Name: a modified in vitro invasion assay to determine the potential role of hormones, cytokines and/or growth factors in mediating cancer cell invasion
Uploaded: 2015-04-24T14:00:00
Description: Watch this Scientific Journal Video about A Modified In vitro Invasion Assay to Determine the Potential Role of Hormones, Cytokines and/or Growth Factors in Mediating Cancer Cell Invasion at JoVE.com

The authors acknowledge funding sources from D&#8217;Youville College School of Pharmacy, Buffalo, NY.

1. Prepare the Different Media and Additional Components
<ol>
	<li>Prior to experiment, prepare media consisting of DMEM or other specified media with the addition of either normal FBS, charcoal stripped FBS, or charcoal stripped FBS plus the component to be tested. Note that multiple components can be tested in each experiment.</li>
	<li>Weigh out and dilute the hormones, growth factors, or cytokines appropriately to be dissolved in the charcoal stripped serum at the physiological concentration.</li>
</ol>
<p class="j...

<ol>
	<li>Weinberg, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> The Biology of Cancer. , (2013).</li><li>Hanahan, D., Weinberg, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hallmarks+of+cancer:+the+next+generation.">Hallmarks of cancer: the next generation.</a> Cell. 144 (5), 646-674 (2011).</li><li>Hanahan, D., Weinberg, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+hallmarks+of+cancer.">The hallmarks of cancer.</a> Cell. 100 (1), 57-70 (2000).</li><li>Valastyan, S., Weinberg, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tumor+metastasis:+molecular+insights+and+evolving+paradigms.">Tumor metastasis: molecular insights and evolving paradigms.</a> Cell. 147 (2), 275-292 (2011).</li><li>Dang, Z. C., Lowik, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Removal+of+serum+factors+by+charcoal+treatment+promotes+adipogenesis+via+a+MAPK-dependent+pathway.">Removal of serum factors by charcoal treatment promotes adipogenesis via a MAPK-dependent pathway.</a> Mol Cell Biochem. 268 (1-2), 159-167 (2005).</li><li>Yohay, D. A., Zhang, J., Thrailkill, K. M., Arthur, J. M., Quarles, L. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+of+serum+in+the+developmental+expression+of+alkaline+phosphatase+in+MC3T3-E1+osteoblasts.">Role of serum in the developmental expression of alkaline phosphatase in MC3T3-E1 osteoblasts.</a> J Cell Physiol. 158 (3), 467-475 (1994).</li><li>Zucker, S. N., Bancroft, T. A., Place, D. E., Des Soye, ., Bagati, B., Berezney, A., R, <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+dominant+negative+Cx43+mutant+differentially+affects+tumorigenic+and+invasive+properties+in+human+metastatic+melanoma+cells.">A dominant negative Cx43 mutant differentially affects tumorigenic and invasive properties in human metastatic melanoma cells.</a> J Cell Physiol. 228 (4), 853-859 (2013).</li><li>Fox, E. M., Andrade, J., Shupnik, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Novel+actions+of+estrogen+to+promote+proliferation:+integration+of+cytoplasmic+and+nuclear+pathways.">Novel actions of estrogen to promote proliferation: integration of cytoplasmic and nuclear pathways.</a> Steroids. 74 (7), 622-627 (2009).</li><li>Meierjohann, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=MMP13+mediates+cell+cycle+progression+in+melanocytes+and+melanoma+cells:+in+vitro+studies+of+migration+and+proliferation.">MMP13 mediates cell cycle progression in melanocytes and melanoma cells: in vitro studies of migration and proliferation.</a> Molecular Cancer. 9, 201 (2010).</li><li>Smalley, K. S., Haass, N. K., Brafford, P. A., Lioni, M., Flaherty, K. T., Herlyn, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multiple+signaling+pathways+must+be+targeted+to+overcome+drug+resistance+in+cell+lines+derived+from+melanoma+metastases.">Multiple signaling pathways must be targeted to overcome drug resistance in cell lines derived from melanoma metastases.</a> Mol Cancer Ther. 5 (5), 1136-1144 (2006).</li><li>Both, N. J., Vermey, M., Dinjens, W. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+comparative+evaluation+of+various+invasion+assays+testing+colon+carcinoma+cell+lines.">A comparative evaluation of various invasion assays testing colon carcinoma cell lines.</a> Br J Cancer. 81 (6), 934-941 (1999).</li><li>Fidler, I. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+pathogenesis+of+cancer+metastasis:+the+'seed+and+soil'+hypothesis+revisited.">The pathogenesis of cancer metastasis: the 'seed and soil' hypothesis revisited.</a> Nat. Rev. Cancer. 3, 453-458 (2003).</li><li>Huang, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Epithelial+to+mesenchymal+transition+in+human+breast+epithelial+cells+transformed+by+17beta-estradiol.">Epithelial to mesenchymal transition in human breast epithelial cells transformed by 17beta-estradiol.</a> Cancer Res. 67 (23), 11147-11157 (2007).</li><li>Huang, Y. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thyroid+hormone+regulation+of+miR-21+enhances+migration+and+invasion+of+hepatoma.">Thyroid hormone regulation of miR-21 enhances migration and invasion of hepatoma.</a> Cancer Res. 73 (8), 2505-2517 (2013).</li><li>Scheel, C., Weinberg, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cancer+stem+cells+and+epithelial-mesenchymal+transition:+concepts+and+molecular+links.">Cancer stem cells and epithelial-mesenchymal transition: concepts and molecular links.</a> Semin. Cancer Biol. 22 (5-6), 396-403 (2012).</li><li>Kojima, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Autocrine+TGF-beta+and+stromal+cell-derived+factor-1+(SDF-1)+signaling+drives+the+evolution+of+tumor-promoting+mammary+stromal+myofibroblasts.Proc.">Autocrine TGF-beta and stromal cell-derived factor-1 (SDF-1) signaling drives the evolution of tumor-promoting mammary stromal myofibroblasts.Proc.</a> Natl Acad Sci U S A. 107 (46), 20009-20014 (2010).</li><li>Maehara, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+of+transforming+growth+factor-&#946;1+in+invasion+and+metastasis+in+gastric+carcinoma.">Role of transforming growth factor-&#946;1 in invasion and metastasis in gastric carcinoma.</a> J. Clin. Oncology. 17 (2), 607-614 (1999).</li><li>Lu, Z., Jiang, G., Blume-Jensen, P., Hunter, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Epidermal+growth+factor-induced+tumor+cell+invasion+and+metastasis+initiated+by+dephosphorylation+and+downregulation+of+focal+adhesion+kinase.">Epidermal growth factor-induced tumor cell invasion and metastasis initiated by dephosphorylation and downregulation of focal adhesion kinase.</a> Mol. Cell Biol. 21 (12), 4016-4031 (2001).</li><li>Korkaya, H., Liu, S., Wicha, M. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Breast+Cancer+stem+cells,+cytokine+networks,+and+the+tumor+microenvironment.">Breast Cancer stem cells, cytokine networks, and the tumor microenvironment.</a> J. Clin. Invest. 121 (10), 3804-3809 (2011).</li><li>Rosen, E. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+interrogation+of+HGF-SF+with+other+cytokines+in+tumor+invasion+and+metastasis.">The interrogation of HGF-SF with other cytokines in tumor invasion and metastasis.</a> EXS. 65, 301-310 (1993).</li><li>Sanz-Moreno, V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=ROCK+and+JAK1+signaling+cooperate+to+control+actomyosin+contractility+in+tumor+cells+and+stroma.">ROCK and JAK1 signaling cooperate to control actomyosin contractility in tumor cells and stroma.</a> Cancer Cell. 20 (2), 229-245 (2011).</li><li>Fleming, J. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Paracrine+interactions+between+primary+human+human+fibroblasts+enhance+murine+mammary+gland+humanization+in+vivo.">Paracrine interactions between primary human human fibroblasts enhance murine mammary gland humanization in vivo.</a> Breast Cancer Res. 14 (3), (2012).</li><li>Sikora, <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=M.J.,+V.,+M.E.,+M.D.,+J.M.">M.J., V., M.E., M.D., J.M.</a> Mechanisms of estrogen-independent breast cancer growth driven by low estrogen concentrations are unique versus complete estrogen deprivation.Breast Cancer Res Treat. 134 (3), 1027-1039 (2012).</li></ol>

Tumor metastasis is a multistep process. The cells must break through the basement membrane, intravasate into either the lymphatic system or blood microvessels, in which they are transported to distant sites. The tumor cells then extravasate and colonize into a macrometastasis12. Progression through the epithelial to mesenchymal transition (EMT), tumor invasion, and metastasis has been enhanced by steroid hormones13,14, growth factors15-18, and cytokines19-21. These molecules a...

