Firstly described in 1937, IMT is composed of proliferating spindle cells and accompanied with a surrounding fibroinflammatory process that typically occurs in children or young adults(5). This benign tumor has been reported to occur mostly in the lung. Nevertheless, multiple extrapulmonary cases have also been reported, the locations of the lesions of extrapulmonary IMT involve the upper respiratory tract, mesentery/omentum, urogenital tract, gastrointestinal tract, mediastinum, retroperitoneum, trunk, pancreas, liver and other areas(6). To our knowledge, there is few literatures reporting pediatric IMT originating from sigmoid colon.
The majority of IMTs are found incidentally in the chest or abdomen, with 15–30% patients presenting systemic symptoms such as pain, fever, weight loss and anemia(6, 7). Laboratory tests may reveal microcytic anemia, a raised erythrocyte sedimentation rate, thrombocytosis, and/or polyclonal hypergammaglobulinaemia(8). In some patients, the tumors may be found after an unknown-cause fever or growth failure(9). The systemic signs generally disappear or relieve after surgical excision, while the appearance of clinical and laboratory abnormalities is a warning sign for tumor recurrence(6, 9).
The etiologic factors responsible for the development and tumorigenesis of IMT are not clearly identified. Some researchers think that IMT development occurs after trauma, surgery or infection especially Epstein-Barr virus or human herpes virus, which are related with reactive cytokine production(10). Consequently, the presence of a true neoplasm in view of some investigators is considered as an immunologic response to infectious or noninfectious sources(11). Therefore, future efforts are required to classify this issue.
The diagnosis of IMT is difficult even at the microscopic level, thus immunohistochemical examinations are necessary to diagnose and differentiate IMT from other diseases, such as gastrointestinal stromal tumors, and inflammatory malignant fibrous histiocytomas(12, 13). Spindle-shaped cells with chronic inflammatory cells infiltration are considered as the characteristics of IMT(6). However, immunohistochemistry analysis, rather than radical, is important for definitive diagnosis of an IMT. The IMT cells are usually positive for desmin, vimentin, and smooth muscle actin (SMA), and frequently positive for ALK protein(4). The expression of ALK protein is a good diagnostic marker, while it is only present in about 50% of the patients with IMT(14, 15). Furthermore, the ALK-positive can also be seen in other types of carcinoma, such as rhabdomyosarcoma, and neuroblastoma(16). Therefore, the results of tumor cells collectively positive for SMA, ALK and desmin, negative for S100, sox10, CD117 and CD34, allow for the final diagnosis of IMT.
Nowadays, the total resection of the mass remains the essential therapy for the treatment of IMT. Besides surgery, a few cases have reported the curing by antibiotics, hormones or non-steroidal anti-inflammatory drugs(17–19). Recently, ALK directed therapy, as an alternative neo-adjuvant therapy, has been developed when the standard surgical treatment is not feasible. Furthermore, partial therapeutic effect on IMT has been described in previous studies(20–22). Nevertheless, the resistance to ALK inhibitor crizotinib appeared about 6 months after the initiation of the treatment when the patients had IMT with ALK rearrangement(20). With the further development of ALK inhibitors, the problem of crizotinib resistance can be solved, thus, the ALK inhibitors hold the promise to be a critical treatment to IMT.