The Significance of Thyroid Hormone Receptors in Breast Cancer: A Hypothesis-Generating Narrative Review.

BACKGROUND: Breast cancer (BC) is frequently diagnosed among Canadian women. While targeted therapies are available for most BC patients; treatment resistance is common and novel therapeutic targets are of interest. Thyroid hormones (TH) bound to thyroid hormone receptors (THR) influence cell proliferation and differentiation; they are also involved in the growth and development of normal breast tissue. Evidence suggests that THRß is a tumor suppressor in various solid tumors. PURPOSE: This narrative review discusses retrospective studies regarding the clinical relevance of THRß as a potential prognostic biomarker and therapeutic target in BC. METHODS: We consulted with an information specialist to develop a search strategy to find all literature related to THRα expression as a potential prognostic and therapeutic biomarker in breast cancer. The primary search was developed for Medline and translated to Embase. The searches were conducted on the Ovid platform on 18 August 2023. RESULTS: Across seven retrospective studies identified, several have shown an association between higher THRß1 expression with a lower risk of BC recurrence and with longer overall survival. CONCLUSIONS: Some evidence suggests that THRß expression is associated with a lower risk of BC recurrence and death. Validation of THRß as an independent prognostic biomarker and possible predictive biomarker of response to endocrine therapy and/or chemotherapy is of interest. Given that THRß is upstream of the AKT/PI3K pathway, its potential as a predictive biomarker of response to AKT inhibitors and/or PI3K inhibitors may also be of value. Finally, the potential re-purposing of THRß agonists as anti-cancer agents warrants investigation.

Association of extended core sampling with delayed intervention and pathologic outcomes for active surveillance patients: A population-based analysis.

INTRODUCTION: Combined systematic plus targeted biopsy sampling improves detection of clinically significant prostate cancer (PCa). Our objective was to evaluate whether extended core sampling at initial biopsy in active surveillance (AS) patients is associated with subsequent AS discontinuation and pathologic outcomes. METHODS: National Comprehensive Cancer Network (NCCN) low- and favorableintermediate-risk (FIR) AS patients diagnosed between 2010 and 2015 were identified from the Surveillance, Epidemiology, and End Results (SEER) Prostate with Watchful Waiting database. Prostate biopsy sampling was operationalized as: standard (10-12 cores), extended (13-20 cores), or super-extended (21+ cores). Sensitivity analyses using differing cutoffs was performed. Outcomes included delayed definitive intervention (radical prostatectomy [RP]/radiotherapy) and pathologic upgrading and/or downgrading in delayed RP patients. Multivariable logistic regression modelling adjusted for sociodemographic/oncologic variables was performed. RESULTS: This cohort included 42 459 patients (low-risk: 28 411; FIR:14 048); 25-29% and 3- 5% of patients underwent extended and super-extended core sampling, respectively, at diagnosis. Extended core sampling was associated with decreased odds of definitive intervention in low (odds ratio [OR] 0.89, p=0.003) and grade group 2 (GG2) FIR (OR 0.83, p=0.002) patients. Super-extended sampling was associated with decreased odds of definitive intervention in PSA 10-20 FIR patients (OR 0.65, p=0.02). Super-extended sampling was associated with decreased odds of upgrading to ≥GG2 disease in low-risk (OR 0.45, p=0.032) and to ≥GG3 disease in GG2 FIR patients (OR 0.67, p=0.044). CONCLUSIONS: This population-based analysis demonstrates that extended/super-extended sampling at diagnosis is associated with significantly decreased odds of AS discontinuation and pathologic upgrading in low/FIR AS patients. This highlights the significance of extended tissue sampling at initial biopsy to appropriately risk-stratify AS patients and minimize AS discontinuation rates.

Intraductal Prostate Cancer Affinity for Lymphatic-Predominant Metastases Through 18F-DCFPyL‒Prostate-Specific Membrane Antigen‒Positron Emission Tomography/CT Scans in Pretreatment Prostate Cancer Patients.

