Different ODE models of tumor growth can deliver similar results.

BACKGROUND: Simeoni and colleagues introduced a compartmental model for tumor growth that has proved quite successful in modeling experimental therapeutic regimens in oncology. The model is based on a system of ordinary differential equations (ODEs), and accommodates a lag in therapeutic action through delay compartments. There is some ambiguity in the appropriate number of delay compartments, which we examine in this note. METHODS: We devised an explicit delay differential equation model that reflects the main features of the Simeoni ODE model. We evaluated the original Simeoni model and this adaptation with a sample data set of mammary tumor growth in the FVB/N-Tg(MMTVneu)202Mul/J mouse model. RESULTS: The experimental data evinced tumor growth heterogeneity and inter-individual diversity in response, which could be accommodated statistically through mixed models. We found little difference in goodness of fit between the original Simeoni model and the delay differential equation model relative to the sample data set. CONCLUSIONS: One should exercise caution if asserting a particular mathematical model uniquely characterizes tumor growth curve data. The Simeoni ODE model of tumor growth is not unique in that alternative models can provide equivalent representations of tumor growth.

Known Knowns, Known Unknowns, and Unknown Unknowns: Coverage in MS Experiments.

A mathematical model from ecology, namely, the capture-recapture model with a closed population and time-varying and heterogeneous individual probabilities of capture, is implemented to model the number of protein identifications across the various cycles of a mass spectroscopy experiment. Rcapture, a package available in the R computing environment, can easily provide estimates of the cardinality of the proteome from such experiments. Alternatively, model fitting can be undertaken in other software platforms, such as Matlab, that can accommodate general linear models. It has not escaped our notice that capture-recapture models can be more broadly applied to other settings, so as to estimate the number of missing observations in an experiment.

Early detection of hepatocellular carcinoma using autoantibody profiles from a panel of tumor-associated antigens.

BACKGROUND: Multiple antigen miniarrays used for detecting autoantibodies to tumor-associated antigens (TAAs) can be a useful approach for cancer detection and diagnosis. We here address a very specific question: might there be autoimmune responses to TAAs which precede clinical detection of hepatocellular carcinoma (HCC) in HBV and HCV chronic liver disease patients under continuous medical surveillance, and if so, could these anti-TAAs be added to the armamentarium of diagnostic tests? METHODS: We here examine the utility of a panel of 12 TAAs for the diagnosis of hepatocellular carcinoma (HCC). We derived a predictive rule for the presence of HCC based on the panel, from a cohort comprising 160 HCC patients and 90 normals. We then applied this rule to sequential anti-TAA data from a cohort of 17 HCC patients, from whom this information was available prior to diagnosis. RESULTS: The predictors (autoantibodies to HCC1, P16, P53, P90, and survivin) indicated the presence of HCC prior to diagnosis in 16 of the 17 patients, at a median lead time of 0.75 year. CONCLUSIONS: We believe these findings warrant further study of anti-TAA profiles as biomarkers for primary or early diagnosis of HCC.

Heparin and alkalinized lidocaine versus alkalinized lidocaine for treatment of interstitial cystitis symptoms.

INTRODUCTION: Interstitial cystitis (IC), sometimes referred to as IC/bladder pain syndrome, is a substantial health care problem. Once considered a rare, orphan disease, it is now believed to be relatively common. This pilot study was undertaken to determine if the combination of heparin and alkalinized lidocaine (heparin-lidocaine) was more efficacious than alkalinized lidocaine at relieving pain and urgency symptoms associated with IC and also capable of yielding higher lidocaine absorption. MATERIALS AND METHODS: A single blind study was conducted on 14 IC patients with a heparin-lidocaine combination versus alkalinized lidocaine instilled intravesically. In a separate study serum lidocaine levels for heparin-alkalinized lidocaine combination versus USP lidocaine only were determined by high performance liquid chromatography. RESULTS: Alkalinized lidocaine and heparin have been reported to provide relief from pain and urgency symptoms associated with IC. The heparin-lidocaine combination significantly reduced the % of bladder pain (38% versus 13%, p = 0.029) and urgency (42% versus 8% p = 0.003) compared to lidocaine. In addition the GAR was significantly better for the heparin-lidocaine combination at both 1 hr % improved (77% versus 50%, p = 0.04) and 24 hrs (57% versus 23%, p = 0.002) after study drug treatment. Serum lidocaine levels for the heparin-lidocaine combination were significantly higher compared to USP lidocaine (unalkalinized). The mean +/- SEM was 0.45 +/- 0.09 µg/mL and 0.20 +/- 0.05 µg/mL, respectively (p = 0.019). CONCLUSIONS: In this pilot study the heparin-lidocaine combination results in significantly better relief of IC symptoms compared to alkalinized lidocaine and the combination yields higher lidocaine absorption than USP lidocaine.

