Rank ectopic expression in the presence of Neu and MMTV oncogenes alters mammary epithelial cell populations and their tumorigenic potential.

Determination of the mammary epithelial cell that serves as the cell of origin for breast cancer is key to understand tumor heterogeneity and clinical management. In this study, we aimed to decipher whether Rank expression in the presence of PyMT and Neu oncogenes might affect the cell of origin of mammary gland tumors. We observed that Rank expression in PyMT+/- and Neu+/- mammary glands alters the basal and luminal mammary cell populations already in preneoplasic tissue, which may interfere with the tumor cell of origin restricting their tumorigenesis ability upon transplantation assays. In spite of this, Rank expression eventually promotes tumor aggressiveness once tumorigenesis is established.

RANK signaling increases after anti-HER2 therapy contributing to the emergence of resistance in HER2-positive breast cancer.

BACKGROUND: Around 15-20% of primary breast cancers are characterized by HER2 protein overexpression and/or HER2 gene amplification. Despite the successful development of anti-HER2 drugs, intrinsic and acquired resistance represents a major hurdle. This study was performed to analyze the RANK pathway contribution in HER2-positive breast cancer and anti-HER2 therapy resistance. METHODS: RANK and RANKL protein expression was assessed in samples from HER2-positive breast cancer patients resistant to anti-HER2 therapy and treatment-naive patients. RANK and RANKL gene expression was analyzed in paired samples from patients treated with neoadjuvant dual HER2-blockade (lapatinib and trastuzumab) from the SOLTI-1114 PAMELA trial. Additionally, HER2-positive breast cancer cell lines were used to modulate RANK expression and analyze in vitro the contribution of RANK signaling to anti-HER2 resistance and downstream signaling. RESULTS: RANK and RANKL proteins are more frequently detected in HER2-positive tumors that have acquired resistance to anti-HER2 therapies than in treatment-naive ones. RANK (but not RANKL) gene expression increased after dual anti-HER2 neoadjuvant therapy in the cohort from the SOLTI-1114 PAMELA trial. Results in HER2-positive breast cancer cell lines recapitulate the clinical observations, with increased RANK expression observed after short-term treatment with the HER2 inhibitor lapatinib or dual anti-HER2 therapy and in lapatinib-resistant cells. After RANKL stimulation, lapatinib-resistant cells show increased NF-κB activation compared to their sensitive counterparts, confirming the enhanced functionality of the RANK pathway in anti-HER2-resistant breast cancer. Overactivation of the RANK signaling pathway enhances ERK and NF-κB signaling and increases lapatinib resistance in different HER2-positive breast cancer cell lines, whereas RANK loss sensitizes lapatinib-resistant cells to the drug. Our results indicate that ErbB signaling is required for RANK/RANKL-driven activation of ERK in several HER2-positive cell lines. In contrast, lapatinib is not able to counteract the NF-κB activation elicited after RANKL treatment in RANK-overexpressing cells. Finally, we show that RANK binds to HER2 in breast cancer cells and that enhanced RANK pathway activation alters HER2 phosphorylation status. CONCLUSIONS: Our data support a physical and functional link between RANK and HER2 signaling in breast cancer and demonstrate that increased RANK signaling may contribute to the development of lapatinib resistance through NF-κB activation. Whether HER2-positive breast cancer patients with tumoral RANK expression might benefit from dual HER2 and RANK inhibition therapy remains to be elucidated.

European Network of Breast Development and Cancer turned 10 years: a growing family of mammary gland researchers.

The European Network for Breast Development and Cancer (ENBDC), a worldwide network ( http://www.enbdc.org/ ), celebrated its tenth anniversary with a fantastic meeting last March 15-17, 2018 in Weggis with 76 attendees.

Patient-derived xenograft (PDX) models in basic and translational breast cancer research.

