Prognostic impact of mRNA levels of osteopontin splice variants in soft tissue sarcoma patients

  • Antje Hahnel1Email author,

    Affiliated with

    • Henri Wichmann1Email author,

      Affiliated with

      • Thomas Greither2,

        Affiliated with

        • Matthias Kappler3,

          Affiliated with

          • Peter Würl4,

            Affiliated with

            • Matthias Kotzsch5,

              Affiliated with

              • Helge Taubert3, 6, 7,

                Affiliated with

                • Dirk Vordermark1 and

                  Affiliated with

                  • Matthias Bache1

                    Affiliated with

                    BMC Cancer201212:131

                    DOI: 10.1186/1471-2407-12-131

                    Received: 19 December 2011

                    Accepted: 2 April 2012

                    Published: 2 April 2012

                    Abstract

                    Background

                    It is well known that osteopontin (OPN) plays an important role in tumor progression and that a high OPN expression level in several tumor entities correlates with poor prognosis in cancer patients. However, little is known about the prognostic relevance of the OPN mRNA splice variants.

                    Methods

                    We analyzed the mRNA expression levels of different OPN splice variants in tumor tissue of 124 soft tissue sarcoma (STS) patients. Quantitative real-time PCR (qRT-PCR) was used to analyze the mRNA expression level of three OPN splice variants (OPN-a, -b and -c).

                    Results

                    The multivariate Cox's proportional hazard regression model revealed that high mRNA expression levels of OPN splice variants are significantly associated with poor prognosis in STS patients (n = 124). Women (n = 68) with high mRNA expression levels of OPN-a and OPN-b have an especially elevated risk of tumor-related death (OPN-a: RR = 3.0, P = 0.01, CI = 1.3-6.8; OPN-b: RR = 3.4, P = 0.01, CI = 1.4-8.2). In particular, we found that high mRNA expression levels of OPN-b and OPN-c correlated with a high risk of tumor-related death in STS patients that received radiotherapy (n = 52; OPN-b: RR = 10.3, P < 0.01, CI = 2.0-53.7; OPN-c: RR = 11.4, P < 0.01, CI = 2.2-59.3).

                    Conclusion

                    Our study shows that elevated mRNA expression levels of OPN splice variants are negative prognostic and predictive markers for STS patients. Further studies are needed to clarify the impact of the OPN splice variants on prognosis.

                    Background

                    Osteopontin is a secreted phosphoprotein that plays an important role in tumor progression. It affects processes such as cellular growth, cell migration, invasion, metastasis and decay of the extracellular matrix [1]. Several studies showed that an increased OPN expression correlates with poor prognosis in cancer patients [24]. However, only a few studies have analyzed the importance of OPN for tumor progression in sarcomas. OPN protein expression level was shown to be elevated in tumor cells, and high OPN levels were associated with high tumor stage, tumor grade and poor survival in sarcoma patients [57]. Additionally, Bramwell et al. (2005) showed that OPN mRNA is also overexpressed in the tumor tissue of STS patients. In a previous study, we demonstrated that higher OPN protein expression levels in tumor tissue and serum were associated with worse prognosis in STS patients [8].

                    Young et al. (1990) identified three splice variants of OPN, but their specific functions remained unclear. In addition to the full-length form osteopontin-a (OPN-a) with 7 exons, there are the splice variants osteopontin-b (OPN-b) and osteopontin-c (OPN-c) with deletions of exon 5 and exon 4, respectively. The first in vitro studies demonstrated a different impact of the OPN splice variants on cell migration, invasion, apoptosis and proliferation in various cancer cell lines [913]. Compared to normal tissue, the tumor tissues of different cancer entities express higher levels of OPN splice variants [10, 12, 1418]. However, only one study, which investigates breast cancer patients, analyzed the prognostic impact of the OPN splice variants [15]. In the present study, we analyzed the prognostic relevance of the expression level of the three OPN splice variants (OPN-a, -b and -c) in the tumor tissue of 124 STS patients.