Zone-specific gene expression patterns in articular cartilage.

OBJECTIVE: To identify novel genes and pathways specific to the superficial zone (SZ), middle zone (MZ), and deep zone (DZ) of normal articular cartilage. METHODS: Articular cartilage was obtained from the knees of 4 normal human donors. The cartilage zones were dissected on a microtome. RNA was analyzed on human genome arrays. The zone-specific DNA array data obtained from human tissue were compared to array data obtained from bovine cartilage. Genes differentially expressed between zones were evaluated using direct annotation for structural or functional features, and by enrichment analysis for integrated pathways or functions. RESULTS: The greatest differences in genome-wide RNA expression data were between the SZ and DZ in both human and bovine cartilage. The MZ, being a transitional zone between the SZ and DZ, thereby shared some of the same pathways as well as structural/functional features of the adjacent zones. Cellular functions and biologic processes that were enriched in the SZ relative to the DZ included, most prominently, extracellular matrix-receptor interactions, cell adhesion molecule functions, regulation of actin cytoskeleton, ribosome-related functions, and signaling aspects such as the IFN, IL4, Cdc42/Rac, and JAK/STAT signaling pathways. Two pathways were enriched in the DZ relative to the SZ, including PPARG and EGFR/SMRTE. CONCLUSION: These differences in cartilage zonal gene expression identify new markers and pathways that govern the unique differentiation status of chondrocyte subpopulations.

Histopathological changes in the human posterior cruciate ligament during aging and osteoarthritis: correlations with anterior cruciate ligament and cartilage changes.

OBJECTIVES: To determine the histological patterns of posterior cruciate ligament (PCL) degeneration during aging and in relation to changes in articular cartilage and anterior cruciate ligament (ACL) across the entire adult age spectrum. METHODS: Human knee joints (n=120 from 65 donors) were processed within 72 h of postmortem. Articular cartilage surfaces were graded macroscopically. Each PCL was histologically evaluated for inflammation, mucinous changes, chondroid metaplasia, cystic changes and orientation of collagen fibres. The severity of PCL degeneration was classified as normal, mild, moderate or severe. PCL scores were compared to ACL and cartilage scores from the same knees. RESULTS: All knees had intact PCL. Histologically, 6% were normal, 76% showed mild, 12% moderate and 9% severe degeneration. Fibre disorientation was the most prevalent and severe change. Histological grades of PCL and ACL correlated, but significantly fewer PCL than ACL showed severe changes. There was a weaker correlation between aging and total histological PCL scores (R=0.26) compared to aging and ACL scores (R=0.42). ACL scores correlated with cartilage scores (R=0.54) while PCL scores increased with the severity of osteoarthritis from grades 0 to III but not between osteoarthritis grades III-IV (R=0.32). In knees with ruptured ACL, the PCL scores correlated with cartilage scores of the lateral compartment. CONCLUSIONS: PCL histopathological changes were less severe than in the ACL. PCL degeneration was associated with ACL and cartilage damage. The lack of correlation with age indicates independent pathways for PCL versus ACL degeneration.

Worldwide Regional Differences in Obesity, Elderly, and COVID-19 Mortality: Do the Exceptions Prove the Rule?

Objectives: Obesity and old age are commonly assumed to be risk factors for COVID-19 mortality. On a worldwide basis, we examine quantitative measures of obesity and elderly in the populations of individual countries and territories, and investigate whether these measures are predictive of COVID-19 mortality in those countries. In particular, we highlight regional differences relative to obesity and elderly metrics, and how these relate to COVID-19 mortality. Methods: In this retrospective, population-based study, we obtained data relating to percentages of obese or elderly individuals in 199 countries, as well as COVID-19 mortality rates in these countries. We used negative binomial regression analyses to assess associations between COVID-19 mortality rates and the putative risk factors, in six regions - Africa, Asia, Europe, North America, Oceania, and South America. Results: We found significant differences between regions relative to COVID-19 mortality, as well as obesity and elderly population proportions. There were also substantial differences between countries within regions relative to proportions of obesity and elderly individuals, and COVID-19 mortality. Conclusions: There are significant differences both between regions and within regions relative to COVID-19 mortality rates, as well as proportions of obese or elderly individuals. A global pronouncement that obesity and elderly constitute definitive risk factors for COVID-19 mortality masks the subtleties engendered by these intra- and inter-regional differences.