Patient-derived xenograft (PDX) models of a growing spectrum of cancers are rapidly supplanting long-established traditional cell lines as preferred models for conducting basic and translational preclinical research. In breast cancer, to complement the now curated collection of approximately 45 long-established human breast cancer cell lines, a newly formed consortium of academic laboratories, currently from Europe, Australia, and North America, herein summarizes data on over 500 stably transplantable PDX models representing all three clinical subtypes of breast cancer (ER+, HER2+, and "Triple-negative" (TNBC)). Many of these models are well-characterized with respect to genomic, transcriptomic, and proteomic features, metastatic behavior, and treatment response to a variety of standard-of-care and experimental therapeutics. These stably transplantable PDX lines are generally available for dissemination to laboratories conducting translational research, and contact information for each collection is provided. This review summarizes current experiences related to PDX generation across participating groups, efforts to develop data standards for annotation and dissemination of patient clinical information that does not compromise patient privacy, efforts to develop complementary data standards for annotation of PDX characteristics and biology, and progress toward "credentialing" of PDX models as surrogates to represent individual patients for use in preclinical and co-clinical translational research. In addition, this review highlights important unresolved questions, as well as current limitations, that have hampered more efficient generation of PDX lines and more rapid adoption of PDX use in translational breast cancer research.

Rankl Impairs Lactogenic Differentiation Through Inhibition of the Prolactin/Stat5 Pathway at Midgestation.

Prolactin and progesterone both orchestrate the proliferation and differentiation of the mammary gland during gestation. Differentiation of milk secreting alveoli depends on the presence of prolactin receptor, the downstream Jak2-Stat5 pathway and the transcription factor Elf5. A strict regulation of Rank signaling is essential for the differentiation of the mammary gland and in particular for alveolar commitment. Impaired alveologenesis and lactation failure are observed in both, knockout and Rank overexpressing mice; however, the underlying molecular mechanism responsible for these phenotypes remains largely unknown. Using genome-wide expression analyses and functional studies, we show here that Rankl (RL) exposure leads to impaired secretory differentiation of alveolar cells not only in MMTV-RANK but also in wild-type (WT) mammary acini. Conversely, pharmacological blockage of Rank signaling at midgestation in WT mice leads to precocious and exacerbated lactogenesis. Mechanistically, RL negatively regulates Stat5 phosphorylation and Elf5 expression at the onset of lactogenesis. Continuous RL exposure leads to the expansion of basal and bipotent cells in WT and MMTV-RANK acini. Overall, we demonstrate that enhanced Rank signaling impairs secretory differentiation during pregnancy by inhibition of the prolactin/p-Stat5 pathway.

RANK ligand mediates progestin-induced mammary epithelial proliferation and carcinogenesis.

RANK ligand (RANKL), a TNF-related molecule, is essential for osteoclast formation, function and survival through interaction with its receptor RANK. Mammary glands of RANK- and RANKL-deficient mice develop normally during sexual maturation, but fail to form lobuloalveolar structures during pregnancy because of defective proliferation and increased apoptosis of mammary epithelium. It has been shown that RANKL is responsible for the major proliferative response of mouse mammary epithelium to progesterone during mammary lactational morphogenesis, and in mouse models, manipulated to induce activation of the RANK/RANKL pathway in the absence of strict hormonal control, inappropriate mammary proliferation is observed. However, there is no evidence so far of a functional contribution of RANKL to tumorigenesis. Here we show that RANK and RANKL are expressed within normal, pre-malignant and neoplastic mammary epithelium, and using complementary gain-of-function (mouse mammary tumour virus (MMTV)-RANK transgenic mice) and loss-of function (pharmacological inhibition of RANKL) approaches, define a direct contribution of this pathway in mammary tumorigenesis. Accelerated pre-neoplasias and increased mammary tumour formation were observed in MMTV-RANK transgenic mice after multiparity or treatment with carcinogen and hormone (progesterone). Reciprocally, selective pharmacological inhibition of RANKL attenuated mammary tumour development not only in hormone- and carcinogen-treated MMTV-RANK and wild-type mice, but also in the MMTV-neu transgenic spontaneous tumour model. The reduction in tumorigenesis upon RANKL inhibition was preceded by a reduction in pre-neoplasias as well as rapid and sustained reductions in hormone- and carcinogen-induced mammary epithelial proliferation and cyclin D1 levels. Collectively, our results indicate that RANKL inhibition is acting directly on hormone-induced mammary epithelium at early stages in tumorigenesis, and the permissive contribution of progesterone to increased mammary cancer incidence is due to RANKL-dependent proliferative changes in the mammary epithelium. The current study highlights a potential role for RANKL inhibition in the management of proliferative breast disease.

APRIL promotes breast tumor growth and metastasis and is associated with aggressive basal breast cancer.