                    Methods

                    Patients and tissue samples

                    We analyzed the frozen primary tumor samples of 124 STS patients and surrounding tissue of 15 STS patients by qRT-PCR for the mRNA expression of OPN splice variants (partially described in [8]). The clinical and histomorphological parameters of the STS patients are shown in Table 1. In total, 50.8% of STS patients (n = 63) were still alive after an average follow-up time of 57.3 (range 9-198) months, and 49.2% of STS patients (n = 61) died from tumor-related reasons after an average of 28.0 (range 2-201) months. The tumors were staged according to the Union for International Cancer Control (UICC) system. All patients gave their written informed consent to the Institute of Pathology, University of Halle, Germany, and Department of Surgery 1, University of Leipzig, Germany. The study was approved by the Ethics Committee of the Medical Faculty of the Martin-Luther-University Halle-Wittenberg and is in compliance with the Helsinki Declaration.
                    Table 1

                    Clinical and histomorphological data

                    Parameter

                    Total (n = 124)

                    OPN-a mRNA expression

                    OPN-b mRNA expression

                    OPN-c mRNA expression

                      

                    low (n = 62)

                    high (n = 62)

                    low (n = 62)

                    high (n = 62)

                    low (n = 62)

                    high (n = 62)

                    Sex

                     

                    P = 0.02

                    P = 0.10

                    P = 0.37

                       Male

                    56

                    35

                    21

                    33

                    23

                    31

                    25

                       Female

                    68

                    27

                    41

                    29

                    39

                    31

                    37

                    Histological subtype

                     

                    P = 0.96

                    P = 0.17

                    P = 0.17

                       Liposarcoma

                    27

                    14

                    13

                    14

                    13

                    13

                    14

                       MFH/Fibrosarcoma

                    38

                    17

                    21

                    14

                    24

                    14

                    24

                       NS

                    15

                    8

                    7

                    9

                    6

                    9

                    6

                       RMS + LMS

                    29

                    15

                    14

                    14

                    15

                    15

                    14

                       other STS

                    15

                    8

                    7

                    11

                    4

                    11

                    4

                    Tumor grade

                     

                    P = 0.03

                    P = 0.05

                    P = 0.03

                       I

                    16

                    6

                    10

                    6

                    10

                    4

                    12

                       II

                    70

                    42

                    28

                    42

                    28

                    42

                    28

                       III

                    37

                    13

                    24

                    14

                    23

                    16

                    21

                    Tumor stage

                     

                    P = 0.37

                    P = 0.43

                    P = 0.33

                       I

                    15

                    7

                    8

                    7

                    8

                    5

                    10

                       II

                    57

                    33

                    24

                    33

                    24

                    33

                    24

                       III

                    40

                    18

                    22

                    17

                    23

                    19

                    21

                       IV

                    12

                    4

                    8

                    5

                    7

                    5

                    7

                    Tumor localization

                     

                    P = 0.29

                    P = 0.26

                    P = 0.30

                       Extremities

                    79

                    37

                    42

                    37

                    42

                    36

                    43

                       Thorax

                    12

                    5

                    7

                    5

                    7

                    6

                    6

                       Head and neck

                    4

                    1

                    3

                    1

                    3

                    1

                    3

                       Abdominal

                    27

                    18

                    9

                    17

                    10

                    18

                    9

                       Other

                    2

                    1

                    1

                    2

                    0

                    1

                    1

                    Recurrence

                     

                    P = 1.00

                    P = 1.00

                    P = 1.00

                       Yes

                    55

                    28

                    27

                    28

                    27

                    27

                    28

                       No

                    69

                    34

                    35

                    34

                    35

                    35

                    34

                    Lymph node status

                     

                    P = 0.21

                    P = 0.21

                    P = 0.03

                       N0

                    118

                    61

                    57

                    61

                    57

                    62

                    56

                       N1

                    6

                    1

                    5

                    1

                    5

                    0

                    6

                    Distant metastases

                     

