Clinical prognostic factors for pediatric extra-abdominal desmoid tumor: analyses of 66 patients at a single institution

Desmoid tumor (DT), as previously named aggressive fibromatosis, is a rare soft tumor with a high rate of local recurrence and inability to metastasize [1, 2]. DT is a fibroblastic neoplasm that is derived from musculoaponeurotic structures. The annual incidence of this tumor is 2–4 per 1,000,000 persons with a peak incidence in women after pregnancy and abdominal location [3]. In our pediatric institute, we found that pediatric DT (PDT) was most commonly located in the buttocks and lower extremities [4].

According to previous studies, PDT has a higher local recurrence rate and is more difficult to control when compared with adult DT (ADT) [5, 6]. Patients with PDT have a higher incidence of local recurrence after surgery and different clinicopathological changes compared with adult patients [7, 8]. Some studies have shown that more gene mutations and higher gene mutation rate are observed in PDT compared with ADT [8]. So, the different genes and clinical phenotypes indicate that PDT may be a different disease from ADT.

Although DT is a benign tumor, its treatment is still a challenge because of the high local recurrence rate, especially in children [2, 7, 9]. Many treatments can be selected including surgery, radiotherapy, chemotherapy, and wait-and-see. However, each therapeutic option has its weaknesses and complications, especially in children [2, 7]. Data for adult patients are sufficient, and there are some guidelines for diagnosis and treatment and follow-up recommendations [10‐12]. However, it has been shown that PDT is more aggressive and difficult to treat than ADT [7, 13]. The data about treatment of PDT is limited, and prognostic factors are unclear.

In the present study, all patients were children, with extra-abdominal and deep tumors. The purpose of our study was to determine the prognostic factors for recurrence-free survival (RFS) in PDT at a single institution after macroscopic complete surgical resection.

DT is also known as aggressive fibromatosis and is divided into three types: extra-abdominal, abdominal, and intra-abdominal; or superficial and deep-type fibromatosis according to anatomical position [4, 5, 10]. Although the tumor does not develop distant metastasis, it has a high local recurrence rate after operation, and so it has been defined as a local malignant tumor. Some studies have shown obvious differences in pathogenesis and pathogenic site [13, 15]. A higher recurrence rate has been observed in pediatric patients [4, 16]. In the present study, all patients were children, and abdominal and intra-abdominal types were excluded because of different pathogenesis, and a high local recurrence rate (55%) was observed. However, clinical prognostic factors in PDT are still unclear and controversial. The present study was focused on exploring the clinical prognostic factors of PDT.

The first factor we investigated was sex. Most studies have shown that DT appears mostly in women, and this is no different in children [8, 17, 18]. However, in the present study, male patients were more frequent than female patients. These differences may be explained as follows. (1) All patients were children, with different pathogenesis from adult patients. Our previous research showed that the mutation rate of three exons of CTTNNB1 was higher in PDT than in ADT [4]. (2) Previous studies often included pediatric and adult patients, as well as all types of tumors [2, 14]. ADT most often occurs at abdominal and intra-abdominal sites in women after childbirth, and the prognosis is good [19]. The patients in the present study did not have these types of risk factors. Our study explored the relationship between sex and local recurrence. There was no significant sex difference in recurrence according to the χ² test. However, male sex was one of the risk factors for bad prognosis according to survival and multiple-factor analyses. This result differed from previous studies [9, 11, 12, 18, 20] and may have been because we had pediatric patients with extra-abdominal tumors. Sex is an important risk factor during treatment and should be considered in patients with extra-abdominal PDT.

The relation between age and prognosis of DT is controversial [7, 9, 12, 19]. In most studies, younger age was an important risk factor for local recurrence [19, 21‐23]. However, some studies have shown no relationship between age and local recurrence [9, 19]. In the present study, the younger patients had a higher recurrence rate. Although most studies and the present study showed that younger age at tumor presentation resulted in higher local recurrence rate, one study focused on pediatric patients suggested that older age increased postoperative local recurrence [7]. Patients in most other studies consisted of adults and children, and younger patients showed higher local recurrence rate. The reason may be that lower age group has some pediatric patients. Some authors have suggested that the high recurrence rate in younger patients is because pediatric patients have different and a higher number of gene mutations than older patients have [4, 8, 14, 24]. Moreover, DT cell proliferation decreased with older age. It is suggested that patients aged < 30 years need positive therapy with wide resection, additional therapy, and close follow-up [22, 25]. For older patients, less aggressive treatments such as partial resection, radiotherapy, and other less invasive methods, even wait-and-see, could be considered [26]. There have been few studies focused on pediatric patients, so the data for the prognostic effect of age for PDT are not sufficient. Our study suggested that age was an independent risk factor for local recurrence of PDT.