APRIL (a proliferation-inducing ligand) is a cytokine of the tumor necrosis factor family associated mainly with hematologic malignancies. APRIL is also overexpressed in breast carcinoma tissue lesions, although neither its role in breast tumorigenesis nor the underlying molecular mechanism is known. Here, we show that several breast cancer cell lines express APRIL and both its receptors, B cell maturation antigen (BCMA) and transmembrane activator and CAML-interactor (TACI), independently of luminal or basal tumor cell phenotype, and that the mitogen-activated protein kinases p38, ERK1/2, and JNK1/2 are activated in response to APRIL. The inflammatory stimulus poly I:C, a toll-like receptor (TLR) 3 ligand, enhanced APRIL secretion. Silencing experiments decreased cell proliferation, demonstrating that APRIL is a critical autocrine factor for breast tumor growth. Studies of 4T1 orthotopic breast tumors in APRIL transgenic mice showed that an APRIL-enriched environment increased tumor growth and promoted lung metastasis associated with enhanced tumor cell proliferation; BCMA and TACI expression suggests that both participate in these processes. We detected APRIL, BCMA and TACI in human luminal, triple-negative breast carcinomas and HER2 breast carcinomas, with increased levels in more aggressive basal tumors. APRIL was observed near Ki67(+) nuclei and was distributed heterogeneously in the cancer cells, in the leukocyte infiltrate, and in the myoepithelial layer adjacent to the tumor area; these results imply that APRIL provides proliferation signals to tumor cells through paracrine and autocrine signaling. Our study identifies participation of APRIL signaling in breast cancer promotion; we propose impairment of this pathway as a potential therapeutic strategy.

Constitutive activation of RANK disrupts mammary cell fate leading to tumorigenesis.

Receptor Activator of NF-kappa B (RANK) pathway controls mammary gland development in mice but its role in mammary stem cell fate remains undefined. We show that constitutive RANK signaling expands luminal and basal mammary compartments including mammary stem and luminal progenitor cell pools and interferes with the generation of CD61+ and Sca1+ luminal cells and Elf5 expression. Impaired mammary cell commitment upon RANK overexpression leads to the accumulation of progenitors including K14+K8+ bipotent cells and the formation of heterogeneous tumors containing hyperplastic basal, luminal, and progenitor cells. RANK expression increases in wild-type mammary epithelia with age and parity, and spontaneous preneoplastic lesions express RANK and accumulate K14+K8+ cells. In human breast tumors, high RANK expression levels are also associated with altered mammary differentiation. These results suggest that increased RANK signaling interferes with mammary cell commitment, contributing to breast carcinogenesis.

Cancer cell plasticity defines response to immunotherapy in cutaneous squamous cell carcinoma.

Immune checkpoint blockade (ICB) approaches have changed the therapeutic landscape for many tumor types. However, half of cutaneous squamous cell carcinoma (cSCC) patients remain unresponsive or develop resistance. Here, we show that, during cSCC progression in male mice, cancer cells acquire epithelial/mesenchymal plasticity and change their immune checkpoint (IC) ligand profile according to their features, dictating the IC pathways involved in immune evasion. Epithelial cancer cells, through the PD-1/PD-L1 pathway, and mesenchymal cancer cells, through the CTLA-4/CD80 and TIGIT/CD155 pathways, differentially block antitumor immune responses and determine the response to ICB therapies. Accordingly, the anti-PD-L1/TIGIT combination is the most effective strategy for blocking the growth of cSCCs that contain both epithelial and mesenchymal cancer cells. The expression of E-cadherin/Vimentin/CD80/CD155 proteins in cSCC, HNSCC and melanoma patient samples predicts response to anti-PD-1/PD-L1 therapy. Collectively, our findings indicate that the selection of ICB therapies should take into account the epithelial/mesenchymal features of cancer cells.

Identification of NOG as a specific breast cancer bone metastasis-supporting gene.

Metastasis requires numerous biological functions that jointly provide tumor cells from a primary site to seed and colonize a distant organ. Some of these activities are selected for in the primary site, whereas others are acquired at the metastatic niche. We provide molecular evidence showing that the BMP inhibitor, NOG, provides metastatic breast cancer cells with the ability to colonize the bone. NOG expression is acquired during the late events of metastasis, once cells have departed from the primary site, because it is not enriched in primary tumors with high risk of bone relapse. On the contrary, breast cancer bone metastatic lesions do select for high levels of NOG expression when compared with metastasis to the lung, liver, and brain. Pivotal to the bone colonization functions is the contribution of NOG to metastatic autonomous and nonautonomous cell functions. Using genetic approaches, we show that when NOG is expressed in human breast cancer cells, it facilitates bone colonization by fostering osteoclast differentiation and bone degradation and also contributes to metastatic lesions reinitiation. These findings reveal how aggressive cancer cell autonomous and nonautonomous functions can be mechanistically coupled to greater bone metastatic potential.

