapamycin in cancer patients

BACKGROUND:

Mammalian target of rapamycin (mTOR) inhibitors may have efficacy as an intervention for advanced malignancies. Oral ulceration (OU), reported as mucositis, has been a dose‐limiting toxicity for this new class of agents. An analysis of the appearance, course, and toxicity associations of mTOR inhibitor‐associated stomatitis (mIAS) demonstrated that the condition is distinct from conventional mucositis (CM) and more closely resembles aphthous stomatitis.

METHODS:

Safety data from 78 solid tumor patients enrolled in 2 Phase 1, multicenter trials of the mTOR inhibitor deforolimus (AP23573, MK‐8669) were evaluated. Adverse events (AEs) based on National Cancer Institute Common Toxicity Criteria for National Cancer Institute Common Terminology Criteria for Adverse Events (version 3.0) criteria were coded, consolidated, and stratified according to the presence or absence and duration of concordant OU. The relation between OU and other AEs was analyzed.

RESULTS:

Treatment‐emergent AEs were reported in 91% of 78 study participants. OUs were reported in 66%, appeared within 5 days of deforolimus administration, and were discrete, ovoid, superficial, well demarcated, and surrounded by an erythematous halo. Their clinical appearance and distribution were similar to that of aphthous stomatitis but inconsistent with CM. Patients with OU were more likely to have nonspecific rashes and acneiform dermatitis but not gastrointestinal AEs.

CONCLUSIONS:

OU associated with mTOR inhibitor therapy differed from CM. Lesions more closely resembled those of aphthous stomatitis. The lack of other gastrointestinal involvement but the presence of a higher incidence of concomitant cutaneous AEs provided additional evidence to suggest a distinction between mIAS and CM. Treatment strategies for aphthous stomatitis may be a rational approach for the prevention and control of mIAS. Cancer 2010. © 2010 American Cancer Society.     

Clinical and histopathologic characteristics of rash in cancer patients treated with mammalian target of rapamycin inhibitors

BACKGROUND:

Dermatologic adverse events stemming from anticancer therapies have become an increasingly frequent clinical problem. Inhibitors of mammalian target of rapamycin (mTOR), such as temsirolimus and everolimus, have been associated with a high rate of skin eruptions, but their clinical and histopathologic characteristics have not been explored.

METHODS:

A retrospective analysis of patients who were referred to the Dermatology Service for diagnosis and management of rash in the setting of therapy with the mTOR inhibitors everolimus and temsirolimus was performed. The parameters that were studied included the time to onset, clinical presentation at the time of dermatologic evaluation, associated symptoms, evolution, results of microbiologic studies, concomitant medications, the need for dose reduction and/or treatment interruption because of rash, and routine histopathology.

RESULTS:

In total, 13 patients were analyzed. Most rashes were mild (grade 1; 31%) and moderate (grade 2; 54%) in severity, and grade 3 rashes were observed only in 2 patients (15%). The trunk was the most frequently affected region (77%), with the scalp (23%), face (38%), neck (54%), and extremities (69%) also commonly involved. Erythematous papules and pustules constituted the predominant primary lesion morphology (62%). No unique or uniform histopathologic reaction pattern was observed. The most common reaction pattern was that of a mixed, spongiotic interface and perivascular dermatitis, which was observed in 7 of 11 patients (63%).

CONCLUSIONS:

Although mTOR inhibitors may commonly induce erythematous papules and pustules, they are associated with a spectrum of lesion morphologies and a variety of histopathologic findings. Further clinicohistologic correlation studies are needed. Cancer 2012. © 2012 American Cancer Society.     