PURPOSE: Intraductal prostate cancer (IDC) is linked to unfavorable oncologic outcomes, marked by distinctive cellular intrinsic pathway changes and intricate immunosuppressive microenvironments that could impact the way cancer spreads. The aim of this study was to determine whether the presence of IDC in prostate biopsy specimens obtained from patients before primary prostate cancer (PCa) treatment is associated with a lymph node metastatic propensity in prostate-specific membrane antigen (PSMA)‒positron emission tomography (PET)/CT. MATERIALS AND METHODS: This was a cross-sectional analysis of all PCa patients undergoing a pretreatment 18F-DCFPyL-PSMA-PET/CT between January 1, 2016, and August 2021 at The Princess Margaret Cancer Centre. Outcomes were presence of any metastasis in the overall cohort, presence of lymphatic vs no metastases, and presence of lymphatic vs bone metastasis among patients who underwent PSMA-PET/CT as PCa primary staging. The associations between IDC presence on the prostate biopsy and the study outcomes were evaluated using univariable and multivariable logistic regression analyses. RESULTS: The cohort consisted of 120 patients. IDC and cribriform pattern were observed in 55 (46%) and 48 (40%) prostate biopsies, respectively. Overall, 52 patients (43%) had evidence of metastasis. Presence of IDC on biopsy was associated with increased odds of overall metastasis (odds ratio: 2.47, 95% CI: 1.09-5.61, P = .03). Of the 52 patients with evidence of metastasis, 41 (79%) had evidence of lymphatic metastasis. Presence of IDC on biopsy was associated with significantly increased odds of lymphatic metastasis vs nonmetastases (odds ratio: 3.03, 95% CI: 1.24-7.40, P = .01). CONCLUSIONS: The identification of IDC morphology in prostate biopsy specimens has been observed to be significantly linked with lymph node metastasis on 18F-DCFPyL-PET/CT imaging in a PCa pretreatment staging setting. We found that presence of IDC in prostate biopsy appears to be a marker for lymph node metastasis on 18F-DCFPyL-PET/CT.

Limitations of Prostate Biopsy in Detection of Cribriform and Intraductal Prostate Cancer.

BACKGROUND: The presence of cribriform morphology and intraductal carcinoma (IDC) in prostate biopsies and radical prostatectomy specimens is an adverse prognostic feature that can be used to guide treatment decisions. OBJECTIVE: To assess how accurately biopsies can detect cribriform morphology and IDC cancer by examining matched biopsy and prostatectomy samples. DESIGN, SETTING, AND PARTICIPANTS: Patients who underwent radical prostatectomy at The Princess Margaret Cancer Centre between January 2015 and December 2022 and had cribriform morphology and/or IDC in the surgical specimen were included in the study. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: We used detection sensitivity to evaluate the level of agreement between biopsy and prostatectomy samples regarding the presence of cribriform morphology and IDC. RESULTS AND LIMITATIONS: Of the 287 men who underwent radical prostatectomy, 241 (84%) had cribriform morphology and 161 (56%) had IDC on final pathology. The sensitivity of prostate biopsy, using radical prostatectomy as the reference, was 42.4% (95% confidence interval [CI] 36-49%) for detection of cribriform morphology and 44.1% (95% CI 36-52%) for detection of IDC. The sensitivity of prostate biopsy for detection of either IDC or cribriform morphology was 52.5% (95% CI 47-58%). Among patients who underwent multiparametric magnetic resonance imaging-guided biopsies, the sensitivity was 54% (95% CI 39-68%) for detection of cribriform morphology and 37% (95% CI 19-58%) for detection of IDC. CONCLUSIONS: Biopsy has low sensitivity for detecting cribriform morphology and IDC. These limitations should be incorporated into clinical decision-making. Biomarkers for better detection of these histological patterns are needed. PATIENT SUMMARY: Prostate biopsy is not an accurate method for detecting two specific types of prostate cancer cells, called cribriform pattern and intraductal prostate cancer, which are associated with unfavorable prognosis.

Mesorectal nodal metastasis with seminal vesicle invasion in biochemically recurrent prostate cancer.