A novel invasion assay has been developed with the goal of identifying the involvement of specific hormones, cytokines and/or growth factors as chemoattractants in cancer cell invasion. The ability of tumor cells to invade through the extracellular matrix (ECM) is a hallmark of the metastatic phenotype1-3. Invasion chambers have been extensively used as in vitro tools to study cancer cell invasion and migration and may provide knowledge as to the mechanisms of in vivo tumor invasion and metastasis. The chambers consist of cylindrical cell culture inserts nested within the wells of cell culture plates. The bottoms of the inserts are semi-permeable polycarbonate or polystyrene membranes of defined pore sizes.
In the standard invasion assay, cells are seeded onto the insert membrane with serum free media and placed into cell culture wells that are filled with serum or serum-like chemoattractants to set up a chemoattractive force. This force drives cells to move through the semi-permeable membrane (migration) or alternatively, through a coating of extracellular matrix (invasion), which can then be stained using conventional dyes to detect and quantify the number of cells. The cell number is then normalized according to the extent of migration and invasion in a noninvasive cell line. This method allows an investigator to evaluate the invasive potential of different cell types under a variety of conditions, including genetic manipulations.
Hormones, cytokines and growth factors are critical components of serum and are increasingly being shown to be associated with driving the invasive phenotype4. However, the nature, role, and specificity of these chemoattractive serum molecules in mediating invasion still remain elusive. The challenge remains to determine what specific factors in serum or serum-like chemoattractants are responsible for driving cancer cell invasion as well as what molecules may inhibit the invasion process. In this report, we describe a methodology to evaluate the potential involvement of hormones, cytokines and/or growth factors present in serum, as molecules driving the chemoattraction and invasion of cancer cells.
In this proposed modified protocol, charcoal stripping is used to remove hormones, cytokines and growth factors from 2% fetal bovine serum (FBS) to generate 2% charcoal stripped FBS (CS-FBS). Both 2% FBS and 2% CS-FBS are used as agents to set up the chemoattractive force to drive cancer cell invasion. Using 2% CS-FBS as a chemoattractive agent in comparison to normal 2% FBS affords several benefits including first, and most prominently, the ability to study the cancer invasion phenotype in the reduced/relative absence of hormones, cytokines and growth factors. It also enables the investigator to assess whether the collective removal of hormones, growth factors, and cytokines causes an increase or decrease in the invasive index. The assay is then designed to determine whether the addition of an individual component, designated as &#8220;X&#8221; can inhibit, decrease, increase, or restore the invasive index to its original value (see Figures 2 &#38; 3). Although this methodology is specific for achieving the physiological levels of the component that is removed from the serum during charcoal stripping, it should also be noted that charcoal stripping can also affect signal transduction pathways. For example, it has been reported that charcoal stripping can decrease the alkaline phosphatase activity of osteoprogenitor cells and induce adipogenesis through reduction of MAPK activators5. Charcoal stripped media are commercially available and are based on the protocol outlined that combines charcoal with dextran and incubated with fetal bovine serum O/N6.
This assay was developed in response to a result reported by Zucker et al.7 The authors demonstrated that a mutant phenotype affecting gap junction communication demonstrated an increase in the invasion index when migrating toward media with normal 2% FBS. This increase was eliminated with the substitution of charcoal-stripped serum. From this result, the authors concluded that this mutant affected migration toward a lipophilic molecule (more specifically, a hormone, growth factor, or cytokine)7. It is well known that hormones, growth factors, and cytokines mediate signaling pathways involved in tumor promotion and invasion4. Thus, it is important for scientific investigators to determine what factor(s) are driving the tumor invasion of their particular cancer cells or mutants under study. The assay is designed to address the role of individual components at their physiological concentration as determined according to the difference between the concentration of the component &#8220;X&#8221; in normal FBS and the CS-FBS. Through the development of this assay, investigators can gain more insight into the specific invasive pathway governing their system.
Hormones, growth factors, and cytokines have often been classified as tumor promoters8. Some of these factors such as EGF are used as direct sources for chemoattractants in invasion chambers9. Thus, it seems likely that these represent the major components of the serum that direct tumor invasion. This protocol proposes a simple, yet significant, modification to the conventional in vitro invasion assay which allows an investigator to assess the involvement of hormones, growth factors, and cytokines in mediating the invasive potential of cancer cells. However, the assay is designed to provide the investigator with an answer as to whether the procedure will be effective for their study at an early step in the analysis, so as not to use precious time and resources if deemed unnecessary. This method uses CS-FBS and relies on the investigators discretion as to which molecules to pursue as lead candidates that potentially mediate cancer cell invasion. The results from these analyses should prove to be useful in identifying which serum components serve as chemoattractants or inhibitors for the particular cell line or mutant being studied. In addition, this approach may help the investigator identify key signaling pathways either promoting or inhibiting cancer cell invasion; thus directing future drug design.

