Methods
Five cases of EIMS were retrieved from the archive files of the Department of Pathology, Fudan University Shanghai Cancer Center. The cases were initially diagnosed between 2012 and 2015 and were all consultation cases. The clinical and follow-up data were obtained from the electronic medical records, hospital discharge summary or by telephone inquiry. All available hematoxylin-and-eosin (H&E) slides were reassessed for cytomorphology, mitotic activity, composition of inflammatory infiltrate, stromal change, and presence of necrosis.
Immunohistochemical study was performed on paraffin-embedded sections on Ventana Benchmark XT autostainer (Roche). The primary antibodies used in the study included desmin (D33, dilution 1:500; DAKO), alpha smooth muscle actin (1A4, dilution 1:400; DAKO), muscle-specific actin (HHF-35, dilution 1:400; DAKO), H-caldesmon (h-CALD, dilution 1:400; DAKO), ALK (5A4, dilution 1:100; DAKO), CD30 (Ber-H2, dilution 1:50; DAKO), vimentin (V-9, dilution 1:200; DAKO), S100 protein (polyclonal, dilution 1:300; DAKO), pan-cytokeratin(AE1/AE3, dilution 1:100; DAKO), epithelial membrane antigen (E29,dilution 1:150; DAKO), myogenin(MYF4, dilution 1:500; Novocastra), CD117 (polyclonal, dilution 1:100; DAKO), discovered on GIST-1 (DOG1) (SP31, dilution 1:100; DAKO), CD34(QBEnd/10, dilution 1:50;DAKO) and Ki-67(MIB-1, dilution 1:150; DAKO). Appropriate positive and negative controls were run simultaneously for all antibodies tested.
Interphase fluorescence in situ hybridization analysis was carried out on 5-μm-thick sections of formalin-fixed, paraffin-embedded tissue in 5 cases, according to the manufacturer’s protocol. The presence of ALK gene rearrangement at 2p23 was tested using the LSI ALK dual-color break-apart probe (Abbott Molecular, Vysis, Des Plaines, IL). The fluorescence signals were analyzed using an Olympus BX51 fluorescence microscope (Olympus, Tokyo, Japan). A total of 100 nuclei were evaluated from each specimen.
Discussion
IMT is a well-described entity with a predilection for children and adolescents and occurs predominantly in the upper respiratory tract, lung and abdomen. Histologically, it is composed of spindled fibroblasts and myofibroblasts with occasional “ganglion-like” cells present in the tumor. IMT with prominent epithelioid cytomorphology is very rare. In a study with 73 cases of IMT, Cook et al. found 4 cases that exhibited round cell transformation characterized by large polygonal cells with large nuclei and prominent nucleoli, in a loose, pale staining background [
5]. In contrast to classic IMT, these four cases displayed more aggressive behavior. They proposed for the first time the nomenclature of “round cell transformation” to emphasize this distinctive feature. One of these 4 cases showed distinctive nuclear membrane staining pattern of ALK. Subsequent studies further demonstrated that this distinctive nuclear membrane staining pattern of ALK corresponded to ALK-RANBP2 fusions [
6-
8]. In 2010, Butrynski et al. reported sustained partial response to the ALK inhibitor crizotinib in a patient with ALK-translocated IMT with epithelioid cytomorphology [
9]. Their report indicated that this aggressive form of IMT merited a separation from the classic IMT. In 2011, Marino-Enriquez et al. [
4] described the clinicopathologic, immunohistochemical and genetic features of 11 additional cases in detail and proposed the designation as EIMS to highlight both the distinct morphology and malignant behavior of this aggressive form of IMT.
As EIMS has not been widely recognized, the incidence remains underestimated. To the best of our knowledge, only about 20 cases have been documented in the English literature [
4‐
12]. In this study, we describe a small series of 5 additional cases, increasing the number of reported EIMS to 25. The clinical features of these EIMSs are summarized in Table
1. Of these 25 cases, 18(72 %) patients were adults, and the other 7 patients were children and adolescents. Overall, the median and average ages of patients with EIMS were 34 and 30.7 years, respectively (range, 7 months-63 years). There was a prominent male predilection with a male to female ratio of 5.3:1. With regard to the location distribution, 21(84 %) tumors occurred in the intra-abdominal sites, including the mesentery, omentum, peritoneum, abdominal cavity and retroperitoneum, 3 in the organs (1 each in liver, rectum and transverse colon), and another 1 in the pleural cavity. The tumor size (unavailable in 5 cases) ranged from 5 to 26 cm in maximum diameter, with an average size of 13.2 cm.10 tumors were multifocal at the time of diagnosis, consisting of a large dominant mass and multiple small omental, mesenteric or peritoneal nodules. Clinically, patients usually manifested with abdominal pain or masses, sometimes with ascites.
