Background

Desmoid tumors are rare clonal fibroblastic proliferations that arise in the extremities, girdles, chest, abdominal wall, and neck. They are characterized by infiltrative growth and a high risk of local recurrence even after complete surgical excision[1]. Several reports have suggested a link between cyclooxygenase-2 (COX-2) expression and the proliferation of desmoid tumors[2, 3]. These findings provide clinical evidence for the use of COX-2 inhibitors in the treatment of desmoid tumors. Most patients present with an asymptomatic, firm, poorly circumscribed mass, but some complain of severe tumor-associated pain. These painful masses often cause decreased joint mobility and functional impairment. COX-2 converts arachidonic acid into prostaglandins, the major modulator of pain. In this study, the hypothesis that COX-2 regulates desmoid tumor-associated pain was examined by immunohistochemical evaluation of COX-2 expression in tumor samples. The relationship between intratumoral COX-2 expression and pain status was evaluated.

Materials and methods

For the use of these clinical materials for research purposes, prior consent from the patients and approval from the Institutional Review Board of Sapporo Medical University Hospital was obtained.

Subjects

The study included 16 patients who were treated and followed up at our hospital between April 2003 and May 2010. Needle and/-or open biopsies were performed to confirm the diagnosis of desmoid tumor. Clinical details and follow-up information were obtained by reviewing the patients’ medical charts. All information on tumor-related pain was recorded at presentation.

Immunohistochemical analysis

COX-2 protein expression in desmoid tumors was determined by immunohistochemistry. Immunohistochemical analysis was performed using the labeled streptavidin-biotin method and tissue sections from paraffin blocks. Immunophenotyping for COX-2 and tryptase was performed using monoclonal mouse primary antibodies for COX-2 (BD Biosciences, San Jose, CA; 1:500) and tryptase (Dako Corp., Glostrup, Denmark; 1:200). Mast cells were identified by tryptase staining. Several previously characterized chondrosarcoma samples were used as positive controls. The immunohistochemical results were evaluated by a pathologist (MT) who was blinded to the patient’s clinical status. The number of COX-2 positive cells in 10 consecutive fields was counted at 400× magnification. The patients were stratified into 2 groups according to the number of COX-2 -positive cells, the COX-2 positive group (≧10 COX-2 -positive cells) and the COX-2 negative group (<10 COX-2 -positive cells)

Statistical analysis

The chi-squared test was used to examine the correlation between COX-2 expression in desmoid tumors and pain. Statistical significance was defined as p < 0.05. Data were analyzed using IBM SPSS Statistics (IBM Corp., Armonk, NY).

Results

Clinical characteristics

Details of the clinical features are reported in Table 1. The patients were 2 men and 14 women, 16–80 years of age (median, 36 years). The tumors were located in the back (n = 5), abdominal wall (n = 2), leg (n = 3) [thigh, 2; lower leg, 1], arm (n = 1), axilla (n = 1), and anterior chest wall (n = 1). Treatment procedures consisted were wide resection (n = 4), resection biopsy (n = 2), and simple observation (n = 10). Seven patients (case 2, 3, 7, 10, 11, 12, and 15) complained of tumor pain.

Table 1 Details of the clinical features
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Immunohistochemical analysis

Immunohistochemistry demonstrated no positive staining for the COX-2 protein within the tumor cells of all samples from the 16 patients (Figure 1). In contrast, several small, round COX-2 -positive cells were detected within the tumoral stroma (Figure 1). COX-2 -positive cells were similar in morphology to mast cells. Therefore, we performed immunohistochemical staining for tryptase in co-localized sections. As shown in Figure 2, tryptase staining was seemed coincided in the COX-2 -positive cells, suggesting that COX-2 proteins were expressed in tryptase-positive mast cells inside the desmoid tumors, and not in the tumor cells themselves. Six out of 7 patients in the COX-2 -negative group had painless tumors. In contrast, 6 out of 9 patients in COX-2- positive group had painful tumors. This difference was statistically significant as assessed by the chi-squared test (Table 2, p = 0.036), suggesting a positive correlation between COX-2 expression and tumor-associated pain.

Figure 1
figure 1

Immunohistochemistry demonstrated no positive staining with COX-2 protein within the tumor cells (X100, (a) Hematoxylin and eosin and (b) COX-2).

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Figure 2
figure 2

Tryptase clearly co-expressed in the COX-2 positive cells (X100, (a) COX-2 and (b) tryptase).

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Table 2 COX-2 expression and tumor-related pain
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Discussion

Mast cells are mobile cells derived from bone marrow that circulate in the blood. Mature mast cells are scattered throughout tissues, including connective tissue[4]. The role of mast cells in connective tissue is still a matter of speculation, and it has been suggested that these cells participate in cell regulation and control of the accumulation of connective tissue components. Several reports indicate that mast cells are potentially fibrogenic, since they secrete potent mediators of fibrosis[5, 6]. One of the main components of the secretory granules of mast cells is tryptase[7], an enzyme found exclusively in these cells. Tryptase is involved in diverse biological activities such as fibrogenesis and stimulation of fibroblast proliferation[8, 9]. These findings suggest that mast cells are involved in the pathogenesis of desmoid tumors through the action of tryptase, a mast cell-derived protease. Recent studies have shown that tryptase induces COX-2 expression by the specific cleavage of protease-activated receptor-2[10, 11]. COX-2 expression is significantly elevated in several neoplasms, including desmoids tumor[2, 3]. COX-2 overexpression leads to increased prostaglandin E2 production, which in turn promotes the growth of desmoid tumors. Furthermore, treatment with COX-2 inhibitors induces the shrinkage of desmoid tumors.

Recent reports have demonstrated that desmoids tumor cells express COX-2 protein[2, 3]. However, we failed to show the expression of COX-2 protein within the tumor cells. Conversely, COX-2 -positive mast cells were identified within the desmoid tumors. In addition, a positive correlation between COX-2 expression and tumor-related pain was observed, suggesting that COX-2 secretion from mast cells, not tumor cells, may modulate desmoid tumor-related pain. In addition, there could be connection between mast cells, at least in part, and the pathogenesis of desmoids tumors.

In conclusion, these results suggest a link between clinical symptoms and the tumor microenvironment in desmoid tumors via the secretion of COX-2 from mast cells.