Discordance in ERα, PR and HER2 receptor status across different distant breast cancer metastases within the same patient

BACKGROUND

We studied discordance in estrogen receptor alpha (ERα), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) status between multiple distant metastases from the same breast cancer patient.

MATERIAL AND METHODS

Multiple distant metastases from 55 female patients were stained for ERα, PR and HER2 by immunohistochemistry and in situ hybridization for confirmation of the HER2 status.

RESULTS

Different metastatic sites within the same patient showed discordance in ERα receptor status in 7.3% or 10.9% of patients (using a 10% or 1% threshold for positivity, respectively). For PR, 29.1% or 30.9% of patients showed discordance. Taking ERα and PR together, 36.4% of cases (both thresholds) showed discrepancy between metastases. In 10.9% (10% threshold) or 14.5% of patients (1% threshold), such discordance could have clinical consequences with regard to hormonal treatment. For HER2, there was 3.6% discordance on the immunohistochemical level but 0% on the gene level.

CONCLUSION

In a significant proportion of metastatic breast cancer patients, discordance in ERα and PR receptor status between different metastatic sites was observed. This implies that multiple metastases may need to be biopsied to optimally reassess receptors.

Abstract P2-06-02: Genomic evolution from primary breast cancers to distant metastases

Purpose: Genomic evolution is an accepted concept during cancer development and progression. However, little is known about the changes that occur during the metastatic process despite the fact that breast cancer metastases are the leading cause of death in breast cancer patients. The purpose of this study was therefore to investigate whether distant breast cancer metastases show progression in copy number changes of onco- and tumor suppressor genes compared to their primary tumor.

Material and methods: Multiplex ligation-dependent probe amplification (MLPA) was used to compare copy number of 21 established oncogenes and tumor suppressor genes between primary breast cancer samples and corresponding distant metastases in 55 patients. Genes studied were ESR1, EGFR, FGFR1, ADAM 9, IKBKB, PRDM14, MTDH, MYC, CCND1, EMSY, CDH1, TRAF4, CPD, MED1, HER2, CDC6, TOP2A, MAPT, BIRC5, CCNE1 and AURKA.

Results: Overall, there was no significant difference in mean copy number between primary tumors (1.26 +/− 0.6) and metastases (1.27 +/− 0.64) (p = 0.826), but on the individual gene level, mean copy number for PRDM14 (p = 0,023), MED1 (p = 0.001) and CCNE1 (p = 0.039) were significantly higher while TRAF4 (p = 0.038) copy number was significantly lower in the metastases. Using dichotomized MLPA data, MTDH amplifications were significantly more frequent in the primary cancers compared to the metastases (27.3% vs.14.6%, p = 0.039), while significantly more CDH1 losses were found in the metastases compared to the primary tumor (23.6% vs. 9.1%, p = 0.039).

Conclusion: Distant breast cancer metastases show genomic evolution from the primary cancer as reflected by copy number changes in several established onco- and tumor suppressor genes.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P2-06-02.

Abstract P6-05-08: Significant heterogeneity in ERalpha and PR receptor status in different distant breast cancer metastases of the same patient

Purpose: Receptor conversion for estrogen receptor alpha (ERα), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) in single distant breast cancer metastases has been described before. However, most patients develop multiple metastases. Heterogeneity in receptor status between different metastases of the same patient has not been studied, probably since such material is very rare. The consequence of such heterogeneity would mean that as many metastases as possible need to be biopsied to re-assess receptor status.

We therefore aimed to study heterogeneity of receptor status between different distant metastases of the same patient in a relatively large group by re-staining all primary tumors and metastases with current optimal immunohistochemical methods on full sections.

Material and methods: Formalin fixed paraffin embedded tissue of primary breast carcinomas and corresponding multiple (≥2) distant metastases from 38 female patients were collected from several pathology departments in The Netherlands and stained for ERα, PR and HER2 by IHC. We evaluated the heterogeneity of receptor status between the metastases and the correlation with the primary tumor.

Results: In the 4 cases that showed ER conversion, 2 (50%) showed heterogeneity in receptor expression between different metastases of the same patient. Of the 17 cases that showed PR conversion, 12 cases (71%) showed heterogeneity in expression between metastases. There were no changes in the receptor profile of primary breast cancer to their metastases for HER2 in this group.