Table 1
Clinical features of 25 cases of epithelioid inflammatory myofibroblastic sarcoma
1 | 7y/M | Abdominal cavity | NA | No | SE, CT | Yes (5w, 5 m) | No | NED(5 m) | |
2 | 7 m/M | Mesentery and omentum | 11 | Yes | SE | Yes (8 m) | No | AWD(8 m) | |
3 | 2y/M | Retroperitoneal and abdominal cavity | 10 | No | SE | No | No | NED(36 m) | |
4 | 34y/M | Liver | 8 | No | SE | Yes (5 m) | No | DOD(5.5 m) | |
5 | 44y/M | Omentum | NA | Yes | SE, CT, ALKi | Yes (5 m) | Liver (12 m) | AWD(39 m) | |
6 | 41y/M | Omentum | 26 | Yes | ST, CT, ALKi | Yes (12 m) | Liver(12 m) | NED(40 m) | Marino-Enriquez et al. [ 4] |
7 | 59y/M | Mesentery of small bowel | 15 | Yes | SE, CT | Yes | No | DOD (12 m) | |
8 | 6y/M | Omentum | 10.5 | No | SE, CT | Yes | No | AWD(3 m) | |
9 | 28y/M | Mesentery of small bowel | NA | Yes | NA | NA | NA | NA | |
10 | 63y/M | Mesentery of small bowel | 25 | No | SE, CT | Yes | No | DOD(3 m) | |
11 | 42y/M | Intra-abdominal | NA | No | SE, CT | Yes | No | AWD(13 m) | |
12 | 7 m/M | Peritoneum | 10 | No | SE, CT, RT | Yes | No | DOD(36 m) | |
13 | 40y/M | Peritoneum | 8 | No | SE, CT, RT | Yes | Lung, liver, and lymph node | | |
14 | 31y/M | Mesentery of small bowel | 17.5 | Yes | SE, CT | Yes | No | DOD(11 m) | |
15 | 6y/M | Omentum and mesentery | 14 | Yes | SE | NA | NA | NA | |
16 | 39y/M | Mesentery of small bowel | 15 | Yes | SE | NA | NA | NA | |
17 | 57y/M | Pleura or chest wall | NA | NA | ALKi | NA | NA | NA | |
18 | 19y/F | Mesentery of small bowel | 19 | No | SE | Yes(9w) | No | DOD(12w) | |
19 | 39y/M | Mesentery of colon | 15 | No | SE, CT | Yes(4 m) | No | AWD(12 m) | |
20 | 22y/M | Mesentery of small bowel | 6 | Yes | SE, CT, ALKi | Yes(3 m, 4 m) | No | AWD(14 m) | |
21 | 37/F | Rectum | 5 | No | SE | No(8 m) | No | NED(8 m) | Current cases |
22 | 55/M | Mesentery of ileum | 11 | No | SE, CT | Yes(2 m) | No | NED(10 m) | |
23 | 22/M | Mesentery of colon | 20 | Yes | SE, ALKi | Yes(2 m) | No | AWD(14 m) | |
24 | 58/F | Omentum | 5.5 | No | SE, CT | Yes(2 m) | No | DOD(8 m) | |
25 | 15/F | Transverse colon | 12 | No | SE | No(7 m) | No | NED(7 m) | |
EIMS has distinctive morphological features. The tumor is typically characterized by loosely arrayed, round or epithelioid neoplastic cells with vesicular nuclei, prominent large nucleoli and amphophilic to eosinophilic cytoplasm distributed in a widespread myxoid stroma. The striking feature of EIMS is the presence of obvious inflammatory infiltrates frequently composed of neutrophils. All tumors almost contained a small amount of spindle cell component. Immunohistochemically, EIMS demonstrated a unique nuclear membrane staining pattern of ALK, which was observed in 80 % (20/25) of cases (Table
2). However, several cases (20 %, 5/25) showed ALK perinuclear or cytoplasmic staining pattern. Another diagnostic immunophenotype is diffuse and strong expression of desmin in almost all cases (86.4 %, 19/22). In addition, the tumor displayed variable expression of CD30 (61.1 %, 11/18), alpha smooth muscle actin (47.4 %, 9/19) and cytokeratin (15.8 %, 3/19).