OBJECTIVES: To determine the prevalence and predictors of mesorectal lymph node (MLN) metastases on prostate-specific membrane antigen (PSMA)-based positron emission tomography/computed tomography (PET/CT) in patients with biochemically recurrent prostate cancer (PCa) following radical therapy. MATERIALS AND METHODS: This was a cross-sectional analysis of all PCa patients with biochemical failure following radical prostatectomy or radiotherapy who underwent an 18 F-DCFPyL-PSMA-PET/CT at the Princess Margaret Cancer Centre between December 2018 and February 2021. Lesions with PSMA scores ≥2 were considered positive for PCa involvement (PROMISE classification). Predictors of MLN metastasis were evaluated using univariable and multivariable logistic regression analyses. RESULTS: Our cohort consisted of 686 patients. The primary treatment method was radical prostatectomy and radiotherapy in 528 (77.0%) and 158 patients (23.0%), respectively. The median serum PSA level was 1.15 ng/mL. Overall, 384 patients (56.0%) had a positive scan. Seventy-eight patients (11.3%) had MLN metastasis, with 48/78 (61.5%) having MLN involvement as the only site of metastasis. On multivariable analysis, presence of pT3b disease (odds ratio 4.31, 95% confidence interval 1.44-14.2; P = 0.011) was significantly associated with increased odds of MLN metastasis, whereas surgical factors (radical prostatectomy vs radiotherapy; performance/extent of pelvic nodal dissection), surgical margin positivity, and Gleason Grade were not. CONCLUSIONS: In this study, 11.3% of PCa patients with biochemical failure had MLN metastasis on 18 F-DCFPyL-PET/CT. pT3b disease was associated with 4.31-fold significantly increased odds of MLN metastasis. These findings suggest alternate drainage routes for PCa cells, either via alternate lymphatic drainage from the seminal vesicles themselves or secondary to direct extension from posteriorly located tumours invading the seminal vesicles.

Lymphotropic Pattern of Prostate-specific Membrane Antigen-detected Metastases Among Biochemically Recurrent Radical Prostatectomy Patients with Cribriform Disease.

BACKGROUND: Cribriform morphology portends worse oncologic outcomes, and has unique cellular intrinsic pathway alterations and tumor microenvironments that may impact metastatic spread patterns. OBJECTIVE: To determine whether the presence of cribriform morphology in prostatectomy specimens of patients with biochemical recurrence after radical prostatectomy (RP) is associated with the presence of metastasis on prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) and a distinct pattern of spread. DESIGN, SETTING, AND PARTICIPANTS: A cross-sectional analysis was conducted of all prostate cancer patients with biochemical recurrence after RP undergoing 18F-DCFPyL-PET/CT between December 2018 and February 2021 at the Princess Margaret Cancer Centre. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: Outcomes were presence of any metastasis in the overall cohort and lymphatic versus bone/visceral metastases among patients with metastatic disease. The associations between the presence of intraductal (IDC) and/or invasive cribriform (ICC) carcinoma on the RP specimen and study outcomes were evaluated using logistic regression analyses. RESULTS AND LIMITATIONS: The cohort included 176 patients. IDC and ICC were observed in 77 (43.8%) and 80 (45.5%) RP specimens, respectively. The median time from RP to PSMA-PET/CT was 5.0 yr. The median serum prostate-specific antigen level at PSMA-PET/CT was 1.12 ng/ml. Overall, metastasis was observed in 77 patients, of whom 58 were had lymphatic-only metastasis. On a multivariable analysis, presence of IDC on RP was associated with increased odds of overall metastasis (odds ratio [OR]: 2.17; 95% confidence interval [CI]: 1.07-4.45; p = 0.033). Presence of ICC on RP was associated with significantly increased odds of lymphatic versus bone/visceral metastases (OR: 3.13; 95% CI: 1.09-21.7; p = 0.004). CONCLUSIONS: Presence of cribriform morphology on RP specimens of patients with biochemical failure after RP is associated with increased odds of PSMA-PET/CT-detected metastases with a lymphatic predominant pattern of spread. These findings have implications for the design and evaluation of post-RP salvage therapies. PATIENT SUMMARY: We found that microscopic cribriform appearance correlates with disease spread on imaging in prostate cancer patients with recurrence and has a predilection for spread to lymph nodes, as opposed to bone or visceral organs.

Mental health and self-determination profiles of the diverse population of medical students in Malaysia during the COVID-19 pandemic.