Mammalian target of rapamycin is activated in human gastric cancer and serves as a target for therapy in an experimental model

The mammalian target of rapamycin (mTOR) has become an interesting target for cancer therapy through its influence on oncogenic signals, which involve phosphatidylinositol-3-kinase and hypoxia-inducible factor-1alpha (HIF-1alpha). Since mTOR is an upstream regulator of HIF-1alpha, a key mediator of gastric cancer growth and angiogenesis, we investigated mTOR activation in human gastric adenocarcinoma specimens and determined whether rapamycin could inhibit gastric cancer growth in mice. Expression of phospho-mTOR was assessed by immunohistochemical analyses of human tissues. For in vitro studies, human gastric cancer cell lines were used to determine S6K1, 4E-BP-1 and HIF-1alpha activation and cancer cell motility upon rapamycin treatment. Effects of rapamycin on tumor growth and angiogenesis in vivo were assessed in both a subcutaneous tumor model and in an experimental model with orthotopically grown tumors. Mice received either rapamycin (0.5 mg/kg/day or 1.5 mg/kg/day) or diluent per intra-peritoneal injections. In addition, antiangiogenic effects were monitored in vivo using a dorsal-skin-fold chamber model. Immunohistochemical analyses showed strong expression of phospho-mTOR in 60% of intestinal- and 64% of diffuse-type human gastric adenocarcinomas. In vitro, rapamycin-treatment effectively blocked S6K1, 4E-BP-1 and HIF-1alpha activation, and significantly impaired tumor cell migration. In vivo, rapamycin-treatment led to significant inhibition of subcutaneous tumor growth, decreased CD31-positive vessel area and reduced tumor cell proliferation. Similar significant results were obtained in an orthotopic model of gastric cancer. In the dorsal-skin-fold chamber model, rapamycin-treatment significantly inhibited tumor vascularization in vivo. In conclusion, mTOR is frequently activated in human gastric cancer and represents a promising new molecular target for therapy.     

Critical and diverse involvement of Akt/mammalian target of rapamycin signaling in human lung carcinomas

BACKGROUND: Aberrant signaling cascades emanating from epidermal growth factor receptor (EGFR) are involved in the complex network of oncogenic signaling in lung carcinomas. One representative cascade is the phosphatidylinositol 3‐kinase/Akt/mammalian target of rapamycin (mTOR) pathway. METHODS: The authors investigated the involvement of mTOR in the pathobiologic profiles of 150 specimens of lung carcinoma by immunohistochemistry and immunoblotting in correlation with the upstream and downstream proteins Akt and p70S6‐kinase (S6K), respectively. RESULTS: Immunohistochemistry revealed Akt activation in 44% of tumors and mTOR expression in 68.7% of tumors, and the preponderance of activation was observed in adenocarcinoma (AC) (100%). Phosphorylated mTOR (p‐mTOR) was observed in 53.3% of tumors and had the highest frequency in AC (89.7%). In AC, the frequency of p‐mTOR staining was higher in the well differentiated subtype, in particular, in the acinar structure. However, little correlation was observed between the activation of mTOR and Akt, except in the 5 AC specimens that harbored an EGFR gene mutation, which exhibited constitutive activation of both Akt and mTOR. Conversely, in squamous cell carcinomas, mTOR activation was associated with a significantly higher frequency of lymph node metastasis. CONCLUSIONS: The results of this study suggested the dual functions of mTOR. First, mTOR may function not only in the proliferation of tumor cells as an effector molecule downstream of EGFR but also possibly in the morphogenesis of AC. Second, the activation of mTOR may play a key role in metastasis in squamous cell carcinoma. Overall, the current results demonstrated the potential for the application of rapamycin, an mTOR inhibitor, as an additional novel component of chemotherapy for a defined subset of patients with lung carcinoma. Cancer 2009. © 2008 American Cancer Society.     

Targeted inhibition of mammalian target of rapamycin for the treatment of advanced renal cell carcinoma

Clinical trials have validated the importance of mammalian target of rapamycin (mTOR) as a targeted mechanism in the treatment of renal cell carcinoma (RCC). Temsirolimus, an mTOR inhibitor that is approved for treatment of advanced RCC, has demonstrated both overall survival benefits and progression‐free survival benefits versus interferon?α as first‐line treatment for patients with poor prognostic features. Exploratory subset analyses indicated that temsirolimus benefits patients with RCC regardless of tumor histology or nephrectomy status. Everolimus, the second mTOR inhibitor to demonstrate activity in RCC, improved progression‐free survival versus placebo in patients whose disease progressed after treatment with vascular endothelial growth factor receptor tyrosine kinase inhibitors (sunitinib, sorafenib, or both); benefit was observed for all risk groups. Deforolimus also exhibited antitumor activity against RCC in early clinical studies. There is now compelling clinical evidence for the effectiveness of targeting mTOR in the treatment of RCC. Cancer 2009. © 2009 American Cancer Society.     