State Government Policy Responses to the COVID-19 Pandemic in the United States 2020-2022: Concordant Heterogeneity?

Objectives: We investigate governmental responses to the COVID-19 pandemic on a statewide basis between January 2020 and June 2022, together with mortality rates attributable to COVID-19 over the same period. Our aim is to demarcate the states' responses, and examine whether these differential responses are associated with COVID-19 mortality. Methods: Our study is based on individual state data from the Oxford COVID-19 Government Response Tracker, OxCGRT. We focus on the Government Response Index, the most comprehensive index tracked in the OxCGRT dataset. We use multivariate techniques to group the states into clusters relative to their similarities on the Government Response Index, and determine mortality rates attributable to COVID-19 in the individual groups. Results: We find that the Government Response Index was sustained at relatively constant levels in the states, with two major transition periods: a rapid rise in stringency during April through June of 2020, and a gradual decline in May and June of 2021. Heterogeneity in the Government Response Index dramatically increased in 2022. No consistent patterns emerge when relating government stringency measures with COVID-19 mortality rates. Conclusions: There is inconsistent evidence that increased governmental stringency is associated with lower COVID-19 mortality; judicious selection of time frames can lead to contrasting inferences. Political trends and motivations appear to have an outsized influence on governmental responses to the COVID-19 public health crisis, to the detriment of the populace.

Déjà vu all over again: racial, ethnic and age disparities in mortality from influenza 1918-19 and COVID-19 in the United States.

Background: Examination of the mortality patterns in the United States among racial, ethnic, and age groups attributed to the 1918-19 influenza pandemic revealed stark disparities, causes for which could have been addressed and rectified this past century. However, these disparities have been amplified during the current COVID-19 pandemic.We have ignored the lessons of the past, and were destined to repeat its failings. Objectives: Compare and contrast mortality patterns by age, race, and ethnicity attributable to the 1918-19 influenza pandemic in the United States with corresponding patterns during the COVID-19 pandemic. Methods: This is a retrospective study, establishing mortality rates according to age, race and ethnicity attributable to the 1918-19 influenza pandemic in the United States and to the current COVID-19 pandemic, using mortality data published by the U.S. Public Health Service and the Centers for Disease Control and Prevention. Negative binomial regression models were used to establish rate ratios, that is, ratios of mortality rates across the various racial/ethnic groups, and associated 95% confidence intervals. Results: Mortality patterns by age differ significantly between the 1918-19 influenza pandemic and the COVID-19 pandemic: with infant and young adult (25-40 years old) mortality substantially higher in the former. Disparities in mortality between racial and ethnic groups are amplified in the COVID-19 pandemic compared to the 1918-19 experience. Conclusions: As we evaluate our nation's response to COVID-19 and design public policy to prepare better for coming pandemics, we cannot ignore the stark disparities in mortality rates experienced by different racial and ethnic groups. This will require a sustained resolve by society and government to delineate and remedy the causative factors, through science devoid of political interpretation and exploitation.

Intracerebral hemorrhage and thrombin-induced alterations in cerebral microvessel matrix.

Four phase III clinical trials of oral direct factor Xa or thrombin inhibitors demonstrated significantly lower intracranial hemorrhage compared to warfarin in patients with nonvalvular-atrial fibrillation. This is counter-intuitive to the principle that inhibiting thrombosis should increase hemorrhagic risk. We tested the novel hypothesis that anti-thrombin activity decreases the risk of intracerebral hemorrhage by directly inhibiting thrombin-mediated degradation of cerebral microvessel basal lamina matrix, responsible for preventing hemorrhage. Collagen IV, laminin, and perlecan each contain one or more copies of the unique α-thrombin cleavage site consensus sequence. In blinded controlled experiments, α-thrombin significantly degraded each matrix protein in vitro and in vivo in a concentration-dependent fashion. In vivo stereotaxic injection of α-thrombin significantly increased permeability, local IgG extravasation, and hemoglobin (Hgb) deposition together with microvessel matrix degradation in a mouse model. In all formats the direct anti-thrombin dabigatran completely inhibited matrix degradation by α-thrombin. Fourteen-day oral exposure to dabigatran etexilate-containing chow completely inhibited matrix degradation, the permeability to large molecules, and cerebral hemorrhage associated with α-thrombin. These experiments demonstrate that thrombin can degrade microvessel matrix, leading to hemorrhage, and that inhibition of microvessel matrix degradation by α-thrombin decreases cerebral hemorrhage. Implications for focal ischemia and other conditions are discussed.