Tumor location is always an important risk factor for DT prognosis. There were obviously different groups in the present study in contrast to previous studies. In the present study, abdominal and intra-abdominal tumors were excluded. Extra-abdominal location, especially in the extremities, has been considered to be an independent risk factor that was associated with local recurrence of DT in previous studies [2, 7, 19, 23, 27]. PDT in the present study was divided into three groups according to location, including the buttocks, trunk, and upper and lower extremities. Tumors in the buttocks had poorest prognoses, and those in the trunk had the best. Moreover, PDT in the buttocks was most common in the present study and differed from adult patients in whom the tumor is often abdominal. These different clinical characteristics and prognoses suggest that tumors in different locations may have different biology or host-tumor site interactions. Different risk factors and location between pediatric and adult patients suggest that their tumors have different biological characteristics and are of different types [8]. The anatomical characteristics of the buttocks might be risk factors for higher recurrence. Tumors in the buttocks are often difficult to find by patients, so they may be large and deeply seated, even invading the pelvic cavity through the greater sciatic foramen, and adhering to the sciatic nerve. All of these factors may lead to tumor recurrence. PDT is more aggressive when it is adjacent to blood vessels and nerves, especially in the buttocks and lower extremities. These results confirmed that tumor location was a risk factor for recurrence. Tumors that are adjacent to blood vessels or nerves have poor prognoses that macroscopic tumor was completely resected and tumor cells may exist because of protecting important vessels or nerves during operation [28].

Tumor size was an important risk factor for prognosis. In the present study, the tumors were often large, especially in the buttock and lower extremities. The tumors were divided into three groups, and the results suggested that the larger tumors had a higher recurrence rate. Therefore, tumor size was a risk factor for poor prognosis. Previous studies have shown controversial results about tumor size. Most studies have suggested that large tumors are more aggressive, difficult to completely resect, adhesive to important blood vessels or nerves, and have a higher local recurrence rate [9, 19, 22, 29, 30]. However, some studies have shown that tumor size is not an independent risk factor for prognoses [7, 9, 23]. Tumor margin has been considered an important risk factor for prognosis. For large tumors adjacent to important blood vessels or nerves, complete resection is a challenge. It is difficult to define the tumor margin during surgery [30], although intraoperative frozen section examination is a reliable way. However, DT has a wide margin and intraoperative frozen sections have their limitations. Some studies have shown that tumor resection margin is not a risk factor for prognosis [7]. In the present study, we did not analyze the relation between tumor resection margin and local recurrence because all patients underwent macroscopic complete surgical resection.

Radiotherapy has always been controversial for treatment of DT, especially in children [7, 15, 17, 31]. Some studies have suggested that radiotherapy is effective for DT [15, 32‐34]. However, other studies have shown that radiotherapy is an uncertain factor for prognosis [2, 23, 27, 35]. For pediatric patients, potential complications of epiphyseal injury should be considered because of immature bones [7]. In the present study, because of care taken by the radiotherapist, only 27 patients received local radiotherapy. The radiotherapy dose range of 48–52 Gy was decided by a surgeon and radiotherapist. The results showed that radiotherapy significantly reduced the tumor local recurrence rate. Although we did not observe any complications of radiotherapy at the latest follow-up, we should be vigilant for epiphyseal injury in further follow-ups. PDT should be evaluated carefully for all risk factors before radiotherapy.

Treatment of PDT is a major challenge because of the high local recurrence rate and lack of clinical data focused on pediatric patients. Some studies have shown that PDT has a wider spectrum of gene mutations than ADT has [8, 14, 24]. Our previous study has confirmed that PDT has a higher number of mutations in exon 3 of CTNNB1 mutation than ADT, especially at the S45F site [4]. It has been demonstrated that gene mutation at S45F is related to tumor local recurrence. Gene mutation increases the difficulty of PDT treatment. We did not include this risk factor in the present study because of insufficient data about gene mutations in some patients. This was a limitation to the study and is a subject for further research.

There were some other limitations to the present study. First, it was a retrospective study. Second, the number of patients and time of follow-up were not adequate. Third, the therapeutic method was surgery and surgery plus radiotherapy, and chemotherapy was not prescribed.

All patients in the present study were children and had extra-abdominal type PDT. We evaluated the clinical characteristics and analyzed the risk factors for prognosis. The study could provide helpful advice to doctors who are formulating a therapeutic strategy for PDT patients.

There are some clinical risk factors for prognosis in pediatric extra-abdominal desmoid patients including age at presentation, gender, tumor location, and tumor size. Favorable therapeutic strategies could be selected according to the preoperative prognostic risk factors. Radiotherapy should be considered for the patients with local recurrence of PDT.