Conclusion: In a significant number of metastatic breast cancer patients, there is heterogeneity in ER and PR receptor status between different breast cancer metastases of the same patient. This implies that as many metastases as possible need to be biopsied to re-assess receptor status and set the optimal indication for hormonal therapy in these patients. Alternatively, non-invasive assessment of the receptor status by molecular imaging may be an easier future way to assess receptor status of all metastatic lesions.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P6-05-08.

Abstract P5-01-06: Differences in FGF1 and FGFR2 expression in BRCA1-associated, BRCA2-associated, and sporadic breast carcinomas

Introduction. In contrast to BRCA1-associated breast cancer, a distinctive phenotype for BRCA2-associated carcinomas has not been identified yet as there is no clear distinction between BRCA2- and non-BRCA mutation related or sporadic carcinomas. Recently, studies suggest overexpression of fibroblast growth factor 1 (FGF1) and fibroblast growth factor receptor 2 (FGFR2) in BRCA2 related cancers. The aim of the study was therefore to investigate whether there is differential expression of FGF1 and/or FGFR2 between BRCA2 related and sporadic and BRCA1 related cancers. This would reveal the usefulness of FGF1 and FGFR2 immunohistochemistry in daily pathology practise.

Method. Invasive breast carcinomas of 33 BRCA1 and 22 BRCA2 germline mutation carriers and a tissue microarray containing 104 sporadic invasive breast carcinomas were immunohistochemically stained for FGF1, FGFR2, estrogen receptor (ER), progesterone receptor (PR), HER2, epidermal growth factor receptor 1 (EGFR), cytokeratin (CK) 5/6 and CK14.

Results. FGFR2 expression was seen in 68.2% and 79.0% of BRCA2-associated and sporadic carcinomas respectively, in contrast to 22.6% of BRCA1-associated tumors (p = 0.000). FGF1 expression was seen in 72.7% of BRCA2-associated carcinomas and in 45.2% and 41.8% in BRCA1-associated and sporadic carcinomas, respectively (p = 0.032).

Conclusion. FGFR2 expression differs significantly between BRCA1- and BRCA2 associated breast carcinomas but not between BRCA2 and sporadic cancers. FGF1 expression differs significantly between BRCA2-associated and sporadic carcinomas and could be used as a BRCA2-specific biomarker.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P5-01-06.

Fibroblast growth factor receptors in breast cancer: expression, downstream effects, and possible drug targets

Cancer treatments are increasingly focusing on the molecular mechanisms underlying the oncogenic processes present in tumors of individual patients. Fibroblast growth factor receptors (FGFRs) are among the many molecules that are involved in oncogenesis and are currently under investigation for their potential as drug targets in breast cancer patients. These receptor tyrosine kinases play a role in several processes including proliferation, angiogenesis, and migration. Alterations in these basal processes can contribute to the development and progression of tumors. Among breast cancer patients, several subgroups have been shown to harbor genetic aberrations in FGFRs, including amplifications of FGFR1, FGFR2, and FGFR4 and mutations in FGFR2 and FGFR4. Here, we review in vitro and in vivo models that have partly elucidated the molecular implications of these different genetic aberrations, the resulting tumor characteristics, and the potential of FGFRs as therapeutic targets for breast cancer treatment.

Twist contributes to hormone resistance in breast cancer by downregulating estrogen receptor-α

The role of estrogen receptor-α (ER) in breast cancer development, and as a primary clinical marker for breast cancer prognosis, has been well documented. In this study, we identified the oncogenic protein, TWIST1 (Twist), which is overexpressed in high-grade breast cancers, as a potential negative regulator of ER expression. Functional characterization of ER regulation by Twist was performed using Twist low (MCF-7, T-47D) and Twist high (Hs 578T, MDA-MB-231, MCF-7/Twist) expressing cell lines. All Twist high expressing cell lines exhibited low ER transcript and protein levels. By chromatin immunoprecipitation and promoter assays, we demonstrated that Twist could directly bind to E-boxes in the ER promoter and significantly downregulate ER promoter activity in vitro. Functionally, Twist overexpression caused estrogen-independent proliferation of breast cells, and promoted hormone resistance to the selective estrogen receptor modulator tamoxifen and selective estrogen receptor down-regulator fulvestrant. Importantly, this effect was reversible on downregulating Twist. In addition, orthotopic tumors generated in mice using MCF-7/Twist cells were resistant to tamoxifen. These tumors had high vascular volume and permeability surface area, as determined by magnetic resonance imaging (MRI). Mechanistically, Twist recruited DNA methyltransferase 3B (DNMT3B) to the ER promoter, leading to a significantly higher degree of ER promoter methylation compared with parental cells. Furthermore, we demonstrated by co-immunoprecipitation that Twist interacted with histone deacetylase 1 (HDAC1) at the ER promoter, causing histone deacetylation and chromatin condensation, further reducing ER transcript levels. Functional re-expression of ER was achieved using the demethylating agent, 5-azacytidine, and the HDAC inhibitor, valproic acid. Finally, an inverse relationship was observed between Twist and ER expression in human breast tumors. In summary, the regulation of ER by Twist could be an underlying mechanism for the loss of ER activity observed in breast tumors, and may contribute to the generation of hormone-resistant, ER-negative breast cancer.