Kidney preservation by bone marrow cell transplantation in hereditary nephropathy.

The prospect of cell-based therapy for kidney disease remains controversial despite its immense promise. We had previously shown that transplanting bone marrow and hematopoietic stem cells could generate renal cells and lead to the preservation of kidney function in a mouse model for cystinosis (Ctns(-/-)) that develops chronic kidney injury, 4 months post transplantation. Here, we determined the long-term effects of bone marrow stem cell transplantation on the kidney disease of Ctns(-/-) mice 7 to 15 months post transplantation. Transfer of bone marrow stem cells expressing a functional Ctns gene provided long-term protection to the kidney. Effective therapy, however, depended on achieving a relatively high level of donor-derived blood cell engraftment of Ctns-expressing cells, which was directly linked to the quantity of these cells within the kidney. In contrast, kidney preservation was dependent neither on renal cystine content nor on the age of the mice at the time of transplant. Most of the bone marrow-derived cells within the kidney were interstitial and not epithelial, suggesting that the mechanism involved an indirect protection of the tubules. Thus, our model may help in developing strategies to enhance the potential success of cell-based therapy for kidney injury and in understanding some of the discrepancies currently existing in the field.

Lessons from the Past: Methodological Issues Arising from Comparison of the Disease Burden of the Influenza A (H1N1) Pandemic 2009-10 and Seasonal Influenza 2010-2019 in the United States.

BACKGROUND: Annual influenza outbreaks constitute a major public health concern, both in the United States and worldwide. Comparisons of the health burdens of outbreaks might lead to the identification of specific at-risk populations, for whom public health resources should be marshaled appropriately and equitably. METHODS: We examined the disease burden of the 2009-10 influenza A (H1N1) pandemic relating to illnesses, medical visits, hospitalizations, and mortality, compared to influenza seasons 2010 to 2019, in the United States, as compiled by the Centers for Disease Control. RESULTS: With regard to seasonal influenza, rates of illnesses and medical visits were highest in infants aged 0-4 years, followed by adults aged 50-64 years. Rates of hospitalizations and deaths evinced a starkly different pattern, both dominated by elderly adults aged 65 and over. Youths aged 0 to 17 years were especially adversely affected by the H1N1 pandemic relative to hospitalizations and mortality compared to seasonal influenza; but curiously the opposite pattern was observed in elderly adults (aged 65 and older). CONCLUSIONS: Determination of a baseline influenza mortality profile in the United States over the 2010-19 decade is not straightforward. The disease burden of the 2009-10 influenza A pandemic among the elderly was strikingly unlike that observed in the subsequent influenza seasons 2010 to 2019: the past did not predict the future.

A Note on Excess Mortality Attributable to COVID-19 in the United States.

Background: Annual influenza outbreaks constitute a major public health concern in the United States. But this health burden appears dwarfed by the impact of COVID-19. Our aim is to quantify the excess mortality attributable to COVID-19, compared to previous influenza seasons. Methods: We retrospectively compare weekly mortality figures attributable to influenza and pneumonia in the United States from 2013 to 2019 with corresponding figures attributable to influenza, pneumonia, and COVID-19 from 2019 to 2021. We utilize a difference in differences regression methodology to estimate excess mortality observed in 2019-21 compared to 2013-2019. Results: Mortality patterns attributable to influenza, pneumonia, and COVID-19 differ significantly from the 2013-19 experience. Notably, distinct, aperiodic mortality waves occur in the 2019-2021 window, and mortality is well in excess of what is observed in typical influenza seasons. Conclusions: The COVID-19 pandemic has led to considerable excess mortality in the United States, and has strained public health resources. One might expect that the mortality waves observed during the pandemic will be damped by increasing levels of vaccination, and prior infections.

The wisdom of the commons: ensemble tree classifiers for prostate cancer prognosis.