Luminal Rank loss decreases cell fitness leading to basal cell bipotency in parous mammary glands.

Rank signaling pathway regulates mammary gland homeostasis and epithelial cell differentiation. Although Rank receptor is expressed by basal cells and luminal progenitors, its role in each individual cell lineage remains unclear. By combining temporal/lineage specific Rank genetic deletion with lineage tracing techniques, we found that loss of luminal Rank reduces the luminal progenitor pool and leads to aberrant alveolar-like differentiation with high protein translation capacity in virgin mammary glands. These Rank-deleted luminal cells are unable to expand during the first pregnancy, leading to lactation failure and impairment of protein synthesis potential in the parous stage. The unfit parous Rank-deleted luminal cells in the alveoli are progressively replaced by Rank-proficient cells early during the second pregnancy, thereby restoring lactation. Transcriptomic analysis and functional assays point to the awakening of basal bipotency after pregnancy by the induction of Rank/NF-κB signaling in basal parous cell to restore lactation and tissue homeostasis.

RANK is a poor prognosis marker and a therapeutic target in ER-negative postmenopausal breast cancer.

Despite strong preclinical data, the therapeutic benefit of the RANKL inhibitor, denosumab, in breast cancer patients, beyond the bone, is unclear. Aiming to select patients who may benefit from denosumab, we hereby analyzed RANK and RANKL protein expression in more than 2,000 breast tumors (777 estrogen receptor-negative, ER- ) from four independent cohorts. RANK protein expression was more frequent in ER- tumors, where it associated with poor outcome and poor response to chemotherapy. In ER- breast cancer patient-derived orthoxenografts (PDXs), RANKL inhibition reduced tumor cell proliferation and stemness, regulated tumor immunity and metabolism, and improved response to chemotherapy. Intriguingly, tumor RANK protein expression associated with poor prognosis in postmenopausal breast cancer patients, activation of NFKB signaling, and modulation of immune and metabolic pathways, suggesting that RANK signaling increases after menopause. Our results demonstrate that RANK protein expression is an independent biomarker of poor prognosis in postmenopausal and ER- breast cancer patients and support the therapeutic benefit of RANK pathway inhibitors, such as denosumab, in breast cancer patients with RANK+ ER- tumors after menopause.

Evidence for a link between TNFRSF11A and risk of breast cancer.

Intracellular signaling mediated by the receptor activator of nuclear factor-κB [Rank, encoded by the tumor necrosis factor receptor superfamily, member 11a (Tnfrsf11a) gene] is fundamental for mammary gland development in mice, regulating the expansion of stem and progenitor cell compartments. Conversely, Rank overexpression in mice promotes abnormal proliferation and impairs differentiation, leading to an increased incidence of tumorigenesis. Here, we show that a common genetic variant near the 5'-end of TNFRSF11A, rs7226991, is associated with breast cancer risk in the general population and among carriers of mutations in the breast cancer 2, early onset (BRCA2) gene. Akin to the results of the Cancer and Genetics Markers of Susceptibility initiative, combined analysis of rs7226991 in two Spanish case-control studies (1,365 controls and 1,323 cases in total) revealed a significant association with risk: odds ratio (OR) = 0.88, 95% confidence interval (CI) 0.78-0.98, P (trend) = 0.025. Subsequent examination of BRCA1 (n = 1,017) and BRCA2 (n = 885) mutation carriers revealed a consistent association in the latter group: weighted hazard ratio ((w)HR) = 0.70; 95% CI 0.55-0.88; and P (trend) = 0.003; compared to BRCA1 mutation carriers, (w)HR = 0.91; 95% CI 0.76-1.10; and P (trend) = 0.33. The results of this study need to be replicated in other populations and with larger numbers of BRCA1/2 mutation carriers.

FGFR Inhibition Overcomes Resistance to EGFR-targeted Therapy in Epithelial-like Cutaneous Carcinoma.