INTRODUCTION: Medical schools throughout the world were forced to modify their programming during the COVID-19 pandemic. In Malaysia, virtual learning plans were implemented for non-clinical programming, while clinical posting modifications were designed to meet local SOPs. The prolonged enforcement of these modifications to undergraduate medical education will have affected student experiences, including well-being. Since these feelings can relate to perceived relatedness, autonomy, and competence, it is important to identify any potential factors that may lead to reduced intrinsic motivation in students. It is also important to consider how demographic features may contribute to student perspectives, which can be studied using the unique diversity represented by Malaysian students. METHODS: A quantitative survey was distributed to Malaysian medical students to assess their overall wellbeing, autonomy in educational decision making, student experiences, and position on changes to graduation timing. Intrinsic components were identified using Principal Component Analysis and were aligned with the three needs for self-determination, namely relatedness, autonomy, and competence. Finally, trends in responses for participants from various sub-populations were assessed using ANOVA testing. RESULTS: Responses were collected from 442 students representing 23 accredited Malaysian medical schools. Upon validation and reliability testing, eight components were identified with themes relating to: mental health, social concerns, communication, timing of modifications, depth of learning, and student-centred learning. Of these, gender was related to mental health, student-centred learning, and delayed graduation, while stage was related to student-centred learning and delayed graduation in addition to concerns about depth of learning and timing of modifications. Interestingly, ethnicity was related to differences in opinions about delayed graduation and income was related to social concerns. CONCLUSION: The results of this study indicate that, while students were satisfied in general with the content and delivery of their programmes given the circumstances, there is evidence to suggest negative effects on emotional wellbeing and expression of student voice, due to the modifications that were made. Additionally, these feelings related to the three motivational needs, suggesting that students were experiencing a dampened motivational profile during the pandemic. Further, motivational profiles were distinct between student sub-groups, providing insight for developing appropriate and inclusive accommodations moving forward.

The Antiarrhythmic Drug, Dronedarone, Demonstrates Cytotoxic Effects in Breast Cancer Independent of Thyroid Hormone Receptor Alpha 1 (THRα1) Antagonism.

Previous research has suggested that thyroid hormone receptor alpha 1 (THRα1), a hormone responsive splice variant, may play a role in breast cancer progression. Whether THRα1 can be exploited for anti-cancer therapy is unknown. The antiproliferative and antitumor effects of dronedarone, an FDA-approved anti-arrhythmic drug which has been shown to antagonize THRα1, was evaluated in breast cancer cell lines in vitro and in vivo. The THRα1 splice variant and the entire receptor, THRα, were also independently targeted using siRNA to determine the effect of target knockdown in vitro. In our study, dronedarone demonstrates cytotoxic effects in vitro and in vivo in breast cancer cell lines at doses and concentrations that may be clinically relevant. However, knockdown of either THRα1 or THRα did not cause substantial anti-proliferative or cytotoxic effects in vitro, nor did it alter the sensitivity to dronedarone. Thus, we conclude that dronedarone's cytotoxic effect in breast cancer cell lines are independent of THRα or THRα1 antagonism. Further, the depletion of THRα or THRα1 does not affect cell viability or proliferation. Characterizing the mechanism of dronedarone's anti-tumor action may facilitate drug repurposing or the development of new anti-cancer agents.

Polycomb complex protein BMI1 confers resistance to tamoxifen in estrogen receptor positive breast cancer.

We report that BMI1 promotes tamoxifen resistance in estrogen receptor (ER)-positive breast cancer (BC). BMI1 overexpression conferred MCF7 and TD47 cells resistance to tamoxifen; BMI1 knockdown sensitized the process. In MCF7-derived tamoxifen resistant cells, BMI1 expression was upregulated and BMI1 knockdown reduced the resistance. BMI1 is an oncogene; its oncogenic activity is attributed to BMI1-stimulated E3 ubiquitin ligase activity, a process that requires BMI1's ring finger (RF) domain. However, a BMI1 mutant without RF conferred tamoxifen resistance. Tamoxifen significantly reduced the growth of xenografts derived from MCF7 cells, but accelerated the growth of tumors produced by BMI1 overexpressing MCF7 cells. BMI1 enhances the pathways that promote resistance to endocrine therapy, including ER, androgen receptor, and MUC1. In patients with ER + BCs (n = 177), BMI1 expression was associated with BC recurrence. In the Curtis dataset consisting of ER + BCs (n = 1506) and ER- BCs (n = 474; cBioPortal), upregulations in BMI1 mRNA expression were correlated with ER + BCs; the upregulation was associated with a set of differentially expressed genes (DEGs). These DEGs were enriched with reductions in immunological processes, indicating a role of BMI1 in downregulation of the immune surveillance.

Differential roles of RET isoforms in medullary and papillary thyroid carcinomas.

