Lymphangiogenesis and lymphatic metastasis in breast cancer

Lymphatic metastasis is the main prognostic factor for survival of patients with breast cancer and other epithelial malignancies. Mounting clinical and experimental data suggest that migration of tumor cells into the lymph nodes is greatly facilitated by lymphangiogenesis, a process that generates new lymphatic vessels from pre-existing lymphatics with the aid of circulating lymphatic endothelial progenitor cells. The key protein that induces lymphangiogenesis is vascular endothelial growth factor receptor-3 (VEGFR-3), which is activated by vascular endothelial growth factor-C and -D (VEGF-C and VEGF-D). These lymphangiogenic factors are commonly expressed in malignant, tumor-infiltrating and stromal cells, creating a favorable environment for generation of new lymphatic vessels. Clinical evidence demonstrates that increased lymphatic vessel density in and around tumors is associated with lymphatic metastasis and reduced patient survival. Recent evidence shows that breast cancers induce remodeling of the local lymphatic vessels and the regional lymphatic network in the sentinel and distal lymph nodes. These changes include an increase in number and diameter of tumor-draining lymphatic vessels. Consequently, lymph flow away from the tumor is increased, which significantly increases tumor cell metastasis to draining lymph nodes and may contribute to systemic spread. Collectively, recent advances in the biology of tumor-induced lymphangiogenesis suggest that chemical inhibitors of this process may be an attractive target for inhibiting tumor metastasis and cancer-related death. Nevertheless, this is a relatively new field of study and much remains to be established before the concept of tumor-induced lymphangiogenesis is accepted as a viable anti-metastatic target. This review summarizes the current concepts related to breast cancer lymphangiogenesis and lymphatic metastasis while highlighting controversies and unanswered questions.     

Inhibition of VEGFR-3 activation in tumor-draining lymph nodes suppresses the outgrowth of lymph node metastases in the MT-450 syngeneic rat breast cancer model

For many types of human cancer, the expression of vascular endothelial growth factor-C (VEGF-C) correlates with enhanced tumor-associated lymphatic vessel density, metastasis formation and poor prognosis. In experimental animals, VEGF-C produced by primary tumors can induce lymphangiogenesis within and/or at the periphery of the tumor, and promotes metastasis formation. Tumor-induced lymphangiogenesis is therefore thought to expedite entry of tumor cells into the lymphatic vasculature and their trafficking to regional lymph nodes, thereby fostering metastatic dissemination. Tumour-produced VEGF-C can also drain to the regional lymph nodes and induce lymphangiogenesis there. Whether this activity promotes metastasis formation remains unclear. To address this issue we manipulated VEGF-C activity and VEGFR-3 activation in the lymph nodes draining syngeneic rat breast cancers using intra-dermal delivery of either recombinant VEGF-C or VEGFR-3 blocking antibodies to induce or suppress lymph node lymphangiogenesis, respectively. Recombinant VEGF-C induced lymph node lymphangiogenesis, but was not sufficient to promote metastasis formation by poorly metastatic NM-081 breast tumours. Conversely, inhibition of lymph node lymphangiogeneis induced by highly metastatic MT-450 breast tumours suppressed the outgrowth of lymph node metastases, but not the initial colonization of the lymph nodes. Lung metastasis was also not affected. We conclude that tumor-derived VEGF-C draining to regional lymph nodes promotes the outgrowth of lymph node metastases. VEGF-C may induce lung metastasis independently of its effects on lymph node metastasis.     

Overexpression of TrkB promotes the progression of colon cancer

Yu Y, Zhang S, Wang X, Yang Z, Ou G. Overexpression of TrkB promotes the progression of colon cancer. APMIS 2010; 118: 188–95. Studies have confirmed that TrkB plays important roles in facilitating metastasis in various types of malignant tumors. In the present study, 30 cases of colon cancer and matched non‐tumors were examined for the expression of TrkB by Western blot. The expression of TrkB was also examined in 90 colon tumor sections by immunohistochemical methods, and D2‐40 staining was used to evaluate the correlation between TrkB expression and lymphatic vessel density. To investigate the effects of TrkB on the progression of colon cancer, siRNA specific for TrkB was transfected into LoVo cells, and proliferation, apoptosis and invasion of trasfected cells were examined using MTT [3‐(4,5‐Dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide], flow cytometry and Transwell assays, respectively. Our results showed that TrkB was up‐regulated in colon tumors compared with the non‐tumorous counterparts, and the overexpression of TrkB was closely correlated with lymphatic vessel density (LVD) and metastasis. Inhibition of TrkB by siRNA increased the apoptotic rates of transfected cells, while the numbers of proliferative and invasive cells were decreased. In summary, our data suggest that overexpression of TrkB in colon cancer possibly plays roles in inhibiting apoptosis, promoting proliferation and invasion, facilitating tumor progression by lymphangiogenesis‐associated metastasis.     

