Abstract
Uterine sarcomas are rare but very aggressive. Uterine myomas, on the other hand, are the most common benign tumors of the uterus. Currently there is no diagnostic technique available to distinguish them with certainty. This study aimed to summarize the published literature concerning protein-based biomarkers in the peripheral blood that can assist in this difficult differential diagnosis. In total, 48 articles, published between 1990 and 2017, were included. Most studies (n=37) concerned soft tissue sarcomas, while 11 discussed uterine sarcomas specifically. Vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), interleukins (IL), cancer antigen 125 (CA 125), lactate dehydrogenase, gangliosides (LDH) and growth differentiation factor 15 (GDF-15) are the most studied proteins in soft tissue sarcomas, including uterine sarcomas. Future research on improving sarcoma diagnosis should include these proteins.
Uterine sarcomas are rare gynecological neoplasms and account for approximately 3-7% of uterine malignancies (1). They are mesenchymal tumors comprising leiomyosarcoma (LMS), endometrial stromal sarcoma (ESS), undifferentiated endometrial stromal sarcoma (UES) and adenosarcoma (AS). Carcinosarcoma (CSC) or malignant mixed müllerian tumor is now considered as a poorly differentiated epithelial tumor and will not be included in this review. Uterine sarcomas present with vague and non-specific symptoms due to their intramural localization. However, they are very aggressive and metastasize early. The overall survival is poor, especially for those having a high mitotic index. Reported 5-year survival rates are about 50% for FIGO stage I-II and only 20 and 10% for stage III and IV, respectively (2). Early diagnosis is hence very important, but a true challenge. A recent Norwegian cohort study of women diagnosed with uterine LMS showed that in 52% of patients, malignancy was not suspected at the time of surgery (3). It is a challenge, since approximately 70% of women develop uterine myomas (4). Although several features on ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) can raise suspicion, there is currently no diagnostic modality to distinguish between sarcomas and myomas with certainty (5). Sagae et al. (2014) showed that endometrial biopsy could diagnose LMS in only 35% and ESS in 25% of cases (6). Currently, no reliable predictive serum biomarkers have been identified. In daily practice, cancer antigen 125 (CA 125) is often used, however it is normally only significantly elevated in advanced disease. Therefore, it is a poor differential tool for uterine myomas and early-stage sarcomas (7, 8). Minimally invasive surgery is the surgical method of choice for myomas. Compared to open surgery, it is associated with less surgical complications, reduced blood loss, faster recovery, shorter hospital stays and fewer readmissions. During minimally invasive procedures, power morcellation is often required for tissue reduction. However, when a sarcoma is morcellated, proper pathological staging is precluded and tissue spilling within the abdominal cavity leading to local spread and recurrence may occur. In November 2014 the Food and Drug Administration (FDA) released a safety communication, discouraging the practice of morcellation of supposed myomas for oncological safety (9). This has led to a shift from minimally invasive surgery to open surgery with an increased economic burden and morbidity for patients with myomas. An American retrospective cohort study of 18,299 patients, undergoing hysterectomy for benign indications, analyzed the situation eight months after the FDA statement. They found a significant decrease of 4.1% in the use of laparoscopic hysterectomies and an increase in both abdominal and vaginal hysterectomies. This has led to a significant increase in major surgical complications from 2.2 (n=402) to 2.8% (n=512) and in readmission rate from 3.4 to 4.2% (10). Novel diagnostic methods capable of differentiating between myomas and sarcomas are needed for appropriate surgical planning. Protein biomarkers could form an interesting tool to help assessing the risk of uterine sarcoma in patients with presumed myomas. This study aimed to summarize the existing knowledge on biomarkers in the blood of sarcoma patients. Due to the low prevalence of uterine sarcomas, soft tissue sarcomas (STS) were also included in this analysis.