Age-related somatic mutations in the cancer genome

Aging is associated with an increased risk of cancer, possibly in part because of an age-related increase in mutations in normal tissues. Due to their extremely low abundance, somatic mutations in normal tissues frequently escape detection. Tumors, as clonal expansions of single cells, can provide information about the somatic mutations present in these cells prior to tumorigenesis.Here, we used data from The Cancer Genome Atlas (TCGA), to systematically study the frequency and spectrum of somatic mutations in a total of 6,969 patients and 34 different tumor types as a function of the age of the patient. After using linear modeling to control for the age structure of different tumor types, we found that the number of identified somatic mutations increases exponentially with age. Using additional data from the literature, we found that accumulation of somatic mutations is associated with cell division rate, cancer risk and cigarette smoking, with the latter also associated with a distinct spectrum of mutations.Our results confirm that aging is associated with the accumulation of somatic mutations, and strongly suggest that the level of genome instability of normal cells, modified by both endogenous and environmental factors, is the main risk factor for cancer.     

哺乳动物雷帕霉素靶蛋白在胃癌的研究进展

 哺乳动物雷帕霉素靶蛋白(mTOR)在调节细胞增殖、生长、能量代谢等方面起重要作用,在很多肿瘤中表达过量,通过mTOR抑制剂雷帕霉素等可以起到抑制胃癌发展的作用。联合mTOR上下游通路研究对胃癌的早期诊断、监测疗效及预后价值更大。     

New developments in mammalian target of rapamycin inhibitors for the treatment of sarcoma

Although sarcomas account for a small portion of solid malignancies, currently, there are few treatment options for sarcomas, particularly for advanced disease. The mammalian target of rapamycin (mTOR), a serine-threonine protein kinase in the phosphatidylinositol 3-kinase/serine/threonine protein kinase Akt signaling pathway, has an important role in the regulation of protein synthesis, cell proliferation, angiogenesis, and metabolism. Alterations of the mTOR signaling pathway are common in malignancies, including several types of sarcoma. Therefore, mTOR is a potentially important therapeutic target in these diseases. Rapamycin and its analogs (rapalogs) are effective anticancer agents in a broad range of preclinical models. Clinical trials with these agents alone and in combination with other anticancer agents, including chemotherapy and targeted therapies, have demonstrated potential clinical benefit in several types of sarcoma. The evidence from both preclinical and clinical studies supports further study of mTOR-targeting rapalogs in the treatment of various subtypes of sarcoma.     

Role of mammalian target of rapamycin complex 2 in primary and secondary liver cancer

The mammalian target of rapamycin (mTOR) acts in two structurally and functionally distinct protein complexes, mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2). Upon deregulation, activated mTOR signaling is associated with multiple processes involved in tumor growth and metastasis. Compared with mTORC1, much less is known about mTORC2 in cancer, mainly because of the unavailability of a selective inhibitor. However, existing data suggest that mTORC2 with its two distinct subunits Rictor and mSin1 might play a more important role than assumed so far. It is one of the key effectors of the PI3K/AKT/mTOR pathway and stimulates cell growth, cell survival, metabolism, and cytoskeletal organization. It is not only implicated in tumor progression, metastasis, and the tumor microenvironment but also in resistance to therapy. Rictor, the central subunit of mTORC2, was found to be upregulated in different kinds of cancers and is associated with advanced tumor stages and a bad prognosis. Moreover, AKT, the main downstream regulator of mTORC2/Rictor, is one of the most highly activated proteins in cancer. Primary and secondary liver cancer are major problems for current cancer therapy due to the lack of specific medical treatment, emphasizing the need for further therapeutic options. This review, therefore, summarizes the role of mTORC2/Rictor in cancer, with special focus on primary liver cancer but also on liver metastases.     