Expression of vascular endothelial growth factor-C and its receptor in invasive micropapillary carcinoma of the breast

Invasion to lymphatic vessels and metastasis to lymph nodes are frequent complications in invasive micropapillary carcinoma (IMPC) of human breast cancer. Vascular endothelial growth factor-C (VEGF-C) and its receptor, VEGFR-3 have been implicated as the important factors in the formation of lymphatic vessels and recent experimental evidence strongly suggests that lymphangiogenesis in tumor promotes lymphatic metastasis. To clarify the mechanism of its occurrence, the expression of VEGF-C, VEGFR-3 and lymphatic vessel density (LVD) was examined in 40 cases of IMPC (pure and mixed type) and in 40 cases of pseudo-IMPC. Cytoplasmic expression of VEGF-C and VEGFR-3 were more frequent in tumor cells of IMPC compared to those of pseudo-IMPC. A significant positive correlation was found between the expression of VEGF-C and VEGFR-3 in both IMPC and pseudo-IMPC. The expression of VEGF-C was also significantly associated with higher peritumoral LVD, lymphatic invasion and number of lymph node metastasis in IMPC. These findings suggest that VEGF-C promotes the proliferation of peritumoral lymphatic vessels and that lymphatic invasion and metastasis to lymph nodes are frequently induced in IMPC of breast.     

Mammary cancer gene therapy targeting lymphangiogenesis: VEGF-C siRNA and soluble VEGF receptor-2, a splicing variant

Metastasis contributes significantly to cancer mortality, and the most common pathway of initial dissemination is via the afferent ducts of the lymphatics. Overexpression of vascular endothelial growth factor (VEGF)-C has been associated with lymphangiogenesis and lymph node metastasis in a multitude of human neoplasms, including breast cancers. We recently reported that both VEGF-C siRNA and endogenous soluble vascular endothelial growth factor receptor-2 (esVEGFR-2, a new splicing variant) inhibit VEGF-C function and metastasis in a mouse model of metastatic mammary cancer. Here we briefly review our previous experimental work, specifically targeting tumor lymphangiogenesis, in which metastatic mouse mammary cancers received direct intratumoral injections of either expression vectors VEGF-C siRNA or esVEGFR-2, or the empty plasmid vector, once a week for 6 or 8 weeks, followed by in vivo gene electrotransfer of the injected tumors. Throughout our study, both tumor lymphangiogenesis and the multiplicity of lymph node metastasis were significantly inhibited, with an overall reduction in tumor growth, by both VEGF-C siRNA and esVEGFR-2; further, a significant reduction in the number of dilated lymphatic vessels containing intraluminal cancer cells was observed with both treatments. Thus, therapeutic strategies targeting lymphangiogenesis may have great clinical significance for the treatment of metastatic human breast cancer.     

Biomaterial guides for lymphatic endothelial cell alignment and migration

Axillary dissection during breast cancer surgery produces extensive lymphatic vessel damage that often leads to lifelong secondary lymphedema of the arm. We have developed a biodegradable material conduit for lymphatic vessel reconstruction where fibers electrospun along the conduit lumen promote endothelial cell alignment and migration in vitro. The diameter and density of the electrospun fibers were optimized for cell migration and direction on two-dimensional substrates by seeding human lymphatic endothelial cells (LECs) onto aligned fibers of varying diameters and densities, randomly oriented fibers, and film substrates with no fibers. We found that LECs became aligned in the fiber direction, with cells seeded on the randomly oriented fibers becoming oriented in random directions, whereas cells seeded on the highly aligned fibers became highly aligned. Cell migration was dependent upon fiber alignment and density, with optimal migration found on 1300 nm diameter aligned fibers of low density. Blood endothelial cells seeded on the fibers exhibited similar behavior as the LECs. Fiber alignment was preserved upon rolling the two-dimensional substrate into the tubular geometry of a lymphatic vessel. The data suggest that aligned electrospun fibers may promote endothelial migration across the conduit in a manner that is independent of lymphatic growth factors.     