PURPOSE: Recurrent and/or metastatic unresectable cutaneous squamous cell carcinomas (cSCCs) are treated with chemotherapy or radiotherapy, but have poor clinical responses. A limited response (up to 45% of cases) to EGFR-targeted therapies was observed in clinical trials with patients with advanced and metastatic cSCC. Here, we analyze the molecular traits underlying the response to EGFR inhibitors, and the mechanisms responsible for cSCC resistance to EGFR-targeted therapy. EXPERIMENTAL DESIGN: We generated primary cell cultures and patient cSCC-derived xenografts (cSCC-PDXs) that recapitulate the histopathologic and molecular features of patient tumors. Response to gefitinib treatment was tested and gefitinib-resistant (GefR) cSCC-PDXs were developed. RNA sequence analysis was performed in matched untreated and GefR cSCC-PDXs to determine the mechanisms driving gefitinib resistance. RESULTS: cSCCs conserving epithelial traits exhibited strong activation of EGFR signaling, which promoted tumor cell proliferation, in contrast to mesenchymal-like cSCCs. Gefitinib treatment strongly blocked epithelial-like cSCC-PDX growth in the absence of EGFR and RAS mutations, whereas tumors carrying the E545K PIK3CA-activating mutation were resistant to treatment. A subset of initially responding tumors acquired resistance after long-term treatment, which was induced by the bypass from EGFR to FGFR signaling to allow tumor cell proliferation and survival upon gefitinib treatment. Pharmacologic inhibition of FGFR signaling overcame resistance to EGFR inhibitor, even in PIK3CA-mutated tumors. CONCLUSIONS: EGFR-targeted therapy may be appropriate for treating many epithelial-like cSCCs without PIK3CA-activating mutations. Combined EGFR- and FGFR-targeted therapy may be used to treat cSCCs that show intrinsic or acquired resistance to EGFR inhibitors.

RANK links senescence to stemness in the mammary epithelia, delaying tumor onset but increasing tumor aggressiveness.

Rank signaling enhances stemness in mouse and human mammary epithelial cells (MECs) and mediates mammary tumor initiation. Mammary tumors initiated by oncogenes or carcinogen exposure display high levels of Rank and Rank pathway inhibitors have emerged as a new strategy for breast cancer prevention and treatment. Here, we show that ectopic Rank expression in the mammary epithelia unexpectedly delays tumor onset and reduces tumor incidence in the oncogene-driven Neu and PyMT models. Mechanistically, we have found that ectopic expression of Rank or exposure to Rankl induces senescence, even in the absence of other oncogenic mutations. Rank leads to DNA damage and senescence through p16/p19. Moreover, RANK-induced senescence is essential for Rank-driven stemness, and although initially translates into delayed tumor growth, eventually promotes tumor progression and metastasis. We uncover a dual role for Rank in the mammary epithelia: Rank induces senescence and stemness, delaying tumor initiation but increasing tumor aggressiveness.

RANK overexpression in transgenic mice with mouse mammary tumor virus promoter-controlled RANK increases proliferation and impairs alveolar differentiation in the mammary epithelia and disrupts lumen formation in cultured epithelial acini.

RANK and RANKL, the key regulators of osteoclast differentiation and activation, also play an important role in the control of proliferation and differentiation of mammary epithelial cells during pregnancy. Here, we show that RANK protein expression is strictly regulated in a spatial and temporal manner during mammary gland development. RANK overexpression under the control of the mouse mammary tumor virus (MMTV) promoter in a transgenic mouse model results in increased mammary epithelial cell proliferation during pregnancy, impaired differentiation of lobulo-alveolar structures, decreased expression of the milk proteins beta-casein and whey acidic protein, and deficient lactation. We also show that treatment of three-dimensional in vitro cultures of primary mammary cells from MMTV-RANK mice with RANKL results in increased proliferation and decreased apoptosis in the luminal area, resulting in bigger acini with filled lumens. Taken together, these results suggest that signaling through RANK not only promotes proliferation but also inhibits the terminal differentiation of mammary epithelial cells. Moreover, the increased proliferation and survival observed in a three-dimensional culture system suggests a role for aberrant RANK signaling during breast tumorigenesis.

Inhibition of RANK signaling in breast cancer induces an anti-tumor immune response orchestrated by CD8+ T cells.

Most breast cancers exhibit low immune infiltration and are unresponsive to immunotherapy. We hypothesized that inhibition of the receptor activator of nuclear factor-κB (RANK) signaling pathway may enhance immune activation. Here we report that loss of RANK signaling in mouse tumor cells increases leukocytes, lymphocytes, and CD8+ T cells, and reduces macrophage and neutrophil infiltration. CD8+ T cells mediate the attenuated tumor phenotype observed upon RANK loss, whereas neutrophils, supported by RANK-expressing tumor cells, induce immunosuppression. RANKL inhibition increases the anti-tumor effect of immunotherapies in breast cancer through a tumor cell mediated effect. Comparably, pre-operative single-agent denosumab in premenopausal early-stage breast cancer patients from the Phase-II D-BEYOND clinical trial (NCT01864798) is well tolerated, inhibits RANK pathway and increases tumor infiltrating lymphocytes and CD8+ T cells. Higher RANK signaling activation in tumors and serum RANKL levels at baseline predict these immune-modulatory effects. No changes in tumor cell proliferation (primary endpoint) or other secondary endpoints are observed. Overall, our preclinical and clinical findings reveal that tumor cells exploit RANK pathway as a mechanism to evade immune surveillance and support the use of RANK pathway inhibitors to prime luminal breast cancer for immunotherapy.

Management of bone health in solid tumours: From bisphosphonates to a monoclonal antibody.

Patients with solid tumours are at risk of impaired bone health from metastases and cancer therapy-induced bone loss (CTIBL). We review medical management of bone health in patients with solid tumours over the past 30 years, from first-generation bisphosphonates to the receptor activator of nuclear factor κB ligand (RANKL)-targeted monoclonal antibody, denosumab. In the 1980s, first-generation bisphosphonates were shown to reduce the incidence of skeletal-related events (SREs) in patients with breast cancer. Subsequently, more potent second- and third-generation bisphosphonates were developed, particularly zoledronic acid (ZA). Head-to-head studies showed that ZA was significantly more effective than pamidronate for reducing SREs in patients with breast and castrate-resistant prostate cancer (CRPC), becoming the standard of care for more than a decade. The RANKL inhibitor denosumab was licensed in 2010, and head-to-head studies and integrated analyses confirmed its superiority to ZA for preventing SREs, particularly in breast cancer and CRPC. Bisphosphonates and denosumab have also been investigated for prevention of CTIBL in patients receiving hormonal therapy for breast and prostate cancer, and denosumab is licensed in this indication. Despite advances in management of bone health, several issues remain, notably the optimal time to initiate therapy, duration of therapy, and dosing frequency, and how to avoid toxicity, particularly with long-term treatment. In summary, introduction of ZA and denosumab has protected patients with bone metastasis from serious bone complications and improved their quality of life. Ongoing research will hopefully guide the optimal use of these agents to help maintain bone health in patients with solid tumours.

PDGFR-induced autocrine SDF-1 signaling in cancer cells promotes metastasis in advanced skin carcinoma.

Advanced and undifferentiated skin squamous cell carcinomas (SCCs) exhibit aggressive growth and enhanced metastasis capability, which is associated in mice with an expansion of the cancer stem-like cell (CSC) population and with changes in the regulatory mechanisms that control the proliferation and invasion of these cells. Indeed, autocrine activation of PDGFRα induces CSC invasion and promotes distant metastasis in advanced SCCs. However, the mechanisms involved in this process were unclear. Here, we show that CSCs of mouse advanced SCCs (L-CSCs) express CXCR4 and CXCR7, both receptors of SDF-1. PDGFRα signaling induces SDF-1 expression and secretion, and the autocrine activation of this pathway in L-CSCs. Autocrine SDF-1/CXCR4 signaling induces L-CSC proliferation and survival, and mediates PDGFRα-induced invasion, promoting in vivo lung metastasis. Validation of these findings in patient samples of skin SCCs shows a strong correlation between the expression of SDF1, PDGFRA, and PDGFRB, which is upregulated, along CXCR4 in tumor cells of advanced SCCs. Furthermore, PDGFR regulates SDF-1 expression and inhibition of SDF-1/CXCR4 and PDGFR pathways blocks distant metastasis of human PD/S-SCCs. Our results indicate that functional crosstalk between PDGFR/SDF-1 signaling regulates tumor cell invasion and metastasis in human and mouse advanced SCCs, and suggest that CXCR4 and/or PDGFR inhibitors could be used to block metastasis of these aggressive tumors.