Table 2
Immunohistochemical and genetic features of 25 cases of epithelioid inflammatory myofibroblastic sarcoma
1 | NA | NA | NA | NA | NA | NA | NA | NA | NM+ | + | RANBP2-ALK |
2 | NA | NA | NA | NA | NA | NA | NA | NA | NM+ | + | RANBP2-ALK |
3 | + | + | - | NA | + | NA | - | NA | PN+ | + | RANBP2-ALK |
4 | - | - | NA | - | - | NA | - | NA | NM+ | NA | RANBP2-ALK |
5 | + | - | NA | + | - | - | - | - | NM+ | + | RANBP2-ALK |
6 | + | - | - | + | - | - | - | - | NM+ | + | RANBP2-ALK |
7 | + | + | NA | NA | - | NA | - | - | NM+ | + | NA |
8 | + | - | NA | NA | - | NA | - | - | NM+ | + | NA |
9 | + | + | NA | + | - | - | - | NA | NM+ | NA | NA |
10 | + | - | - | + | - | - | - | - | PN+ | + | NA |
11 | + | NA | NA | NA | NA | NA | NA | NA | NM+ | NA | NA |
12 | + | NA | - | + | NA | NA | NA | - | PN+ | + | NA |
13 | - | + | - | + | - | - | - | - | NM+ | + | NA |
14 | + | - | - | + | - | NA | - | - | NM+ | + | NA |
15 | + | NA | - | + | NA | NA | NA | NA | NM+ | + | RANBP2-ALK |
16 | + | + | - | + | - | NA | - | - | NM+ | + | RANBP2-ALK |
17 | + | - | NA | - | + | NA | - | NA | PN+ | + | NA |
18 | + | + | - | + | - | - | - | - | NM+ | + | NA |
19 | + | + | - | + | - | - | - | - | NM+ | + | RANBP2-ALK |
20 | NA | NA | NA | NA | NA | NA | NA | NA | NM+ | NA | RANBP2-ALK |
21 | + | - | - | - | - | NA | - | - | NM+ | + | NA |
22 | + | - | NA | - | - | - | - | - | NM+ | + | NA |
23 | + | - | - | - | - | - | - | - | PN+ | + | NA |
24 | + | Focal + | - | - | Focal + | NA | - | - | NM+ | + | NA |
25 | - | + | NA | - | - | - | - | - | NM+ | + | NA |
Total | 86 % (19/22) | 47 % (9/19) | 0 % (0/13) | 61 % (11/18) | 16 % (3/19) | 0 % (0/10) | 0 % (0/19) | 0 % (0/16) | 100 % (25/25) | 100 % (21/21) | 100 % (10/10) |
Approximately 50 % of IMTs aberrantly express ALK protein triggered by clonal rearrangements of ALK gene located on chromosome 2p23 [
3]. A variety of ALK partner genes have been subsequently identified in IMT owing to diverse chromosomal rearrangements, including TPM3 at 1p23, TPM4 at 19p13, CLTC at 17q23, CARS at 11p15, ATIC at 2q35, SEC31L1 at 4q21, PPFIBP1 at 12p11 and ran-binding protein 2 (RANBP2) at 2q13 [
13‐
17]. Different fusion partners may result in distinct ALK staining pattern when detected by ALK antibody. IMT with TPM3, TPM4, CARS, ATIC, and SEC31L1 fusion often shows diffuse cytoplasmic staining of ALK [
5,
6], whereas with CLTC fusion, displays granular cytoplasmic staining [
14]. By comparison, EIMS harbors a specific RANBP2-ALK fusion genes resulting from t (2;2) (2q12;2p23). All 21 cases tested by FISH so far showed positive signal of ALK translocation. Of note, all 10 cases in which the cDNA fusions were examined by reverse transcription-polymerase chain reaction (RT-PCR) constantly presented identical fusion points between exon 18 of RANPB2 and exon 20 of ALK (Table
2). The fusion partner of RANBP2 encodes a nuclear pore protein, attributing to the nuclear membrane or perinuclear staining pattern in EIMS. 9 cases except for one confirmed by RT-PCR in previous studies reported to contain RANBP2-ALK fusion showed this distinct staining pattern [
4-
9,
11,
12]. The biology function of the RANBP2-ALK fusion protein remains largely unknown. Several studies discovered that the chimeric RANPB2-ALK gene could promote cell growth and proliferation independent of cytokine in vitro [
18,
19]. Furthermore, nearly all reported cases containing RANBP2-ALK fusion gene pursued an aggressive behavior [
4,
5,
7,
9,
11,
12]. Accordingly, we infer that RANPB2-ALK fusion gene might be a potential molecular mechanism for the rapid growth and recurrence of EIMS. However, further investigations are still needed to establish the relationship this fusion gene with aggressive clinical course of EIMS.