Tumor and lymph node lymphangiogenesis--impact on cancer metastasis

The extent of lymph node (LN) metastasis is a major determinant for the staging and the prognosis of most human malignancies and often guides therapeutic decisions. Although the clinical significance of LN involvement is well documented, little has been known about the molecular mechanisms that promote tumor spread via lymphatic vessels to sentinel and distal LN and beyond. However, recent discoveries have identified novel lymphatic-specific markers, and the newly discovered lymphangiogenesis factors vascular endothelial growth factor-C (VEGF-C) and VEGF-D were found to promote tumor-associated lymphatic vessel growth in mouse tumor models, leading to enhanced tumor spread to sentinel LN. Our recent findings indicate that VEGF-A also acts as a potent tumor lymphangiogenesis factor that promotes lymphatic tumor spread. VEGF-A overexpressing primary tumors induced sentinel LN lymphangiogenesis even before metastasizing and maintained their lymphangiogenic activity after metastasis to draining LN. Our recent studies showed that primary human melanomas that later metastasized were characterized by increased lymphangiogenesis and that the degree of tumor lymphangiogenesis can serve as a novel predictor of LN metastasis and overall patient survival, independently of tumor thickness. Tumor lymphangiogenesis also significantly predicted the presence of sentinel LN metastases at the time of surgical excision of the primary melanoma. Together, these findings suggest that tumor lymphangiogenesis actively contributes to cancer dissemination, that blockade of lymphatic vessel growth might inhibit tumor metastasis to LN, and that the extent of tumor-associated lymphangiogenesis could serve as a novel, prognostic parameter for the metastatic risk of human cancers.     

VEGF-C在淋巴管生成及乳腺癌淋巴道转移中的作用

目的： 探讨阻断VEGF-C/Flt-4调控系统对淋巴管生成和乳腺癌淋巴道转移的影响。方法： 体外培养胎牛胸导管内皮细胞，观察VEGF-C和抗Flt-4抗体对淋巴管内皮细胞增殖的影响；设计合成VEGF-C反义脱氧寡核苷酸（ASODN），体外实验观察其对VEGF-C基因表达的影响；建立乳腺癌裸鼠原位移植瘤模型并观察ASODN对肿瘤淋巴管生成及肿瘤生长转移的影响。结果： 加入前列腺癌细胞PC3(高表达VEGF-C)上清后，淋巴管内皮细胞增殖活跃；加入抗Flt-4抗体后各时段细胞计数均明显少于其它各组。体外实验RT-PCR及 Western blotting显示ASODN作用的MCF-7细胞组VEGF-C mRNA及蛋白表达均低于对照组。体内RT-PCR检测表明ASODN组移植瘤VEGF-C mRNA表达明显受抑制；5-Nase-ALPase双重酶组织化学法结果显示ASODN组移植瘤的淋巴管生成明显减少；ASODN组肿瘤生长速度较对照组缓慢，且肿瘤体积、淋巴结转移明显低于对照组。结论： VEGF-C/Flt-4调控系统与乳腺癌组织的淋巴管生成及肿瘤的淋巴道转移密切相关。阻断淋巴管内皮细胞Flt-4表达，可在一定程度上抑制肿瘤细胞诱导的淋巴管内皮细胞增殖；ASODN通过下调乳腺癌VEGF-C的表达，减少肿瘤淋巴管的生成及淋巴结转移。     

The biological significance of lymphangiogenesis in human tumours

Increasing evidence indicates that lymphangiogenesis in cancer is an important factor in promoting tumour progression and metastasis. The discovery of immunohistochemical markers for lymphatic vessels' identification as well as the characterization of lymphatic-specific growth factors and receptors afforded insight into the mechanisms involved in new lymphatic vessel formation and the process of lymphatic-borne metastasis. Quantitative assessment of lymphangiogenesis in malignant tumours has emerged as a promising prognostic indicator, although there are conflicting results on the impact of lymphatic vessel density to predict lymph nodal metastases and overall survival. Solid tumours were recently found to induce new lymphatic vessel growth in draining lymph nodes before the onset of metastasis and therefore lymphangiogenesis in the lymph nodes has gained great interest. This review highlights advances in our understanding of the mechanisms by which lymphangiogenesis in tumours and lymph nodes enhances metastases and reports the potential implications of these developments in cancer therapeutics.     

金黄地鼠舌癌发生过程中增殖性细胞核抗原的表达及淋巴管密度和面积与淋巴道转移的相关性

目的 通过观察金黄生鼠舌癌发生过程中增殖细胞核抗原(PCNA)的表达情况,分析淋巴管密度和面积的变化与舌癌恶性程度及淋巴道转移的相关性,探讨淋巴管生成与淋巴道转移的关系。 方法 用1.%丙烯酰胺-N,N-二甲基-N-丁基-N-甲基丙烯酸乙酯溴化铵(DMBA)丙酮溶液合并创伤方法,诱导金黄地鼠舌癌模型42只,每2周取材7只。采用HE染色确定舌癌的病理变化,PCNA和桥粒斑蛋白(Desmoplakin)免疫组织化学双标记法显示淋巴管增生情况,并测量肿瘤和淋巴管内皮细胞增殖指数(PI)、淋巴管密度(LVD)和淋巴管面积(LVA)作统计学分析。 结果 金黄地鼠舌癌的形成经历了非典型增生原位癌早期浸润癌的过程;在非典型增生组PI(91.55),LVA(7570.23),LVD(2.50);原位癌组PI(113.36), LVA(12105.45),LVD(3.73);早期浸润癌组PI(124.67),LVA(14524.33),LVD(5.33),各组间LVA,LVD,PI差异显著（P＜0.05）,且PI与LVA及LVD呈正相关(P＜0.05);淋巴结转移组PI(130.50),LVA(15430.67),LVD(6.17),非转移组PI(113.00),LVA(12711.67), LVD(3.67),两组差异显著（P＜0.05）。 结论 舌癌发生过程中存在新生淋巴管,舌癌形成过程中微淋巴管的LVA和LVD值增大,与舌癌的恶性程度呈正相关,与淋巴道转移呈正相关。     

Inducible nitric oxide synthase expression correlates with angiogenesis, lymphangiogenesis, and poor prognosis in gastric cancer patients

Increased nitric oxide synthase expression plays a key role in tumor progression. To examine inducible nitric oxide synthase expression and its correlation with clinical variables, such as tumor progression, angiogenesis, lymphangiogenesis, and prognosis in gastric cancer, we studied inducible nitric oxide synthase expression in gastric cancer samples from 211 patients with 5-year follow-up. CD105 and D2-40 were adopted as biomarkers for tumor angiogenesis and lymphangiogenesis, respectively. Inducible nitric oxide synthase staining was mainly found in the cytoplasm of gastric cancer tumor cells. Positive inducible nitric oxide synthase immunoreactivity was seen in 54.03% of gastric cancer specimens, which was correlated with lymph node metastasis, vascular invasion, distant metastasis, and TNM stage. Compared with inducible nitric oxide synthase negative patients, inducible nitric oxide synthase-positive patients had significantly shorter survival times and higher microvessel density and lymphatic vessel density. Intratumor and peritumor blood microvessel density and lymphatic vessel density correlated with inducible nitric oxide synthase expression (Spearman ρ test, P < .05). We conclude that inducible nitric oxide synthase expression correlates with lymph node metastasis, vascular invasion, distant metastasis, TNM stage, and poor survival rate in gastric cancer. We propose that synthesized inducible nitric oxide synthase increases angiogenesis, and lymphangiogenesis thus promotes tumor progression. Inducible nitric oxide synthase expression may be a good biomarker for poor prognosis in gastric cancer.     

Lateral peritumoral lymphatic vessel invasion can predict lymph node metastasis in esophageal squamous cell carcinoma.

Lymph node metastasis is an important prognostic factor in many types of cancer. We investigated the clinical significance of lymphangiogenesis and lymphatic vessel invasion in esophageal squamous cell carcinoma. We evaluated lymphatic vessel density and lymphatic vessel invasion in the intratumoral, peritumoral and normal compartments using D2-40 immunostaining. In addition, the peritumoral compartment was divided into the lateral peritumoral compartment and the non-lateral peritumoral compartment. The lymphatic vessel density was higher in the peritumoral and intratumoral compartments than in the normal compartment. However, the lymphatic vessel density did not correlate with any pathological parameters including lymph node metastasis. Intratumoral and peritumoral lymph vessels were small and collapsed while normal lymphatic vessels and lymphatic vessels with lymphatic vessel invasion were dilated and large. The presence of lymphatic vessel invasion, in the lateral peritumoral compartment but nowhere else, significantly correlated with lymph node metastasis. These results suggest that lymphangiogenesis might occur with esophageal cancer, but it does not play a direct role in lymphatic vessel invasion and lymph node metastasis. Peritumoral lymphatic vessel invasion, especially in the lateral peritumoral compartment, should imply a high probability of regional lymph node metastasis.     