                    P = 0.28

                    P = 0.88

                    P = 0.88

                       M0

                    45

                    25

                    20

                    23

                    22

                    23

                    2

                       M1

                    50

                    20

                    30

                    24

                    26

                    24

                    26

                       Evaluation not possible

                    3

                    2

                    1

                    2

                    1

                    2

                    1

                    Radiation

                     

                    P = 1.00

                    P = 0.86

                    P = 0.86

                       Yes

                    58

                    29

                    29

                    30

                    28

                    30

                    28

                       No

                    66

                    33

                    33

                    32

                    34

                    32

                    34

                    Chemotherapy

                     

                    P = 0.74

                    P = 0.74

                    P = 0.74

                       Yes

                    10

                    4

                    6

                    4

                    6

                    4

                    6

                       No

                    114

                    58

                    56

                    58

                    56

                    58

                    56

                    Abbreviations: MFH - malignant fibrous histiocytoma, NS - neurogenic sarcoma, RMS - rhabdomyosarcoma, LMS - leiomyosarcoma

                    RNA preparation, cDNA synthesis and transcript analysis by quantitative real-time PCR (qRT-PCR)

                    The total RNA of the frozen tissue samples was isolated by the Trizol method (Invitrogen, Karlsruhe, Germany), and the cDNA was prepared using the RevertAid™ H Minus First Strand cDNA Synthesis Kit (Fermentas, St.Leon-Rot, Germany) according to the manufacturer's instructions. All qRT-PCR reactions were performed on a Rotorgene RG-6000 (LTF, Wasserburg, Germany) using the QuantiTect SYBRGreen PCR Kit (Fermentas). The primer sequences of the OPN splice variants and specific annealing temperatures are summarized in Table 2 (previously described in [14]). HPRT (hypoxanthine-guanine phosphoribosyltransferase) was used as a housekeeping gene (for standardization) and a marker for integrity of the cDNA. All methods were previously described in detail [8].
                    Table 2

                    Primers for quantitative real-time RT-PCR

                    Gene

                    Primer

                    Sequence 5' → 3'

                     

                    Localization

                    Annealing temperature

                    HPRT

                    HPRT309

                    5'-TTGCTGACCTGCTGGATTAC-3'

                    sense

                    391-410

                    58°C

                     

                    HPRT507

                    5'-CTTGCGACCTTGACCATCTT-3'

                    antisense

                    633-652

                     

                    OPN-a

                    OPN-a fw 323

                    5'-ATCTCCTAGCCCCACAGAAT-3'

                    sense

                    323-342

                    58°C

                     

                    OPN-a rev 508

                    5'-CATCAGACTGGTGAGAATCATC-3'

                    antisense

                    529-508

                     

                    OPN-b

                    OPN-b fw 323

                    5'-ATCTCCTAGCCCCACAGAC-3'

                    sense

                    323-341

                    62°C

                     

                    OPN-b rev 509

                    5'-AAAATCAGTGACCAGTTCATCAG-3'

                    antisense

                    531-509

                     

                    OPN-c

                    OPN-c fw 246

                    5'-TGAGGAAAAGCAGAATGCTG-3'

                    sense

                    246-265

                    58°C

                     

                    OPN-c rev 377

                    5'-GTCAATGGAGTCCTGGCTGT-3'

                    antisense

                    396-377

                     

                    Sequences and localization of primers used in this study correspond to mRNA sequences of HPRT [Genbank: NM_000194.2], OPN-a [Genbank: NM_001040058.1], OPN-b [Genbank: NM_000582.2] and OPN-c [Genbank: NM_001040060.1]

                    Statistical analysis

                    The statistical analysis was carried out using SPSS 17.0 (SPSS Inc., Chicago, IL, USA). Spearman's rho test was used for bivariate linear regression analyses. For survival analysis, the Kaplan-Meier method and the multivariate Cox's proportional hazard regression model were applied with appropriate adjustment to tumor type, tumor stage and tumor localization. We used a log-rank test to compare the survival curves of Kaplan-Meier analysis and to test for statistical differences. A two-tailed Fisher's exact-test or chi-square test was performed to determine the associations between mRNA expression level of OPN splice variants and different clinical parameters. A Wilcoxon signed-rank test was used to analyze the statistical differences of the 15 paired tumor and normal tissues. For survival analysis and comparison with clinical parameters, the cut-off values were set according to the median of mRNA expression levels of OPN splice variants (Table 3). A probability ≥ 95% (P ≤ 0.05) was considered an indicator of a significant difference between mean values.
                    Table 3

                    Kaplan-Meier analyses and multivariate Cox's regression analyses

                    STS patients

                    OPN splice variant

                    n

                    Median values

                    [copies OPN splice

                    variant mRNA/

                    copies HPRT mRNA]

                    Kaplan-Meier analysis

                    multivariate Cox's regression model

                        

                    Survival [months]

                    P

                    RR

                    P

                    CI

                    All

                    OPN-a low

                    62

                    0.68

                    90

                        
                     

                    OPN-a high

                    62

                     

                    71

                    1.7

                    1.7

                    0.06

                    1.0-3.0

                     

                    OPN-b low

                    62

                    0.49

                    117

                        
                     

                    OPN-b high

                    62

                     

                    66

                    0.13

                    2.1

                    0.02

                    1.2-3.6

                     

                    OPN-c low

                    62

                    0.08

                    94

                        
                     

                    OPN-c high

                    62

                     

                    81

                    0.38

                    1.8

                    0.04

                    1.0-3.1

                    Female

                    OPN-a low

                    34

                    0.83

                    116

                        
                     

                    OPN-a high

                    34

                     

                    53

                    0.08

                    3.0

                    0.01

                    1.3-6.8

                     

                    OPN-b low

                    34

                    0.58

                    102

                        
                     

                    OPN-b high

                    34

                     

                    42

                    0.13

                    3.4

                    < 0.01

                    1.4-8.2

                     

                    OPN-c low

                    34

                    0.09

                    92

                        
                     

                    OPN-c high

                    34

                     

                    46

                    0.50

                    2.3

                    0.07

                    0.9-5.4

                    RT patients

                    OPN-a low

                    26

                    0.65

                    80

                        
                     

                    OPN-a high

                    26

                     

                    76

                    0.04

                    3.5

                    0.07

                    0.9-13.0

                     

                    OPN-b low

                    26

                    0.42

                    147

                        
                     

                    OPN-b high

                    26

                     

                    55

                    0.05

                    10.3

                    < 0.01

                    2.0-53.7

                     

                    OPN-c low

                    26

                    0.07

                    147

                        
                     

                    OPN-c high

                    26

                     

                    55

                    0.05

                    11.4

                    < 0.01

                    2.2-59.3

                    Association of the mRNA expression of OPN splice variants in different groups of patients (all STS patients, females and RT patients) with overall survival. The median values of OPN-a, OPN-b and OPN-c were used as cut-off points to divide the STS patients into two groups: one with high and one with low (reference group) OPN mRNA levels in tumor tissues

                    Results and discussion

                    mRNA expression levels of OPN splice variants in STS tissues

                    The analysis of mRNA expression levels of OPN splice variants in the tumor tissues of 124 STS patients reveals a median transcript ratio of 0.68 copies OPN-a mRNA/copies HPRT mRNA (range: 9.30*10-4-85.29), 0.49 copies OPN-b mRNA/copies HPRT mRNA (range: 0.00-17.64) and 0.082 copies OPN-c mRNA/copies HPRT mRNA (range: 0.00-4.03). Comparison of the OPN splice variants mRNA expression levels clearly showed that OPN-a and OPN-b are expressed at a distinctly higher level than OPN-c (both with P < 0.01). The lower expression level of OPN-c is consistent with the findings in hepatocellular carcinoma, breast cancer and mesothelioma [12, 15, 16]. Furthermore, using bivariate linear Spearman-Rho correlation, we found a significant correlation of the mRNA expression levels between all OPN splice variants (r = 0.84-0.95, all with P < 0.01). Additionally, the mRNA expression level of total OPN and OPN splice variants show a weak correlation (n = 65, OPN-a: r = 0.32, P < 0.01; OPN-b: r = 0.30, P = 0.02; OPN-c: r = 0.26, P = 0.04).