The RET receptor tyrosine kinase mediates cell proliferation, survival and migration in embryogenesis and is implicated in the transformation and tumour progression in multiple cancers. RET is frequently mutated and constitutively activated in familial and sporadic thyroid carcinomas. As a result of alternative splicing, RET is expressed as two protein isoforms, RET9 and RET51, which differ in their unique C-terminal amino acids. These isoforms have distinct intracellular trafficking and associated signalling complexes, but functional differences are not well defined. We used shRNA-mediated knockdown (KD) of individual RET isoforms or of total RET to evaluate their functional contributions in thyroid carcinoma cells. We showed that RET is required for cell survival in medullary (MTC) but not papillary thyroid carcinoma (PTC) cells. In PTC cells, RET depletion reduced cell migration and induced a flattened epithelial-like morphology. RET KD decreased the expression of mesenchymal markers and matrix metalloproteinases and reduced anoikis resistance and invasive potential. Further, we showed that RET51 depletion had significantly greater effects on each of these processes than RET9 depletion in both MTC and PTC cells. Finally, we showed that expression of RET, particularly RET51, was correlated with malignancy in a panel of human thyroid tumour tissues. Together, our data show that RET expression promotes a more mesenchymal phenotype with reduced cell-cell adhesion and increased invasiveness in PTC cell models, but is more important for tumour cell survival, proliferation and anoikis resistance in MTC models. Our data suggest that the RET51 isoform plays a more prominent role in mediating these processes compared to RET9.

The effects of lymph node status on predicting outcome in ER+ /HER2- tamoxifen treated breast cancer patients using gene signatures.

BACKGROUND: Lymph node (LN) status is the most important prognostic variable used to guide ER positive (+) breast cancer treatment. While a positive nodal status is traditionally associated with a poor prognosis, a subset of these patients respond well to treatment and achieve long-term survival. Several gene signatures have been established as a means of predicting outcome of breast cancer patients, but the development and indication for use of these assays varies. Here we compare the capacity of two approved gene signatures and a third novel signature to predict outcome in distinct LN negative (-) and LN+ populations. We also examine biological differences between tumours associated with LN- and LN+ disease. METHODS: Gene expression data from publically available data sets was used to compare the ability of Oncotype DX and Prosigna to predict Distant Metastasis Free Survival (DMFS) using an in silico platform. A novel gene signature (Ellen) was developed by including patients with both LN- and LN+ disease and using Prediction Analysis of Microarrays (PAM) software. Gene Set Enrichment Analysis (GSEA) was used to determine biological pathways associated with patient outcome in both LN- and LN+ tumors. RESULTS: The Oncotype DX gene signature, which only used LN- patients during development, significantly predicted outcome in LN- patients, but not LN+ patients. The Prosigna gene signature, which included both LN- and LN+ patients during development, predicted outcome in both LN- and LN+ patient groups. Ellen was also able to predict outcome in both LN- and LN+ patient groups. GSEA suggested that epigenetic modification may be related to poor outcome in LN- disease, whereas immune response may be related to good outcome in LN+ disease. CONCLUSIONS: We demonstrate the importance of incorporating lymph node status during the development of prognostic gene signatures. Ellen may be a useful tool to predict outcome of patients regardless of lymph node status, or for those with unknown lymph node status. Finally we present candidate biological processes, unique to LN- and LN+ disease, that may indicate risk of relapse.

Identification and evaluation of network modules for the prognosis of basal-like breast cancer.

PURPOSE: Basal-like breast cancer (BLBC) is a molecular subtype of breast cancer associated with poor clinical outcome, although some patients with BLBC experience long-term survival. Apart from nodal status, current clinical/histopathological variables show little capacity to identify BLBC patients at either high- or low-risk of disease recurrence. Accordingly, we sought to develop a network based genomic predictor for predicting the outcome of patients with BLBC. EXPERIMENTAL DESIGN: We performed network analysis on global gene expression profiling data of BLBCs, and identified BLBC network modules associated with AP-1 transcription, G-protein coupled receptors, and T-, B-, and NK-cells that are significant predictors of BLBC patient survival. RESULTS: In gene expression and tissue microarray (TMA) validation cohorts of 210 and 102 BLBC patients, respectively, the identified network modules were robustly associated with patient outcome. In the gene expression validation cohort, the Kaplan-Meier estimate for 10-year survival in the low-risk group was 90%, whereas in the high-risk group it was a 56%. In the TMA cohort, the Kaplan-Meier estimate for 10-year survival in the low-risk group was 98%, whereas in the high-risk group it was 71%. CONCLUSIONS: The capacity to distinguish between patients with BLBC at high- or low-risk of recurrence at the time of diagnosis could permit timely intervention with more aggressive therapeutic regimens in those patients predicted to be high-risk, and to avoid such therapy in low-risk patients.