Targeting COX-2 and EP4 to control tumor growth, angiogenesis, lymphangiogenesis and metastasis to the lungs and lymph nodes in a breast cancer model

We reported that cyclo-oxygenase (COX)-2 expression in human breast cancer stimulated cancer cell migration and invasiveness, production of vascular endothelial growth factor (VEGF)-C and lymphangiogenesis in situ, largely from endogenous PGE2-mediated stimulation of prostaglandin E (EP)1 and EP4 receptors, presenting them as candidate therapeutic targets against lymphatic metastasis. As human breast cancer xenografts in immuno-compromised mice have limitations for preclinical testing, we developed a syngeneic murine breast cancer model of spontaneous lymphatic metastasis mimicking human and applied it for mechanistic and therapeutic studies. We tested the roles of COX-2 and EP receptors in VEGF-C and -D production by a highly metastatic COX-2 expressing murine breast cancer cell line C3L5. These cells expressed all EP receptors and produced VEGF-C and -D, both inhibited with COX-2 inhibitors or EP4 (but not EP1, EP2 or EP3) antagonists. C3H/HeJ mice, when implanted SC in both inguinal regions with C3L5 cells suspended in growth factor-reduced Matrigel, exhibited rapid tumor growth, tumor-associated angiogenesis and lymphangiogenesis (respectively measured with CD31 and LYVE-1 immunostaining), metastasis to the inguinal and axillary lymph nodes and the lungs. Chronic oral administration of COX-1/COX-2 inhibitor indomethacin, COX-2 inhibitor celecoxib and an EP4 antagonist ONO-AE3-208, but not an EP1 antagonist ONO-8713 at nontoxic doses markedly reduced tumor growth, lymphangiogenesis, angiogenesis, and metastasis to lymph nodes and lungs. Residual tumors in responding mice revealed reduced VEGF-C and -D proteins, AkT phosphorylation and increased apoptotic/proliferative cell ratios consistent with blockade of EP4 signaling. We suggest that EP4 antagonists deserve clinical testing for chemo-intervention of lymphatic metastasis in human breast cancer.     

血管内皮生长因子C及其受体3在非小细胞肺癌组织中的表达及意义

目的　探讨血管内皮生长因子C(VEGF C)和受体 (VEGFR) 3在人非小细胞肺癌(NSCLC)组织中的表达及其与微血管、微淋巴管形成、淋巴转移、预后之间的关系。方法　对 76例人NSCLC及相应癌旁组织行VEGF C、VEGFR 3及CD34免疫组织化学染色链霉素抗生物素蛋白 过氧化物酶 (SP)法检测 ,进行淋巴管密度计数、微血管密度 (MVD)计数 ,并结合临床和病理资料进行分析。结果　NSCLC中 ,VEGF C的表达与肺癌分化程度负相关 (P =0 0 0 9)。VEGF C和VEGFR 3的表达水平与淋巴结转移呈正相关 (分别P =0 0 0 8,P =0 0 13) ,与淋巴浸润呈正相关 (分别P =0 0 2 7,P =0 0 2 0 )。VEGF C的表达与VEGFR 3在肺癌细胞中的表达呈正相关 (P =0 0 0 9)。VEGF C与淋巴管密度 (P =0 0 0 6 )、MVD(P =0 0 4 6 )呈正相关。淋巴管密度与淋巴结转移 (P =0 0 10 )、淋巴浸润 (P =0 0 19)、TNM分期 (P =0 0 15 )呈正相关 ,MVD与血行转移 (P <0 0 0 1)、TNM分期 (P <0 0 0 1)呈正相关。VEGF C阳性表达与生存时间、5年生存率呈负相关 (P <0 0 0 1)。结论　NSCLC中 ,VEGF C通过自分泌方式作用于受体VEGFR 3,促进肺癌组织生长 ,抑制分化。VEGF C促使肺癌内淋巴管形成 ,促进肺癌淋巴结转移。VEGF C和VEGFR 3表达增高、淋巴管密度增加     

Importance of lymph vessels in gastric cancer: a prognostic indicator in general and a predictor for lymph node metastasis in early stage cancer