MOTIVATION: Classification and regression trees have long been used for cancer diagnosis and prognosis. Nevertheless, instability and variable selection bias, as well as overfitting, are well-known problems of tree-based methods. In this article, we investigate whether ensemble tree classifiers can ameliorate these difficulties, using data from two recent studies of radical prostatectomy in prostate cancer. RESULTS: Using time to progression following prostatectomy as the relevant clinical endpoint, we found that ensemble tree classifiers robustly and reproducibly identified three subgroups of patients in the two clinical datasets: non-progressors, early progressors and late progressors. Moreover, the consensus classifications were independent predictors of time to progression compared to known clinical prognostic factors.

A Note on Calibration of Clinical Prediction Models with Copas Statistics.

Background: Calibration of clinical prediction models often entails assessing goodness of fit with independent, non-identically distributed Bernoulli random variables. We here investigate two statistics studied by Copas in this setting. Materials and Methods: We present distribution theory and a simulation study to compare the operating characteristics of the Copas statistics. Results: In our simulation study with relatively small sample sizes, we found a simple Cornish-Fisher approximation tail quantiles of the distributions of the Copas statistics to perform adequately. Upon illustrating their use in a calibration study relating to prediction of atherosclerotic cardiovascular disease risk, power properties appear to reflect differential weighting accorded to observations, as evinced with other goodness-of-fit statistics. Conclusion: The Copas statistics are easily implemented, have proven value in other contexts, and appear to be underutilized in calibration studies. They ought to be part of the armamentarium of calibration tools for all researchers.

Impact of Cisplatin Dosing Regimens on Mammary Tumor Growth in an Animal Model.

BACKGROUND: We have recently introduced a modification of the seminal Simeoni model for tumor growth, the modification entailing the incorporation of delay differential equations into its formulation. We found that the modification was competitive with the Simeoni construct in modeling mammary tumor growth under cisplatin treatment in an animal model. METHODS: In our original study, we had two cohorts of animals: untreated, and treatment with bolus injection of cisplatin on day 0. We here explore how modifications in the cisplatin dosing scheme affect tumor growth in our model. RESULTS: We found that modest fractionation dosing schemes have little ultimate impact on tumor growth. In contrast, metronomic dosing schemes seem quite efficacious, and might yield effective control over tumor progression. CONCLUSIONS: With regard to cisplatin as single agent chemotherapy, a minimum level of drug for a prolonged period of time seems more critical than rapid achievement of a very high dose for a shorter time frame for deterring tumor growth or progression. Exploration of tumor dose schedules with mathematical models can provide valuable insights into potentially effective therapeutic regimens.

The Immunosuppressive Microenvironment in BRCA1-IRIS-Overexpressing TNBC Tumors Is Induced by Bidirectional Interaction with Tumor-Associated Macrophages.

Tumor-associated macrophages (TAM) promote triple-negative breast cancer (TNBC) progression. Here, we report BRCA1-IRIS-overexpressing (IRISOE) TNBC cells secrete high levels of GM-CSF in a hypoxia-inducible factor-1α (HIF1α)- and a NF-κB-dependent manner to recruit macrophages to IRISOE cells and polarize them to protumor M2 TAMs. GM-CSF triggered TGFß1 expression by M2 TAMs by activating STAT5, NF-κB, and/or ERK signaling. Despite expressing high levels of TGFß1 receptors on their surface, IRISOE TNBC cells channeled TGFß1/TßRI/II signaling toward AKT, not SMAD, which activated stemness/EMT phenotypes. In orthotopic and syngeneic mouse models, silencing or inactivating IRIS in TNBC cells lowered the levels of circulating GM-CSF, suppressed TAM recruitment, and decreased the levels of circulating TGFß1. Coinjecting macrophages with IRISOE TNBC cells induced earlier metastasis in athymic mice accompanied by high levels of circulating GM-CSF and TGFß1. IRISOE TNBC cells expressed low levels of calreticulin (the "eat me" signal for macrophages) and high levels of CD47 (the "do not eat me" signal for macrophages) and PD-L1 (a T-cell inactivator) on their surface. Accordingly, IRISOE TNBC tumors had significantly few CD8+/PD-1+ cytotoxic T cells and more CD25+/FOXP3+ regulatory T cells. These data show that the bidirectional interaction between IRISOE cells and macrophages triggers an immunosuppressive microenvironment within TNBC tumors that is favorable for the generation of immune-evading/stem-like/IRISOE TNBC metastatic precursors. Inhibiting this interaction may inhibit disease progression and enhance patients' overall survival. SIGNIFICANCE: The BRCA1-IRIS oncogene promotes breast cancer aggressiveness by recruiting macrophages and promoting their M2 polarization.