                    In surrounding tissues of 15 STS patients we calculated a median transcript ratio of 0.66 copies OPN-a mRNA/copies HPRT mRNA (range: 5.80*10-2-30.19), 0.19 copies OPN-b mRNA/copies HPRT mRNA (range: 7.20*10-3-3.98) and 0.034 copies OPN-c mRNA/copies HPRT mRNA (range: 9.55*10-4-0.67). The median mRNA expression levels of OPN splice variants reveal that OPN-b and OPN-c in paired tumor tissues are expressed on a higher level compared to surrounding tissues (n = 15, p = 0.07 and p = 0.06). Figure 1 demonstrates a 2.9 and 3.4-fold increased mRNA expression level of OPN-b and OPN-c in tumor tissues. However, OPN-a mRNA expression level was not increased in tumor tissues (1.2-fold, p = 0.80). Several other studies confirm in tumor tissues a higher mRNA expression level of OPN splice variants than in surrounding or normal tissues [19, 20]. In agreement with our analysis, in breast cancer and ovarian cancer, especially OPN splice variants OPN-b and OPN-c are expressed on elevated mRNA levels compared to surrounding or normal tissues [10, 14, 15, 18].
                    http://static-content.springer.com/image/art%3A10.1186%2F1471-2407-12-131/MediaObjects/12885_2011_3156_Fig1_HTML.jpg
                    Figure 1

                    Comparison of mRNA expression of OPN splice variants in surrounding and tumor tissue. The boxplot shows the relative mRNA expression levels of OPN-a, OPN-b and OPN-c in tumor and paired surrounding tissues of 15 STS patients. The boxplot displays the median value of each data set, which is indicated by the centerline. The edges of the boxes represent the 25th percentile and 75th percentile. The 10th and 90th percentiles are marked through the horizontal lines outside the boxes. Circles and asterisks mark outliers (1.5 to 3 box lengths from the edge of the boxes) and far outliers (more than 3 lengths from the edge of the boxes).

                    Bivariate linear analyses of mRNA expression levels of OPN splice variants with clinical and histomorphological parameters

                    Examinations of the relation of mRNA expression levels of OPN splice variants with clinical and histomorphological parameters revealed a significant correlation of the mRNA expression level of OPN-a with sex and tumor grade (Table 1). More male patients have a low OPN-a mRNA expression level compared to female patients (P = 0.02, Table 1). Grade 3 tumors are strongly associated with high mRNA expression levels of OPN-a, OPN-b and OPN-c (P = 0.03, P = 0.05 and P = 0.03, respectively). The mRNA expression levels of the OPN splice variants were also significantly higher in high-grade gliomas than in low-grade gliomas [9, 17]. Recently, Patani et al. (2008) verified that the mRNA expression levels of OPN-b and OPN-c were also increased with higher tumor grade in breast cancer. Furthermore, we found that all patients with lymph node metastases had a significantly higher OPN-c mRNA expression level (P = 0.03). It is well known that OPN-c mediates anchorage independence and tumor invasion [10, 21], which are crucial processes for the development of metastases. Several studies showed that OPN-c is expressed at higher levels in invasive tumor cells compared to noninvasive tumor cells [13, 14, 17, 21]. Furthermore, it has been demonstrated in these studies that OPN-c influences the expression of several migration/invasion markers, such as MMP-2, MMP-9 and uPA, which promote tumor cell invasion. This is in accordance with the correlation we found between the OPN splice variants, the uPA, uPAR and PAI mRNA and the protein expression levels in STS (data not shown). Previously, we could show that the protein levels of uPA, uPAR and PAI in tumor tissue and serum are also associated with poor prognosis of STS patients [22]. However, we found no correlation between the mRNA expression level of OPN splice variants and the tumor stage, histological tumor subtype (Additional file 1), tumor localization or recurrence.