Mechanisms of mammalian target of rapamycin inhibition in sarcoma: present and future

The mammalian target of rapamycin (mTOR) is a protein kinase that plays a pivotal role in the control of cell growth and development. A part of the PI3K/Akt pathway, mTOR responds to growth factor stimuli as well as nutrient availability by variations in downstream phosphorylation. Increasing knowledge of the upstream regulators and downstream targets of mTOR has led to the development of anticancer drugs that suppress protein synthesis and metabolism. Rapamycin (sirolimus) and three rapamycin analogues are currently being evaluated in clinical trials: temsirolimus (CCI-779, Wyeth), everolimus (RAD001, Novartis Pharma AG), and AP23573 (Ariad Pharmaceuticals Inc.). This review will highlight the role of these inhibitors in the treatment of sarcoma.     

Activation of mammalian target of rapamycin pathway confers adverse outcome in nonsmall cell lung carcinoma

BACKGROUND:

Dysregulation of the mammalian target of rapamycin (mTOR) pathway has been shown to contribute to tumorigenesis. This study explored protein expression profiles of mTOR pathway and the relationship with prognosis in patients with nonsmall cell lung carcinoma (NSCLC).

METHODS:

The protein expression profiles of mTOR/phosphorylated (p‐)mTOR, phosphoinositide‐dependent kinase 1 (PDK1)/p‐PDK1, p‐Akt1, and P70 ribosomal protein S6 kinase (P70S6K)/p‐P70S6K were determined via immunohistochemical staining assay. The clinical prognostic values of both single and combined protein expression were investigated with univariate and multivariate survival analysis.

RESULTS:

Compared with normal lung tissues, the protein levels of mTOR/p‐mTOR, p‐Akt1 Ser473/Thr308, and P70S6K/p‐P70S6K were higher (all P < .05), whereas p‐PDK1 was lower (P < .05) in tumor tissues. p‐mTOR expression was associated with histological differentiation, histological type, lymph node invasion, and stage (all P < .05). Overall survival in NSCLC patients was significantly shorter in cases with positive phenotype for p‐mTOR, p‐PDK1, and p‐P70S6K (all P < .05). Subjects with coexpression of any 2 of p‐mTOR, p‐PDK1, p‐Akt1 Ser473, and p‐P70S6K demonstrated worse prognosis than those expressing no biomarker or any 1 biomarker alone (all P < .05). Multivariate analysis showed that the combination of p‐mTOR/p‐P70S6K is an independent prognostic factor in addition to tumor stage.

CONCLUSIONS:

This study provides clinical evidence that activated components of mTOR pathway, not total protein, are predictors of poor prognosis in NSCLC. Moreover, evaluating protein‐expression profiles of these molecules might be a new strategy for individual therapy in subjects with NSCLC. Cancer 2011;. © 2011 American Cancer Society.     

Modulation of the activities of AMP-activated protein kinase, protein kinase B, and mammalian target of rapamycin by limiting energy availability with 2-deoxyglucose

2-Deoxyglucose (2-DG), which has been shown to inhibit mammary carcinogenesis, was used as a metabolic probe to investigate effects of limiting energy availability (reduced cellular ATP) on patterns of proteins' phosphorylation that play a role in the development of cancer. Experiments were conducted using a human breast cancer cell line, MDA-MB-468, and 1-methyl-1-nitrosourea-induced rat model for mammary carcinogenesis. Under in vitro conditions in which cellular ATP concentration decreased rapidly with increasing 2-DG in a dose and time dependent manner, levels of phosphorylated mammalian target of rapamycin (P-mTOR) decreased in parallel to decreases in ATP concentration. Concomitantly, phosphorylation of two upstream regulators of mTOR, AMP-activated protein kinase (AMPK) and Akt/protein kinase B were increased and decreased, respectively, with increased levels of phosphorylated acetyl-CoA carboxylase as an indicator of AMPK activation. Levels of insulin like growth factor 1-receptor and phosphoinositide-3 kinase p110 alpha were also reduced. Similar effects were observed in mammary carcinomas in vivo at concentration of 0.03% (w/w) dietary 2-DG that inhibited carcinogenesis. In vitro, downregulation of mTOR was accompanied by decreases in phosphorylation of two of mTOR's targets, 70-kDa ribosomal protein S6 kinase and eukaryote initiation factor 4E binding protein 1. Glucose treatment reversed 2-DG effects. When cells were transfected with dominant-negative AMPK alpha 2, effects of 2-DG on mTOR and its downstream effectors were diminished, providing evidence of a link between AMPK and mTOR when energy availability was limited. This work indicates that AMPK, Akt, and mTOR are candidate targets for efforts to inhibit the carcinogenic process by limiting energy availability.     