Predictors of intracerebral hemorrhage severity and its outcome in Japanese stroke patients.

OBJECTIVE: The aim of this investigation was to determine the factors influencing acute intracerebral hemorrhage severity on admission and clinical outcomes at discharge. METHODS: Sixty acute stroke hospitals throughout Japan participated in the Japan Standard Stroke Registry Study (JSSRS), documenting the in-hospital course of 16,630 consecutive patients with acute stroke from January 2001 to March 2004. We identified 2,840 adult patients from the JSSRS who had intracerebral hemorrhage. RESULTS: Intracerebral hemorrhage severity on admission was strongly related to age, previous stroke history, and hemorrhage size in a monotone fashion [chi(2)(9) = 374.5, p < 0.0001]. Drinking history was also predictive of intracerebral hemorrhage severity on admission, but the association was not monotone. Interestingly, intracerebral hemorrhage severity on admission was increased in nondrinking and heavy drinking compared to mild drinking (p < 0.05). Unsuccessful outcome (modified Rankin scale score = 3-6) was related to age, previous stroke history, hemorrhage size, and intracerebral hemorrhage severity on admission [chi(2)(9) = 830.4, p < 0.0001]. Mortality was related to hemorrhage size, intraventricular hemorrhage, intracerebral hemorrhage severity on admission, and surgical operation [chi(2)(7) = 540.4, p < 0.0001]. CONCLUSION: We could find four varied factors associated with intracerebral hemorrhage severity and its outcomes. Interestingly, intracerebral hemorrhage severity tended to be greater in nondrinking and heavy drinking than mild drinking. Additionally, surgical operation decreased intracerebral hemorrhage mortality.

The concordance index C and the Mann-Whitney parameter Pr(X>Y) with randomly censored data.

Harrell's c-index or concordance C has been widely used as a measure of separation of two survival distributions. In the absence of censored data, the c-index estimates the Mann-Whitney parameter Pr(X>Y), which has been repeatedly utilized in various statistical contexts. In the presence of randomly censored data, the c-index no longer estimates Pr(X>Y); rather, a parameter that involves the underlying censoring distributions. This is in contrast to Efron's maximum likelihood estimator of the Mann-Whitney parameter, which is recommended in the setting of random censorship.

PEA-15 inhibits tumor cell invasion by binding to extracellular signal-regulated kinase 1/2.

Phosphoprotein enriched in astrocytes of 15 kDa (PEA-15) binds to extracellular signal-regulated kinase 1 and 2 (ERK1/2) mitogen-activated protein (MAP) kinases to alter ERK1/2 cellular localization and target preferences and binds to adaptors in the extrinsic cell death pathway to block apoptosis. Here, we report that PEA-15 protein expression is inversely correlated with the invasive behavior of breast cancer in an immunohistochemical analysis of a breast cancer progression tissue microarray. Short hairpin RNA-mediated inhibition of PEA-15 expression increased the invasion of PEA-15-expressing tumor cells in vitro, suggesting a causative role for PEA-15 in the inhibition of invasion. This causative role was confirmed by the finding that the enforced expression of PEA-15 in invasive tumor cells reduced invasion. The effect of PEA-15 on tumor invasion is mediated by its interaction with ERK1/2 as shown by the following: (a) PEA-15 mutants that fail to bind ERK1/2 did not inhibit invasion; (b) overexpression of ERK1 or activated MAP/ERK kinase (MEK) reversed the inhibitory effect of PEA-15; (c) when an inhibitor of ERK1/2 activation reduced invasion, PEA-15 expression did not significantly reduce invasion further. Furthermore, we find that the effect of PEA-15 on invasion seems to relate to the nuclear localization of activated ERK1/2. PEA-15 inhibits invasion by keeping ERK out of the nucleus, as a PEA-15 mutant that cannot prevent ERK nuclear localization was not able to inhibit invasion. In addition, membrane-localized ERK1, which sequesters endogenous ERK1 to prevent its nuclear localization, also inhibited invasion. These results reveal that PEA-15 regulates cancer cell invasion via its ability to bind ERK1/2 and indicate that nuclear entry of ERK1/2 is important in tumor behavior.