EIMS can be diagnosed in combination with morphologic features and an appropriate immunohistochemical panel. Nonetheless, it is possibly risky to diagnose EIMS rely solely on the histology or ALK expression, because not all IMTs with epithelioid/round cell morphology carry the genetic alteration of EIMS [
5], as well as ALK cytoplasmic staining could be encountered in a few mesenchymal tumors, such as rhabdomyosarcoma, malignant peripheral nerve sheath tumor, leiomyosarcoma, lipogenic tumors, and Ewing sarcoma/ peripheral primitive neuroectodermal tumor [
20,
21]. Therefore, for those cases with atypical morphology or immunoprofile, we recommend further genetic detection of ALK rearrangement by FISH or RT-PCR to confirm the diagnosis of EIMS.
A variety of tumors should be included into the differential diagnoses of EIMS. Anaplastic large cell lymphoma (ALCL) is the most likely to be confused with EIMS, because both tumors have an overlapping immunophenotype and cytogenetic feature, including reactivity for CD30, ALK and SMA, and the presence of ALK rearrangement [
22]. Detection of ALK translocation by FISH would not be helpful in the distinction of both tumors. However, strong expression of desmin and nuclear membrane ALK staining are not observed in ALCL. Moreover, ALCL is absent of RANBP2-ALK fusion gene in EIMS, which can be detected by RT-PCR. In addition, epithelioid leiomyosarcoma also needs to be differentiated from EIMS, but the former usually contains at least focal areas of typical spindle cell leimyosarcoma and is lacking of ALK nuclear membrane expression. Other tumors with round or epithelioid morphology may also be discriminated from EIMS, such as solid variant of alveolar rhabdomyosarcoma, epithelioid gastrointestinal stromal tumor, epithelioid malignant peripheral nerve sheath tumor, myxoid/round cell liposarcoma, myxofibrosarcoma, poorly differentiated carcinoma, and melanoma. However, these entities can be easily distinguished by their lack of nuclear membrane ALK staining and their respective morphology and immunophenotypes.
With respect to the biologic behavior of EIMS, 8 of 21 patients with follow-up information died of the disease (6 within 1 year of diagnosis, 2 within 3 years of diagnosis), 7 was alive with disease, and the other 6 remained well with no evidence of disease [
4-
9,
11,
12]. The median time of overall survival was 11 months (mean, 15.4 months). Furthermore, 18 patients experienced local recurrence, and 3 developed distant metastases (2 to liver, 1 to lung, liver and lymph node) [
4,
5,
7,
9,
11,
12]; its local recurrence rate (86 %, 18/21) and distant metastasis rate (14 %, 3/21) are both markedly higher than those of the conventional IMT. The data indicate that EIMS pursues a more aggressive biologic behavior than the usual IMT. Up to present, the clinicopathologic factors related to prognosis of EIMS is still unknown. Several studies suggested that its abdominopelvic origination, bigger tumor size, epithelioid morphology and RANBP2-ALK are possibly related to its aggressive course [
4,
5,
7,
9,
11,
12,
23].
The optimal therapy of EIMS has not been well established. A surgical resection remains to be considered as the mainstay of treatment. In view of postoperative adjuvant therapy, available experiences are very limited. Most of reported cases are administrated by postoperative chemotherapy or radiotherapy, but it seems to have no obvious effects in the control of rapid recurrence [
4,
7,
9,
11,
12]. Recently, ALK inhibitor, crizotinib, has been applied in the treatment of EIMS with certain effectiveness [
4,
9,
10,
12,
24]. Thus, crizotinib might serve as a provisional adjuvant in the therapy of EIMS. In our own series, case 3 was treated with ALK inhibitor (crizotinib) after the recurrence. Follow-up CT scan showed that the residual tumor partially shrinked in size. The patient felt well after four courses of treatment.