Materials and Methods
The PubMed database was used as a source. Search terms used were: uterine sarcoma, soft tissue sarcoma, marker, biomarker, diagnosis, serum, circulating, soluble, liquid biopsy, protein, immune and immunology. From the 2646 search results obtained in the period between 1990 and 2017, 419 abstracts were evaluated based on the title, 163 articles were read extensively, and 48 articles were eventually included. We included population-based studies that measured protein biomarkers in serum or plasma of soft tissue sarcoma patients, including uterine sarcomas. Articles on CSC only were excluded. Given the rarity of uterine sarcomas, studies were not limited by design, publication date or number of reported patients.
Results
A total of 37 studies in STS and 11 studies specifically in uterine sarcomas were identified. Results were divided in two main groups: cancer related and immune related protein biomarkers.
Cancer-related protein biomarkers
Role of cancer related protein biomarkers in cancer. CA 125 is a membrane glycoprotein associated with the coelomic epithelium, including the epithelium of the female reproductive tract. It is used as a tumor marker in the follow-up of ovarian cancer but has been shown to be non-specific [e.g. elevated in benign abdominal conditions, such as endometriosis (11), and in cardiac failure (12)]. Lactate dehydrogenase (LDH) is a pyridine-linked enzyme catalyzing the reduction of free pyruvate to lactate during glycolysis. Malignant cells proliferate rapidly and display an increased rate of glycolysis, independently of oxygen availability (Warburg effect). Furthermore, following cell damage, intracellular LDH leaks into the bloodstream (13). Insulin growth factor binding protein 7 (IGFBP7), also termed IGFBP-related protein-1, is a cell adhesive glycoprotein, mainly synthesized in the liver. Both increased and decreased expression of IGFBP7 have been reported in different malignancies, suggesting a complex role in cancer (14). Tumor cell gangliosides are cell surface glycolipids, that are overexpressed in solid tumors and are shed in greater quantities into the tumor microenvironment (15). Cadherins are cell–to–cell adhesion proteins, affecting tissue morphogenesis and structure. Tumor cells show decreased cadherin-mediated intercellular adhesions. This results in a loss of epithelial structure and gain of migratory capacity, potentiating invasion and metastasis. They are cleaved from the cell surface and released as soluble cadherins in serum (16, 17). The invasive capacity of tumor cells is related to the presence of matrix metalloproteinases that degrade extracellular matrix components and basement membranes. They are inhibited through endogenous specific tissue inhibitors of matrix metalloproteinases (TIMPs) (18).
Relevance of cancer-related protein biomarkers in the diagnosis of sarcomas. Table I gives an overview of studied non-immune related markers that have a potential role in the diagnosis of sarcomas. The most studied marker is CA 125. Three out of five studies have shown significantly higher CA 125 levels in the uterine sarcoma group compared to the patients with myomas (8, 19-22). Three studies have found statistically higher preoperative serum LDH levels in the uterine sarcoma group compared to patients with myomas (21-23) and two prospective studies showed significantly higher LDH levels in children with STS compared to healthy children (24, 25). One study found that patients with uterine myomas (n=24) had elevated serum LDH values, although this was not significant compared to serum levels in healthy controls (n=14) (26). In addition, three studies demonstrated that the combined use of serum LDH levels with different imaging modalities (fluor-18-deoxyglucose positron emission tomography (FDG-PET), PET-CT or MRI) increased the sensitivity and specificity of the preoperative diagnosis of uterine sarcomas and myomas, respectively (21, 22, 27). Nagai et al. (2015), proposed a preoperative diagnosis scoring system for uterine sarcomas [the PREoperative Sarcoma Score (PRESS)] using age at diagnosis, serum LDH levels, MRI findings, and endometrial cytology findings and revised it a year later (revised PRESS=rPRESS) (23). In the multivariate analysis of the original PRESS, MRI findings were not an independent predictive factor and hence were eliminated from the revised version, resulting in a better diagnostic accuracy. Table II shows an overview of the rPRESS. Patients were at higher risk for a sarcoma when their score was four or higher. The scoring system yielded an accuracy, sensitivity and specificity of 94%, 80% and 98%, respectively (23). Serum levels of gangliosides, soluble neural-cadherin (sN-CAD) and IGFBP7 were significantly elevated and levels of TIMP1/2 significantly decreased in sarcoma patients compared to healthy controls. However, only a limited number of studies are available for these biomarkers (28-31).