Lymphovascular Invasion in BRCA Related Breast Cancer Compared to Sporadic Controls

Background: Germline mutations in the BRCA1 and BRCA2 genes predispose to the development of breast cancer, exhibiting a specific histological phenotype. Identification of possible hallmarks of these tumours serves several purposes. Biomarkers can contribute to the selection of high-risk patients for genetic screening, help to identify the pathogenicity of so called “unclassified variant” mutations, and insight in the carcinogenetic pathways allows to develop new targeted therapies. Since BRCA1-associated breast cancers have pushing borders that prevent them from easily reaching vessels, and are often of the medullary (like) type that has a low rate of lymphovascular invasion (LVI), we hypothesized that absence of LVI could characterize BRCA1 related breast cancer.Methods: A population of 68 BRCA1 and 10 BRCA2 related invasive breast cancers was evaluated for LVI by an experienced breast pathologist blinded to mutation status, and compared to a control group matched for age, grade and tumour type.Results: LVI was present in 25.0% of BRCA1 related cases, compared to 20.6% of controls (P=0.54, OR=1.29, CI 0.58-2.78). No significant differences were found for the BRCA2 group either (P=1).Conclusion: LVI seems to occur as much in BRCA1 germline mutation related breast cancers as in sporadic controls. Apparently, these hereditary cancers find their way to the blood and lymph vessels despite their well demarcation and often medullary differentiation, indicating that these cancers may have specific vasculoinvasive properties.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 6019.

Molecular profile of ductal carcinoma in situ of the breast in BRCA1 and BRCA2 germline mutation carriers

Aims:

Ductal carcinoma in situ (DCIS) is an established late precursor of sporadic invasive breast cancer and to a large extent parallels its invasive counterpart with respect to molecular changes and immunophenotype. Invasive breast cancers in germline BRCA1 and BRCA2 mutation carriers have a distinct “basal” and “luminal” immunophenotype, respectively, but the immunophenotype of their precursor lesions has hardly been studied, and this was the aim of this study.

Methods:

DCIS lesions of 25 proven BRCA1 and 9 proven BRCA2 germline mutation carriers and their 22 and 6, respectively, accompanying invasive lesions were stained by immunohistochemistry for oestrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor (HER)2/neu, cytokeratin (CK)5/6, CK14, epidermal growth factor receptor (EGFR) and Ki67.

Results:

DCIS lesions in BRCA1 mutation carriers were mostly of the basal molecular type with low ER/PR/HER2 expression, while they frequently expressed CK5/6, CK14 and EGFR, and were mostly grade 3 and highly proliferative. DCIS lesions in BRCA2 mutation carriers were mostly of luminal molecular type with frequent expression of ER/PR, and infrequent expression of CK5/6, CK14 and EGFR, and they were mostly grade 3 and showed low proliferation. In BRCA1 and BRCA2 mutation carriers there was a high concordance between DCIS lesions and their concomitant invasive counterpart with regard to expression of individual markers as well as “molecular” subtype.

Conclusions:

Although the number of cases studied was low, DCIS lesions in BRCA1 and BRCA2 mutations carriers are usually of the basal and luminal molecular type, respectively, similar to their accompanying invasive cancers, thereby providing evidence that DCIS is a direct precursor lesion in these hereditary predisposed patients. This also suggests that crucial carcinogenetic events leading to these phenotypes in hereditary predisposed patients occur before the stage of invasion.

Progressive derailment of cell cycle regulators in endometrial carcinogenesis

BACKGROUND

Derailments of the control mechanisms of the cell cycle can initiate carcinogenesis, and play a role in progression to cancer.

AIM

To explore the expression of cell cycle proteins in normal, premalignant and malignant endometrial lesions representing the morphologically well defined stepwise model of human endometrial carcinogenesis

METHODS

Observational study. Paraffin-embedded specimens from inactive endometrium (n = 16), endometrial hyperplasia (n = 23) and endometrioid endometrial carcinoma (n = 39) were stained immunohistochemically for cyclin A, cyclin B1, cyclin D1, cyclin E, cdk2, p16, p21, p27, p53 and Ki67(MIB-1)). Differences in expression between the tissues, and correlation with classical prognostic factors for the carcinomas were analysed.

RESULTS

Expression of cyclin A and Ki67 gradually increased from normal through hyperplasia to carcinoma, indicating that proliferation increases over the carcinogenetic spectrum. cdk2, p16 and p21 gradually increased from normal through hyperplasia to carcinoma, indicating their potential importance in both early and late carcinogenesis. Cyclin D1, cyclin E and p53 especially increased and p27 decreased from hyperplasia to carcinoma, underlining their role in late carcinogenesis. In cancers, expression of cyclin A, p53 and Ki67 was positively correlated to grade, and cyclin A was positively correlated with cdk2, p21, Ki67, cyclin E and p53.

CONCLUSION

During (endometrioid) endometrial carcinogenesis, there is increasing proliferation paralleled by progressive derailment of cyclin B1, cyclin D1, cyclin E, p16, p21, p27, p53, and cdk2, indicating the importance of these cell cycle regulators in endometrial carcinogenesis.

Hypoxia-inducible factor-1alpha expression requires PI 3-kinase activity and correlates with Akt1 phosphorylation in invasive breast carcinomas

Hypoxia-inducible factor-1 alpha (HIF-1alpha) is the regulatory subunit of the heterodimeric transcription factor HIF-1 and the key factor in cellular response to low oxygen tension. Expression of HIF-1alpha protein is associated with poor patient survival and therapy resistance in many types of solid tumors. Insight into HIF-1alpha regulation in solid tumors is important for therapeutic strategies. In this study, we determined the pathophysiological relevance of HIF-1alpha regulation by the oncogenic phosphatidylinositol 3'-kinase (PI 3-kinase)/Akt signaling pathway. We modeled the physiology of hypoxic tumor regions by culturing carcinoma cells under low oxygen tension in the absence of serum. We observed that hypoxic induction of HIF-1alpha protein was decreased by serum deprivation. Overexpression of dominant-active Akt1 restored HIF-1alpha expression, whereas inhibition of PI 3-kinase activity reduced hypoxic HIF-1alpha protein levels to a similar extent as serum deprivation. Immunohistochemical analysis of 95 human breast cancers revealed that lack of Akt1 phosphorylation correlates with low HIF-1alpha levels. To our knowledge, this is the first reported comparison between HIF-1alpha expression and Akt phosphorylation in human carcinomas. We conclude that Akt activity is physiologically relevant for HIF-1alpha expression in breast cancer. This implies that HIF-1alpha function might be therapeutically targeted by inhibition of the PI 3-kinase/Akt pathway.

Distinction between hereditary and sporadic breast cancer on the basis of clinicopathological data

BACKGROUND

About 5% of all breast cancer cases are attributable to germline mutations in BRCA1 or BRCA2 genes. BRCA mutations in suspected carriers, however, may be missed, which hampers genetic counselling.

MATERIALS AND METHODS

Different clinicopathological features were compared between 22 breast cancers from carriers of proved BRCA1 mutations and 604 cancers from sporadic controls. In addition, 5 BRCA2-related breast cancers and 66 breast cancers of untested patients at intermediate risk and 19 breast cancers of untested patients at high risk of hereditary disease on the basis of family history were evaluated.

RESULTS

A "probably sporadic" class (age >or=54 years and epidermal growth factor receptor (EGFR) negative; 68% of cases) with a 0% chance of BRCA1-related breast cancer containing 79% of the sporadic cases was yielded by using a decision tree with age, Ki67 and EGFR. A 75% chance of BRCA1-related breast cancer was shown by the "probably BRCA1-related" class (age <54 years and Ki67 >or=25%; 8% of cases) with 82% of the BRCA1-related cases but only 1.4% of the sporadic cases. Most cases at intermediate or high risk of hereditary disease on the basis of family history could be classified with high probability as either probably BRCA1 related or probably sporadic.

CONCLUSION

Breast carcinomas can be classified with a high level of certainty as sporadic or related to BRCA1 germline mutations by using a decision tree with age, Ki67 and EGFR. This can be clinically useful in mutation analysis in families with a borderline risk of hereditary disease.

Interplay between VHL/HIF1α and Wnt/β-catenin pathways during colorectal tumorigenesis

Activation of the Wnt signaling pathway initiates the transformation of colorectal epithelial cells, although the transition to metastatic cancer requires angiogenesis. We have investigated the expression of the von Hippel-Lindau (VHL) tumor suppressor in the intestines from humans and mice. Here, we show that VHL expression is regulated by TCF4 and is restricted to the proliferative compartment at the bottom of intestinal crypts. Accordingly, VHL is completely absent from the proliferative intestinal pockets of Tcf4(-/-) perinatal mice. We observed complementary staining of the hypoxia-inducible factor (HIF) 1alpha to VHL in normal intestinal epithelium as well as in all stages of colorectal cancer (CRC). To the best of our knowledge, this is the first report demonstrating the presence of nuclear HIF1alpha in normoxic healthy adult tissue. Although we observed upregulated levels of VHL in very early CRC lesions from sporadic and familial adenomatous polyposis patients - presumably due to activated Wnt signaling - a clear reduction of VHL expression is observed in later stages of CRC progression, coinciding with stabilization of HIF1alpha. As loss of VHL in later stages of CRC progression results in stabilization of HIF, these data provide evidence that selection for VHL downregulation provides a proangiogenic impulse for CRC progression.

Up-regulation of gene expression by hypoxia is mediated predominantly by hypoxia-inducible factor 1 (HIF-1)

The hypoxia-inducible factor 1 (HIF-1) plays a critical role in cellular responses to hypoxia. The aim of the present study was to evaluate which genes are induced by hypoxia, and whether this induction is mediated by HIF-1, by expression microarray analysis of wt and HIF-1alpha null mouse fibroblasts. Forty-five genes were up-regulated by hypoxia and 40 (89%) of these were regulated by HIF-1. Of the 114 genes down-regulated by hypoxia, 19 (17%) were HIF-1-dependent. All glycolytic enzymes were strongly up-regulated by hypoxia in a HIF-1-dependent manner. Genes already known to be related to hypoxia, such as glucose transporter 1, BNIP3, and hypoxia-induced gene 1, were induced. In addition, multiple new HIF-1-regulated genes were identified, including genes involved in metabolism (adenylate kinase 4, galactokinase), apoptosis (galectin-3 and gelsolin), and invasion (RhoA). Genes down-regulated by hypoxia were involved in cytoskeleton maintenance (Rho kinase), mRNA processing (heterogeneous nuclear ribonucleoprotein H1 and splicing factor), and DNA repair (REV3). Furthermore, seven cDNAs from genes with unknown function or expressed sequence tags (ESTs) were up-regulated and 27 such cDNAs were down-regulated. In conclusion, hypoxia causes down- rather than up-regulation of gene expression and HIF-1 seems to play a major role in the regulation of hypoxia-induced genes.

Hypoxia-inducible factor-1alpha is associated with angiogenesis, and expression of bFGF, PDGF-BB, and EGFR in invasive breast cancer

AIMS

Hypoxia-inducible factor-1 (HIF-1) is the key transcription factor regulating the cellular response to hypoxia, including angiogenesis. Growth factors play an important role in tumour growth and angiogenesis and some have been shown to be induced by HIF-1 in vitro. This study investigated if angiogenesis or growth factors or their receptors are associated with HIF-1alpha in invasive breast cancer.

METHODS AND RESULTS

High levels of HIF-1alpha, detected by immunohistochemistry in 45 breast cancers, were positively associated with increased microvessel density (as a measure of angiogenesis) (P = 0.023). Furthermore, high levels of HIF-1alpha were associated with epithelial expression (> or = 10%) of epidermal growth factor receptor (EGFR) (P = 0.011), platelet-derived growth factor (PDGF)-BB (P < 0.001), and basic fibroblast growth factor (bFGF) (P = 0.045). A positive, yet insignificant, trend for HIF-1alpha to be associated with epithelial expression of transforming growth factor (TGF)-alpha (P = 0.081) and vascular endothelial growth factor (VEGF) (P = 0.109) was noticed as well as an inverse association with stromal expression of TGF-beta-R1 (P = 0.070).

CONCLUSIONS

In invasive breast cancer, HIF-1alpha is associated with angiogenesis, and expression of growth factors bFGF and PDGF-BB, and the receptor EGFR. Thus, agents targeting HIF-1 may combine different pathways of inhibiting breast cancer growth, including angiogenesis and growth factors.

Differential prognostic impact of hypoxia induced and diffuse HIF-1alpha expression in invasive breast cancer

BACKGROUND

Intratumorous hypoxia triggers a broad cellular response mediated by the transcription factor hypoxia inducible factor 1 (HIF-1). HIF-1alpha concentrations increase during breast carcinogenesis, and are associated with poor prognosis. An earlier study noted two HIF-1alpha overexpression patterns: diffuse scattered throughout the tissue and confined to perinecrotic cells.

AIMS

To investigate the prognostic impact of these different HIF-1alpha overexpression patterns in relation to its downstream effectors carbonic anhydrase (CA) IX and glucose transporter 1 (GLUT-1).

METHODS

HIF-1alpha, CA IX, and GLUT-1 expression was studied by immunohistochemistry, including double staining for CA IX and HIF-1alpha. Clinical data included disease free survival, lymph node status, and tumour size.

RESULTS

HIF-1alpha overexpression (44% of cases) had a perinecrotic (13.5%) or diffuse staining pattern (30.5%). CA IX expression was detectable in 12.5% of breast cancers, whereas GLUT-1 expression was seen in 29%, with both showing perinecrotic membrane staining. Perinecrotic HIF-1alpha overexpression was highly associated with CA IX and GLUT-1 overexpression, and double staining for HIF-1alpha and CA IX showed strong expression in the same cells. Diffusely overexpressed HIF-1alpha was not associated with CA IX or GLUT-1 expression. Patients with diffuse HIF-1alpha staining had a significantly better prognosis than patients with perinecrotically overexpressed HIF-1alpha.

CONCLUSIONS

Different regulation pathways of HIF-1alpha overexpression exist in breast cancer: (1) hypoxia induced, perinecrotic HIF-1alpha overexpression with strong expression of hypoxia associated genes (CA IX and GLUT-1), which is associated with a poor prognosis; and (2) diffuse HIF-1alpha overexpression lacking major hypoxia associated downstream effects, resulting in a more favourable prognosis.

Lack of lymphangiogenesis during breast carcinogenesis

BACKGROUND

Recent evidence suggests that functional intratumorous lymph vessels may be absent from some human cancers. This could result from either the failure of tumours to induce lymphangiogenesis, or the collapse of lymph vessels, caused by high interstitial tumour pressure.

METHODS

To differentiate between these two hypotheses, paraffin wax embedded clinical specimens from normal breast (n = 13), usual ductal hyperplasia (n = 11), ductal carcinoma in situ (n = 21), and invasive breast cancer (n = 40) were compared for lymphatic and blood vessel density by immunohistochemistry with antibodies to the lymphatic endothelial hyaluronan receptor (LYVE-1) and CD31, respectively.

RESULTS

Lymph vessel density was lower than blood vessel density in normal breast tissue. Within breast lobuli, lymph vessels were absent. In premalignant lesions blood microvessel density increased, whereas no increase in lymph vessels could be seen intralesionally. In invasive cancers, lymph vessels were absent in all but a few cases, where probably some pre-existing lymph vessels remained, although blood microvessel density was once again increased.

CONCLUSION

Unlike angiogenesis, lymphangiogenesis is absent during breast carcinogenesis. This, and not rising interstitial pressure caused by an increase in the size of lesions, explains the absence of intratumorous lymph vessels in invasive breast cancer.

Tissue distribution of the multidrug resistance protein

The human multidrug resistance protein (MRP) is a 190 kd membrane glycoprotein that can cause resistance of human tumor cells to various anticancer drugs, by extruding these drugs out of the cell. Three different monoclonal antibodies, directed against different domains of MRP, allowed us to determine the localization of MRP in a panel of normal human tissues and malignant tumors. Whereas in malignant tumors strong plasma membrane MRP staining was frequently observed, in normal human tissues MRP staining was predominantly cytoplasmatic. Here, MRP was detected in several types of epithelia, muscle cells, and macrophages. From the presence of MRP in many epithelia we infer that MRP, like MDR1 P-glycoprotein, may have an excretory function in protecting the organism against xenobiotics. Recent studies indicate a role for MRP as a carrier for transport of glutathione-conjugated endo- and xenobiotics. The presence of MRP in bronchiolar epithelium, heart muscle, and macrophages would agree with the glutathione S-conjugate carrier activity previously detected in these cells. Furthermore, in 46 of 119 untreated tumors from various histogenetic origins MRP staining was seen. In these tumors MRP may contribute to the intrinsic resistance against treatment with chemotherapeutic drugs.