Synergistic effect of rapamycin and cisplatin in endometrial cancer cells

BACKGROUND:

Mammalian target of rapamycin (mTOR) inhibitors modulate signaling pathways involved in cell cycle progression, and phase 2 trials for endometrial cancer are currently being conducted. Because rapamycin is known to enhance the cytotoxicity of chemotherapeutic drugs, the authors' goal was to examine the effects of rapamycin and cisplatin in endometrial cancer cell lines.

METHODS:

By using Ishikawa and ECC‐1 cells, cell proliferation was assessed after exposure to rapamycin, cisplatin, or both in combination. The combination index (CI) was calculated using the method of Chou and Talalay. Apoptosis was evaluated by flow cytometry. Immunoblot analysis was performed to assess expression of S6 kinase 1 and the DNA mismatch repair proteins, MSH2 and MSH6. mTOR small interfering (siRNA) was transfected into the cell lines, and proliferation and apoptosis were assessed after exposure to cisplatin.

RESULTS:

Cisplatin inhibited growth in a dose‐dependent manner in both cell lines (median inhibition concentration of 8‐13 μM). Simultaneous exposure of cisplatin in combination with rapamycin resulted in a significant synergistic antiproliferative effect (CI < 1). Rapamycin increased cisplatin‐induced apoptosis and stimulated expression of MSH2 and MSH6 in the cisplatin‐treated cell lines. Cell growth was significantly decreased in cells transfected with mTOR siRNA and treated with cisplatin compared with either alone (CI < 1). Transfection of mTOR siRNA did not induce apoptosis, but combined treatment with cisplatin increased apoptosis over that of cisplatin alone.

CONCLUSIONS:

The results of the current study provide evidence of a synergistic relation between rapamycin and cisplatin in both inhibition of cell growth and induction of apoptosis. This suggests that rapamycin and cisplatin may be a rational combination of a targeted therapy for endometrial cancer. Cancer 2009. © 2009 American Cancer Society.     

哺乳动物雷帕霉素靶蛋白的反馈激活机制在肿瘤中的研究进展

哺乳动物雷帕霉素靶蛋白（mTOR）作为生长因子和氨基酸特别是亮氨酸所激发的信号通路的汇合点,在肿瘤细胞中起中心调控作用.近些年,人们逐渐认识到mTOR的反馈激活机制是影响雷帕霉素及其类似物抗肿瘤疗效的重要因素之一.因此,针对mTOR的反馈激活机制及联合应用相关抑制剂协同阻断这一机制的研究成为肿瘤防治的新热点.     

Neuroendocrine tumors resistant to mammalian target of rapamycin inhibitors: A difficult conversion from biology to the clinic

Deregulation of the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) - mammalian target of rapamycin (mTOR) signaling pathway is one of the most commonly-involved pathways in tumorigenesis. It has also been reported as altered in neuroendocrine tumors (NETs). mTOR inhibitors used in clinical practice are derived from rapamycin, an anti-cancer agent also used as an immunosuppressor after organ transplantation. Everolimus and temsirolimus are the two rapamycin-derived mTOR inhibitors used in NETs. Notably everolimus has been approved in advanced progressive well/moderately-differentiated pancreatic NETs (pNETs). It inhibits specifically the mTORC1 subunit of mTOR, not interacting with mTORC2. Although everolimus produced a significant prolongation of progression-free survival a number of patients with pNETs do not benefit from the drug due to early or late progression. Two supposed mechanisms of resistance to mTOR inhibitors are Akt and PI3K activation, by means of mTORC2 and insulin growth factor (IGF) - IGF receptor signaling, respectively. BEZ235 is a multi-targeted inhibitor binding to PI3K, mTORC1 and mTORC2, therefore potentially turning off all the supposed molecular targets of resistance to everolimus. The two clinical trials designed in pNETs were stopped early due to unmet statistical endpoint and the global clinical development of BEZ235 was also halted. Tolerability of this drug was challenging and conditioned the feasibility of therapy. The BEZ experience is an example of the huge difference between the preclinical and clinical setting and prompts us to pay more attention to the phase I step of clinical development and the design of phase II clinical trials.     

NV‐128, a novel isoflavone derivative,induces caspase‐independent cell death through the Akt/mammalian target of rapamycin pathway

BACKGROUND:

Resistance to apoptosis is 1 of the key events that confer chemoresistance and is mediated by the overexpression of antiapoptotic proteins, which inhibit caspase activation. The objective of this study was to evaluate whether the activation of an alternative, caspase‐independent cell death pathway could promote death in chemoresistant ovarian cancer cells. The authors report the characterization of NV‐128 as an inducer of cell death through a caspase‐independent pathway.

METHODS:

Primary cultures of epithelial ovarian cancer (EOC) cells were treated with increasing concentration of NV‐128, and the concentration that caused 50% growth inhibition (GI₅₀) was determined using a proprietary assay. Apoptotic proteins were characterized by Western blot analyses, assays that measured caspase activity, immunohistochemistry, and flow cytometry. Protein‐protein interactions were determined using immunoprecipitation. In vivo activity was measured in a xenograft mice model.

RESULTS:

NV‐128 was able to induce significant cell death in both paclitaxel‐resistant and carboplatin‐resistant EOC cells with a GI₅₀ between 1 μg/mL and 5 μg/mL. Cell death was characterized by chromatin condensation but was caspase‐independent. The activated pathway involved the down‐regulation of phosphorylated AKT, phosphorylated mammalian target of rapamycin (mTOR), and phosphorylated ribosomal p70 S6 kinase, and the mitochondrial translocation of beclin‐1 followed by nuclear translocation of endonuclease G.

CONCLUSIONS:

The authors characterized a novel compound, NV‐128, which inhibits mTOR and promotes caspase‐independent cell death. The current results indicated that inhibition of mTOR may represent a relevant pathway for the induction of cell death in cells resistant to the classic caspase‐dependent apoptosis. These findings demonstrate the possibility of using therapeutic drugs, such as NV‐128, which may have beneficial effects in patients with chemoresistant ovarian cancer. Cancer 2009. © 2009 American Cancer Society.     

Comparison of Akt/mTOR signaling in primary breast tumors and matched distant metastases

BACKGROUND.

The Akt/mammalian target of the rapamycin (mTOR) signaling pathway represents a promising target for cancer therapy. The phosphorylation status of Akt and of mTOR's phosphorylation target eukaryotic initiation factor 4E‐binding protein 1 (4E‐BP1) is often used to assess the activity of Akt and mTOR signaling. The purpose of this study was to determine whether primary tumors differ from their metastasis in their expression of pAkt and p4E‐BP1.

METHODS.

Primary breast tumors and their distant metastases surgically resected from the same patients were evaluated with immunohistochemical analysis (IHC) for pAkt (Ser473) and p4E‐BP1 (Ser65). The agreement between the IHC results for the primary tumor and metastases was evaluated with Cohen kappa (κ).

RESULTS.

Most primary breast tumors and metastatic tumors expressed pAkt (76% of each). Of the 23 matched evaluable pairs, however, 11 (47.8%) had discordant IHC results (κ ?0.31; 95% confidence interval [CI], ?0.49 to ?0.13). Similarly, although most of the primary and metastatic tumors were positive for p4E‐BP1 (75% and 74%), of the 23 matched evaluable pairs, 8 (47.8%) were discordant (κ 0.10; 95% CI, ?0.33–0.52).

CONCLUSIONS.

In this series, most primary breast tumors and metastases expressed pAkt and p4E‐BP1 by IHC. Concordance between IHC findings in primary tumors and metastases was poor, however. Further work is needed to determine whether this reflects true biological heterogeneity or poor reproducibility of IHC with phosphospecific antibodies, and to identify which biomarkers can be assessed most reproducibly in primary tumors to predict activity of Akt/mTOR signaling and sensitivity to pathway inhibitors. Cancer 2008. ©2008 American Cancer Society.