Overview of studied cancer-related protein biomarkers in serum or plasma in STS (including USC).
Overview of the revised PREoperative Sarcma Score (rPRESS).
Immune-related protein biomarkers
Role of immune-related proteins in cancer. Over the past years, the role of the immune system in cancer has become established. Tumor cells can be recognized and eliminated by both the adaptive and innate immune response. If cancerous cells are not eliminated, an equilibrium phase is established. Neoplastic cells remain present, but are constantly regulated by the immune system. During this process, tumor cells can lose tumor-associated antigens, while the tumor microenvironment can become more immunosuppressive and thereby the tumor can escape immune control. Immunosuppressive cells are attracted towards the tumor side (myeloid derived suppressor cells, regulatory T cells, M2 macrophages, etc.) and can even promote tumor growth (32, 33). Based on this theory, we can assume that cytokines, interleukins and chemokines, produced by these immune cells will be influenced by the malignant disease. Malignant cells can directly inhibit immune cell functions (by tumor growth factor β (TGF-β), interleukin (IL)-10, soluble IL-2 receptor α (sIL-2Rα), vascular endothelial growth factor (VEGF), etc.) or stimulate a pro-inflammatory environment (by IL-2, IL-6, IL-8 IL-12, IL-23, granulocyte colony-stimulating factor (G-CSF), macrophage colony-stimulating factor (M-CSF), tumor necrosis factor α (TNFα), etc.) (34). Tumor-promoting inflammation, mainly induced by innate immune cells, is considered one of the hallmarks of cancer (17). Clinical markers reflecting the inflammatory status of a patient are C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR). CRP is an acute-phase protein and its production in hepatocytes is induced following the elevation of IL-6 in response to stressors, such as infection or tissue damage (32). Several possible mechanistic links between elevated CRP levels and cancer have been proposed. On one hand, it could be a direct result of a growing tumor, causing inflammation. On the other hand, it might be mediated by the innate immune system. Finally, cancer cells can increase the production of inflammatory cytokines, which may induce CRP production (35).
Overview of studied immune-related protein biomarkers in serum or plasma in STS (including USC).
Overview of studied protein biomarkers in uterine sarcoma in serum or plasma.
As a side note, we want to stress the relevance of the neutrophil-to-lymphocyte ratio (NLR) as a diagnostic tool in sarcomas. This ratio has growing relevance in the diagnosis of several cancer types and in identifying patients with poor prognosis. Neutrophils are associated with the innate immune system and are often involved in immunosuppression (by suppressing the cytolytic activity of immune cells such as lymphocytes, activated T cells, and natural killer cells). The number of lymphocytes mirrors the effective adaptive immune system. Therefore, the NLR reflects the equilibrium between immunosuppression and immune activation. An elevated NLR represents an increase in the immunosuppressive status (36).
Tumor neovascularization, generated by the process of angiogenesis, is essential for the supply of nutrients and oxygen to the fast-growing tumor cells (17). VEGF and basic fibroblast growth factor (bFGF) promote angiogenesis. In addition to the production of pro-angiogenic cytokines, there is some evidence that STS can also release anti-angiogenic proteins, such as endostatin (37).
Death receptor 6 (DR6) belongs to the TNF receptor family and plays a key role in apoptosis induction. Yang et al. (2016), demonstrated that DR6 facilitates tumor growth by increasing angiogenesis through releasing IL-6 and VEGF-A (38). Growth differentiation factor-15 (GDF-15), also known as macrophage inhibitory cytokine-1, is a distant member of the TGF-β family. As a p53-regulated cytokine, it has been shown to have a role in the stress response of cells after cellular injury, for example in inflammation and cancer (39).