BACKGROUND: Metastasis to regional lymph nodes (LNs) through lymphatic vessels is common in cancer progression and is an important prognostic factor in many cancers. Recent evidence suggests that tumour lymphangiogenesis promotes lymphatic metastasis. AIMS: To study the role of lymph vessel density (LVD) in gastric cancer and investigate whether LVD is associated with LN metastasis/prognosis. METHODS: Lymphatics of 117 primary human gastric cancer cases were investigated by quantitative immunohistochemical staining for podoplanin. The relation between LVD and LN metastasis and other established clinicopathological parameters was analysed. The relation between LVD and prognosis was also studied. RESULTS: Mean LVD of "hot spots" was 11.6/case. LVD significantly correlated with LN and podoplanin positive lymphatic invasion. High LVD was associated with worse overall survival. In multivariate analysis, positive LVD was a significant independent predictor of overall survival, depth of invasion, and TNM stage. LVD significantly correlated with LN metastasis at surgery and podoplanin positive lymphatic invasion. In multivariate analysis, positive LVD was an independent significant predictor of LN metastasis. CONCLUSIONS: Increased podoplanin expression is significantly associated with LN metastasis, and may play an important role in detecting LN metastasis in gastric cancer. Furthermore, LVD may be a significant prognostic factor in gastric cancer at any stage. In addition, LVD and lymph vessel invasion detected by podoplanin immunohistochemistry are associated with LN metastasis in T1 early gastric cancer. LVD assessment by podoplanin immunohistochemistry may become a useful predictor of LN metastasis in T1 early gastric cancer and may influence the decision making process for additional surgery.     

Inflammation-induced lymph node lymphangiogenesis is reversible

The extent of lymph node metastasis is a prognostic indicator of disease progression in many malignancies. Current noninvasive imaging technologies for the clinical assessment of lymph node metastases are based on the detection of cancer cells and commonly suffer from a lack of sensitivity. Recent evidence has indicated that the expansion of lymphatic networks (ie, lymphangiogenesis) within tumor-draining lymph nodes might be the earliest sign of metastasis. Therefore, we recently developed a noninvasive imaging method to visualize lymph node lymphangiogenesis in mice using radiolabeled antibodies against the lymphatic vessel endothelial hyaluronan receptor-1 (LYVE-1) as well as positron emission tomography (PET). This technique, termed anti-LYVE-1 immuno-PET, was found to be very sensitive in the detection of metastasis to the lymph nodes. However, lymphatic vessel expansion to the lymph nodes can also be induced by inflammation, and it is currently unclear whether such vessel expansion is reversed once inflammation has resolved. Detection of residual inflammation-induced lymph node lymphangiogenesis, thus, might hamper the identification of metastasized lymph nodes. In this study, we therefore used a well-established mouse model of inflammation in the skin to investigate whether lymphatic vessels in the lymph nodes regress on resolution of inflammation. Our data reveal that the lymphatic network indeed regresses on the resolution of inflammation and that we can image this process by anti-LYVE-1 immuno-PET.     

Mechanisms of lymphatic metastasis in human colorectal adenocarcinoma

The invasion of lymphatic vessels by colorectal cancer (CRC) and its subsequent spread to draining lymph nodes is a key determinant of prognosis in this common and frequently fatal malignancy. Although tumoural lymphangiogenesis is assumed to contribute to this process, review of the current literature fails to support any notion of a simple correlation between lymphatic vessel density and CRC metastasis. Furthermore, attempts to correlate the expression of various lymphangiogenic growth factors, most notably VEGF‐C and VEGF‐D, with the lymphatic metastasis of CRC have provided contradictory results. Recent evidence from animal and human models of tumour metastasis suggests that complex functional and biochemical interactions between the microvasculature of tumours and other cell types within the tumour microenvironment may play a pivotal role in the behaviour of commonly metastasizing tumours. Indeed, previous insights into tumoural blood vessels have provided candidate markers of tumoural angiogenesis that are currently the subject of intense investigation as future therapeutic targets. In this review article we survey the current evidence relating lymphangiogenesis and lymphangiogenic growth factor production to metastasis by CRC, and attempt to provide some insight into the apparent discrepancies within the literature. In particular, we also discuss some new and provocative insights into the properties of tumoural lymphatics suggesting that they have specific expression profiles distinct from those of normal lymphatic vessels and that appear to promote metastasis. These findings raise the exciting prospect of future biomarkers of lymphatic metastasis and identify potential targets for new generation anti‐tumour therapies. Copyright © 2009 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.