<table border="0" cellpadding="0" cellspacing="0" width="987">
	<tbody>
		<tr height="22">
			<td height="22" style="height:22px;width:367px;">Item</td>
			<td style="width:195px;">Vendor</td>
			<td style="width:136px;">Catalog #</td>
			<td style="width:289px;">Comments/Description</td>
		</tr>
		<tr height="42">
			<td>BioCoat Control Inserts with 8.0&#181;m PET Membrane 
			(12 in each of two 24-Well Plates)</td>
			<td>Corning</td>
			<td>354578</td>
			<td>polyethylene teraphthalate (PET) membranes&#160;&#160;</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;">Collagen I, rat tail</td>
			<td>Corning</td>
			<td>354236</td>
			<td>Source = rat tail tendon, purity = 90%</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;">Fixative; Diff-Quick</td>
			<td>Thermo Fisher Scientific</td>
			<td>NC9844047</td>
			<td>Methanol-based fixative, Hmatoxylin/Eosin</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;">Fetal bovine Serum</td>
			<td>Life Technologies</td>
			<td>16000</td>
			<td>Designated as FBS</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;">Charcoal Stripped Fetal Bovine Serum</td>
			<td>Life Technologies</td>
			<td>12676</td>
			<td>Designated as CS-FBS</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;">Fetal bovine Serum</td>
			<td>Thermo Scientific Hyclone</td>
			<td>SH30070</td>
			<td>Designated as FBS</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;">Charcoal Stripped Fetal Bovine Serum</td>
			<td>Thermo Scientific Hyclone</td>
			<td>SH30068</td>
			<td>Designated as CS-FBS</td>
		</tr>
	</tbody>
</table>

a modified in vitro invasion assay to determine the potential role of hormones, cytokines and/or growth factors in mediating cancer cell invasion

Blood serum serves as a chemoattractant towards which cancer cells migrate and invade, facilitating their intravasation into microvessels. However, the actual molecules towards which the cells migrate remain elusive. This modified invasion assay has been developed to identify targets which drive cell migration and invasion. This technique compares the invasion index under three conditions to determine whether a specific hormone, growth factor, or cytokine plays a role in mediating the invasive potential of a cancer cell. These conditions include i) normal fetal bovine serum (FBS), ii) charcoal-stripped FBS (CS-FBS), which removes hormones, growth factors, and cytokines and iii) CS-FBS + molecule (denoted &#8220;X&#8221;). A significant change in cell invasion with CS-FBS as compared to FBS, indicates the involvement of hormones, cytokines or growth factors in mediating the change. Individual molecules can then be added back to CS-FBS to assay their ability to reverse or rescue the invasion phenotype. Furthermore, two or more factors can be combined to evaluate the additive or synergistic effects of multiple molecules in driving or inhibiting invasion. Overall, this method enables the investigator to determine whether hormones, cytokines, and/or growth factors play a role in cell invasion by serving as chemoattractants or inhibitors of invasion for a particular type of cancer cell or a specific mutant. By identifying specific chemoattractants and inhibitors, this modified invasion assay may help to elucidate signaling pathways that direct cancer cell invasion.

The invasion index is calculated for each condition according to normalization to a noninvasive cell line. For our experiments, we use the 1205Lu melanoma cell line and established variant stable cell lines as our invasive lines as well as the premalignant noninvasive variant, WM793 from which the 1205Lu cells were derived10 which serves as a logical control. We also utilize collagen I as the invasion matrix because that is the primary component of the dermis. This is in accordance with a previous study whereb...

Watch this Scientific Journal Video about A Modified In vitro Invasion Assay to Determine the Potential Role of Hormones, Cytokines and/or Growth Factors in Mediating Cancer Cell Invasion at JoVE.com

A Modified In vitro Invasion Assay to Determine the Potential Role of Hormones, Cytokines and/or Growth Factors in Mediating Cancer Cell Invasion

This video article describes a modified in vitro method to examine the role of hormones, cytokines and/or growth factors in driving cancer cell invasion.

A Modified In vitro Invasion Assay to Determine the Potential Role of Hormones, Cytokines and/or Growth Factors in Mediating Cancer Cell Invasion

Blood serum serves as a chemoattractant towards which cancer cells migrate and invade, facilitating their intravasation into microvessels. However, the ...

Research

JoVE Journal

Medicine

A Real-time Electrical Impedance Based Technique to Measure Invasion of Endothelial Cell Monolayer by Cancer Cells

Metastatic dissemination of malignant cells requires degradation of basement membrane, attachment of tumor cells to vascular endothelium, retraction of ...

An In Vitro System to Study Tumor Dormancy and the Switch to Metastatic Growth

An In Vitro System to Study Tumor Dormancy and the Switch to Metastatic Growth

Recurrence of breast cancer often follows a long latent period in which there are no signs of cancer, and metastases may not become clinically apparent ...

Multi-photon Imaging of Tumor Cell Invasion in an Orthotopic Mouse Model of Oral Squamous Cell Carcinoma

Loco-regional invasion of head and neck cancer is linked to metastatic risk and presents a difficult challenge in designing and implementing patient ...

Spheroid Assay to Measure TGF-&#946;-induced Invasion

Spheroid Assay to Measure TGF-ÃƒÅ½Ã‚Â²-induced Invasion

TGF-&beta; has opposing roles in breast cancer progression by acting as a tumor suppressor in the initial phase, but stimulating invasion and metastasis ...

Modeling and Imaging 3-Dimensional Collective Cell Invasion

A defining characteristic of cancer malignancy is invasion and metastasis 1. In some cancers (e.g. glioma 2), local invasion into surrounding healthy ...

In vitro Mesothelial Clearance Assay that Models the Early Steps of Ovarian Cancer Metastasis

In vitro Mesothelial Clearance Assay that Models the Early Steps of Ovarian Cancer Metastasis

Ovarian cancer is the fifth leading cause of cancer related deaths in the United States1. Despite a positive initial response to therapies, 70 to 90 ...

Assessment of Ovarian Cancer Spheroid Attachment and Invasion of Mesothelial Cells in Real Time

Ovarian cancers metastasize by shedding into the peritoneal fluid and dispersing to distal sites within the peritoneum. Monolayer cultures do not ...

Focus Formation: A Cell-based Assay to Determine the Oncogenic Potential of a Gene

Malignant transformation of cells is typically associated with increased proliferation, loss of contact inhibition, acquisition of anchorage-independent ...

Establishment of a Human Multiple Myeloma Xenograft Model in the Chicken to Study Tumor Growth, Invasion and Angiogenesis

Multiple myeloma (MM), a malignant plasma cell disease, remains incurable and novel drugs are required to improve the prognosis of patients. Due to the ...

Three-Dimensional (3D) Tumor Spheroid Invasion Assay

Three-Dimensional 3D Tumor Spheroid Invasion Assay

Invasion of surrounding normal tissues is generally considered to be a key hallmark of malignant (as opposed to benign) tumors. For some cancers in ...