Relevance of immune related protein biomarkers in the diagnosis of sarcomas. Table III gives an overview of the studied immune related markers for sarcomas. Two prospective studies explored the pretreatment serum levels of several cytokines and soluble cytokine receptors in patients with STS compared to healthy controls. Both found significantly elevated pretreatment levels of 11 out of 13 tested cytokines and soluble receptors in the sarcoma group: interleukin-1 receptor antagonist (IL-1ra), sIL-2Ra, IL-6, IL-8, IL-10, TNFα, tumor necrosis factor receptor (TNF R) I and II, M-CSF, VEGF and bFGF. Soluble interleukin 6 receptor (sIL-6R) and G-CSF showed no significant changes in serum levels in the sarcoma group (40, 41). Serum levels of IL-1ra, IL-6, IL-8, Il-10, TNF RII and M-CSF decreased significantly after radical surgery in patients without metastases and after chemotherapy in patients with metastases (p=0.001) (41). Most studied immune related markers in STS are VEGF and bFGF. Eight and six studies reported significantly elevated serum VEGF and bFGF levels, respectively, in patients with STS compared to patients with benign soft tissue tumors or healthy controls (37, 40-46), while one study did not find a significant elevation in serum VEGF levels (47). Significantly elevated sIL-2Ra, IL-6 and IL-10 levels in the sarcoma group compared to healthy controls or patients with benign soft tissue tumors were found in four, three and four studies, respectively (24, 25, 40, 41, 48-50). Two studies reported significantly higher serum CRP levels in the STS group compared to benign soft tissue tumors and healthy controls (24, 51). In a study of 332 STS patients, the authors reported elevated CRP levels in 41% using a cut-off value of 0.1 mg/dl (52). Three other studies on 142, 102 and 162 STS patients, reported CRP levels >0.3 mg/dl in 25%, >0.3 mg/dl in 18%, and ≥0.2 mg/dl in 41% of patients, respectively (53-55). ESR has been limitedly studied. One study showed significantly elevated ESR levels in children with STS compared to healthy children (24).
Furthermore, one retrospective study has found a significantly elevated NLR in the STS group (n=83) compared to benign soft tissue tumors (n=140) (p<0.001) (56). In addition, two studies found significantly elevated NLR levels in the uterine sarcoma group compared to patients with myomas (20, 57). These two studies will be discussed in the next section.
DR6 and TGF-β have been limitedly studied in sarcomas. One study found significantly elevated DR6 levels in sarcoma patients compared to healthy controls (58) and one study found significantly elevated TGF-β in solid tumors, including 17 STS, compared to healthy controls (59).
Protein biomarkers in uterine sarcomas. Table IV gives an overview of available studies on protein biomarkers in uterine sarcomas specifically. Three out of five studies showed significantly higher serum CA 125 levels in the sarcomas group compared to patients with myomas (8, 19-22). Duk et al. (1994) analyzed pretreatment CA 125 levels in 30 patients with uterine sarcomas and found that only 40% had elevated serum levels (>16 U/ml) (7). Two studies found that there was a significant overlap regarding CA 125 levels between the early stage uterine sarcoma and myoma group (8, 19). Furthermore, three studies found statistically higher pretreatment serum LDH levels in the sarcoma group compared to patients with myoma (21-23). Kim et al. (2010) compared 55 patients with uterine sarcomas (21 CSC, 20 LMS and 14 ESS) to 165 with uterine myomas and 165 with adenomyosis in terms of age, body mass index and uterine volume and demonstrated that the preoperative blood NLR and neutrophil count were significantly higher, and the lymphocyte count significantly lower in the uterine sarcoma group compared to the myoma and adenomyosis group. Moreover, they observed a stronger predictive value of NLR compared to CA 125 (sensitivity, 74.5% vs. 52.3%; specificity, 70.3% vs. 50.5%; p<0.05) (20). Cho et al. (2015) compared 31 women with uterine sarcomas (14 ESS, 11 LMS, 6 USS) to 93 with uterine myomas and found statistically higher preoperative NLR values in the sarcoma group (57). Trovik et al., studied 19 patients with uterine sarcomas (13 LMS, four ESS, one AS and one USS), 50 with uterine myomas and 40 healthy controls and demonstrated a significantly higher median GDF-15 plasma concentration in the sarcoma group compared to the myoma group and healthy controls (60).