Thyroid hormone receptor α in breast cancer: prognostic and therapeutic implications.

We determined the expression of two transcriptional variants of thyroid hormone receptor alpha (THRα1 and THRα2) in samples from a cohort of breast cancer patients and correlated expression levels with survival. 130 women who were diagnosed with invasive breast carcinoma between 2007 and 2008 were included. Representative sections of their tumours were analyzed in triplicate on a tissue microarray for expression of THRα1 and THRα2 by immunohistochemistry. The prognostic significance of THRα1 and THRα2 expression was assessed using Kaplan-Meier survival analyses, adjusted for known prognostic factors. Seventy-four percent of tumours had high expression of THRα1 (Allred score ≥6) and 40 % had high expression of THRα2. Expression of THRα2 correlated positively with ER expression (p < 0.001) and with PR expression (p < 0.001), but negatively with HER2 expression (p = 0.018). Patients with low THRα2 expression had inferior 5-year overall survival (75.3 %) compared to those with high expression (91.7 %; p = 0.06). In a multivariate model, high THRα2 expression was a significant and independent prognosticator of improved overall survival (HR = 0.84; 95 % CI 0.71-0.98). Many breast tumours express THRα2 at high levels and these patients experience improved survival. Thyroid hormone signalling may be important in a proportion of breast cancers and THRα2 expression may be a regulator of signalling in this pathway.

Multiple functional effects of RET kinase domain sequence variants in Hirschsprung disease.

The REarranged during Transfection (RET) gene encodes a receptor tyrosine kinase required for maturation of the enteric nervous system. RET sequence variants occur in the congenital abnormality Hirschsprung disease (HSCR), characterized by absence of ganglia in the intestinal tract. Although HSCR-RET variants are predicted to inactivate RET, the molecular mechanisms of these events are not well characterized. Using structure-based models of RET, we predicted the molecular consequences of 23 HSCR-associated missense variants and how they lead to receptor dysfunction. We validated our predictions in biochemical and cell-based assays to explore mutational effects on RET protein functions. We found a minority of HSCR-RET variants abrogated RET kinase function, while the remaining mutants were phosphorylated and transduced intracellular signals. HSCR-RET sequence variants also impacted on maturation, stability, and degradation of RET proteins. We showed that each variant conferred a unique combination of effects that together impaired RET protein activity. However, all tested variants impaired RET-mediated cellular functions, including cell transformation and migration. Our data indicate that the molecular mechanisms of impaired RET function in HSCR are highly variable. Although a subset of variants cause loss of RET kinase activity and downstream signaling, enzymatic inactivation is not the sole mechanism at play in HSCR.

RET-mediated cell adhesion and migration require multiple integrin subunits.

CONTEXT: The RET receptor tyrosine kinase is an important mediator of several human diseases, most notably of neuroendocrine cancers. These diseases are characterized by aberrant cell migration, a process tightly regulated by integrins. OBJECTIVE: Our goals were to investigate the role of integrins in RET-mediated migration in two neoplastic cell models: the neural-derived cell line SH-SY5Y, and the papillary thyroid carcinoma cell line TPC-1. We also evaluated whether multiple integrin subunits have a role in RET-mediated cell migration. DESIGN: We evaluated the expression and activation of integrins in response to RET activation using standard cell adhesion and migration (wound-healing) assays. We examined focal adhesion formation, using integrin-paxillin coimmunoprecipitations and immunofluorescence, as an indicator of integrin activity. RESULTS: Our data indicate that ß1 integrin (ITGB1) is expressed in both SH-SY5Y and TPC-1 cell lines and that these cells adhere strongly to matrices preferentially associated with ITGB1. We showed that RET can activate ITGB1, and that RET-induced cell adhesion and migration require ITGB1. Furthermore, we showed that ß3 integrin (ITGB3) also plays a role in RET-mediated cell adhesion and migration in vitro and ITGB3 expression correlates with RET-mediated invasion in a mouse tumor xenograft model, suggesting that RET mediates the activity of multiple integrin subunits. CONCLUSIONS: Our data are the first to show that multiple integrin subunits contribute to cell adhesion and migration downstream of RET, suggesting that coordinated signaling through these pathways is important for cell interactions with the microenvironment during tumor invasion and progression.