                    mRNA expression levels of OPN splice variants and disease-associated survival

                    We performed multivariate Cox's proportional hazard regression analysis to study the correlation between OPN splice variant levels and tumor-specific survival. The STS patients with high mRNA expression levels of the three OPN splice variants have a worse prognosis than those with low mRNA expression levels in their tumors. An elevated mRNA expression level of OPN-b or OPN-c is significantly correlated with a 2.1-fold or 1.8-fold increased risk of tumor-related death for STS patients, respectively (P = 0.02, CI = 1.2-3.6; P = 0.04, CI = 1.0-3.1) (Table 3). The mRNA expression level of OPN-a shows an association trend with the prognosis of STS patients (RR = 1.7, P = 0.06) (Table 3). Additionally, STS patients had worst prognosis when all OPN splice variants are expressed on high mRNA levels (data not shown). A study on 15 adult STS patients found a significant increase of total OPN mRNA levels in tumor tissues compared to normal tissues [5]. Another study on 41 osteosarcoma patients reported that higher OPN mRNA levels were associated with a worse prognosis [23]. However, our preceding data of 68 STS patients revealed that mRNA expression level of whole OPN did not significantly correlate with prognosis [8]. Up to now, the prognostic relevance of the OPN splice variants was only determined for breast cancer patients. The breast cancer patients with high mRNA expression levels of OPN-b or OPN-c had significantly shorter survival times than those with low mRNA expression levels [15]. Because we found much lower mRNA expression levels of OPN-a in the tumors of male patients (n = 56) than in those of female patients (n = 68), we performed sex-specific survival analyses (Table 3 and Figure 2A.). A multivariate Cox's regression model also revealed that female STS patients have a significantly worse prognosis than male STS patients. The women with high OPN-a or OPN-b mRNA expression levels have a 3.0-fold (P = 0.01, CI = 1.3-6.8) or 3.4-fold (P < 0.01, CI = 1.4-8.2) increased risk of tumor-related death, respectively. The different prognostic impact of the mRNA expression level in men and women is possibly caused by hormonal regulation of mRNA expression by female sex hormones or hormone receptors [24].
                    http://static-content.springer.com/image/art%3A10.1186%2F1471-2407-12-131/MediaObjects/12885_2011_3156_Fig2_HTML.jpg
                    Figure 2

                    Multivariate Cox's regression hazard analysis: Association of OPN splice variant mRNA expression levels with disease-specific survival of STS patients. Cox's proportional hazard regression models were adjusted to tumor stage, tumor entity, tumor localization and the expression of OPN-a, OPN-b or OPN-c for 68 female STS patients (A.) and 52 STS patients that received radiotherapy (B.). The median values were used as cut-off points to divide the STS patients into two groups: one with high and one with low (reference group) OPN mRNA levels in tumor tissues. A. Increased expressions of OPN-a and OPN-b are strongly associated with a 3.0-fold and a 3.4-fold increased risk of tumor-related death in female STS patients, respectively (P = 0.01, CI = 1.3-6.8; P < 0.01, CI = 1.4-8.2). The STS patients with an increased OPN-c expression level have a 2.3-fold (P = 0.07, CI = 0.9-5.4) increased risk of tumor-related death. B. In STS patients that received radiotherapy, elevated mRNA expression level of OPN-b and OPN-c are significantly correlated with an increased risk of tumor-related death (RR = 10.3, P < 0.01, CI = 2.0-53.7; RR = 11.4, P < 0.01, CI = 2.2-59.3). RT patients with an increased OPN-a mRNA expression level have a 3.5-fold increased risk of tumor-related death, but this result was not significant (P = 0.07, CI = 0.9-13.0).

                    Therapy of STS patients comprises surgical removal of the tumor and treatment with radio- and/or chemotherapy. To investigate the prognostic impact of the mRNA expression level of OPN splice variants prior to radiotherapy, we analyzed STS patients who received a curative radiotherapy (n = 52) (RT patients). In the Kaplan-Meier analysis, we found that the RT patients with low mRNA expression levels of all OPN splice variants have a significant survival benefit compared to those with high mRNA expression levels in their tumors (P < 0.05, Table 3). In addition multivariate Cox's regression models revealed that RT patients with high mRNA expression levels of OPN-b and OPN-c have a 10.3-fold and 11.4-fold increased risk of tumor-related death, respectively (P < 0.01, CI = 2.0-53.7; P < 0.01, CI = 2.2-59.3) (Figure 2B., Table 3). In the STS patients who did not receive radiotherapy (n = 62), the mRNA expression level of the OPN splice variants had no prognostic importance (data not shown). Consequently, the inhibiting of OPN could provide an additional survival benefit for STS patients who are treated with radiotherapy. Similarly, Overgaard et al. (2005) found that high OPN plasma concentrations are associated with a poor prognosis in patients with head and neck cancer after radiotherapy [25]. Our in vitro study verified the association of OPN and radiotherapy and proved that the inhibition of OPN mRNA expression increases the radiosensitivity of the mamma carcinoma cells [26].

                    Conclusions

                    In the present study, we found for the first time that the mRNA expression levels of OPN-b and OPN-c were significantly correlated with the clinical outcome of STS patients. Our data demonstrate that female STS patients and RT patients with low mRNA expression levels of OPN splice variants have a distinct survival benefit. In fact, the different roles of the OPN splice variants in angiogenesis, cellular invasion, cancer progression, and metastasis are widely discussed in the literature [14, 17, 18, 21, 27]. Further studies are needed to clarify why OPN splice variants have different effects on the prognosis of cancer patients.

                    In summary, our data suggest that high expression levels of OPN splice variants are negative prognostic and predictive markers, particularly for female STS patients and those who receive curative radiotherapy. However, more data are necessary to evaluate the OPN splice variants in the clinical management of STS patients.

                    Abbreviations

                    RR: 

                    Relative risk of tumor-related death

                    P: 

                    Probability

                    CI: 

                    95% confidence interval

                    r: 

                    Correlation coefficient

                    Declarations

                    Acknowledgements

                    We would like to thank our colleagues from the Department of Radiotherapy for their contribution to this study and their continuous support. This work was supported by the Wilhelm Sander Stiftung (grant number: 2007.123.1 and 2007.123.2) and by the Wilhelm Roux program of BMBF/NBL3 (grant number: FKZ: 20/11 and 23/27). H.T.'s work was supported by the Deutsche Krebshilfe (No. 107590).

                    Authors’ Affiliations

                    (1)
                    Department of Radiotherapy, Martin-Luther-University of Halle-Wittenberg
                    (2)
                    Centre for Reproductive Medicine and Andrology, Martin-Luther-University of Halle-Wittenberg
                    (3)
                    Department of Oral and Maxillofacial Plastic Surgery, Martin-Luther-University of Halle-Wittenberg
                    (4)
                    Department of General and Visceral Surgery, Diakoniekrankenhaus
                    (5)
                    Institute of Pathology, Dresden University of Technology
                    (6)
                    Clinic of Urology, FA University Hospital Erlangen
                    (7)
                    Nikolaus-Fiebiger-Center for Molecular Medicine, FA University Erlangen-Nürnberg

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                    28. Pre-publication history

                      1. The pre-publication history for this paper can be accessed here:http://​www.​biomedcentral.​com/​1471-2407/​12/​131/​prepub

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                    © Hahnel et al; licensee BioMed Central Ltd. 2012