Discussion
The preoperative diagnosis of sarcomas limited to the uterus remains very challenging. For oncological safety, many women with myomas undergo open surgery instead of laparoscopic surgery, resulting in an increased morbidity and economic burden. On the other hand, minimally invasive surgery with morcellation of presumed benign myomas may lead to intra-abdominal spread of an unexpected sarcoma, resulting in poor survival. Proteins in serum or plasma are a potential tool to improve the preoperative diagnosis of uterine sarcomas. Measurement is easy, non-invasive and relatively inexpensive. The aim of this review was to give an overview of the existing literature on diagnostic biomarkers in uterine sarcomas. We have included 48 studies. Since uterine sarcomas are a subgroup of STS and information on uterine sarcomas only was very limited (only 11 studies), we have also included studies on non-uterine STS (37 studies).
It has become evident that the immune system has, besides its host-protective role, an influence on the development, progression and metastasis of cancers. The immune profiles in the tumor microenvironment of several types of sarcomas is a growing field of research. For example, Chen et al. (2018), found a possible role of the IL-33/IL-1 receptor-like 1 (ST2) axis in enhancing antitumor immunity in STS (61). More and more immunomodulatory drugs are being developed. For example, Ratti et al. (2017), demonstrated a decrease in monocytic myeloid derived suppressor cells in the tumor microenvironment (62). This review demonstrates the growing number of circulating protein biomarkers studied in the diagnosis of sarcomas. Most studied immune related biomarkers are VEGF, bFGF and interleukins. Despite the important role of TGF-β in immunosuppression in several other solid cancers (34), we found only one retrospective study measuring serum TGF-β levels in 17 STS among 66 different solid tumors (59). The median serum TGF-β levels at the time of diagnosis were higher in all groups compared to healthy controls. Despite the limited number of studies in sarcoma populations, NLR, representing an increase in the immunosuppressive status, may form an interesting diagnostic marker. Most studies on solid tumor biomarkers, specifically in uterine sarcomas, have examined CA 125, NLR, LDH and GDF-15. CA 125 is commonly measured in uterine sarcomas, but its usefulness is controversial due to the lack of specificity.
Given the small sample size, the mixture of various cancer types and the retrospective nature of many studies, the data should be interpreted with caution. Some studies performed in children may have a different tumor and immune biology (24, 25, 46, 48, 49, 59). Also, children have less comorbidities potentially affecting the proteins' serum levels. Most studies also compare STS or uterine sarcomas to healthy controls instead of to benign soft tissue tumors or uterine myomas, which does not reflect clinical reality. Furthermore, the markers' sensitivity and specificity are limited. Therefore, they would most likely benefit diagnosis in combination with other diagnostic modalities (such as ultrasound and MRI).
To the best of our knowledge, this is the first review on protein-based biomarkers in the blood of sarcoma patients. Although the number of available studies on protein-based biomarkers in uterine sarcomas is limited, interleukins, VEGF, bFGF, CA 125, LDH, gangliosides and GDF-15 are the most studied and significantly altered proteins in STS, including uterine sarcomas, compared to healthy controls, benign soft tissue tumors or uterine myomas. Further research to improve the sensitivity of preoperative uterine sarcoma diagnosis using multiplex assays should preferentially include these biomarkers.
Footnotes
Author's Contributions
NG performed the literature search, database set up and contributed to the writing of the manuscript. TB reviewed the manuscript. TvdB contributed to the study design and reviewed the manuscript. AC contributed to the study design, the writing of the manuscript and reviewed the manuscript. All authors are in agreement will all aspects of the final manuscript.
This article is freely accessible online.
Conflicts of Interest
The Authors declare no conflict of interest regarding this study.
- Received May 27, 2019.
- Revision received June 24, 2019.
- Accepted June 25, 2019.
- Copyright© 2019, International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved
