An infant inflammatory myofibroblastoma with TFG-ROS1 fusion: a case report

Abstract

Background

Inflammatory myofibroblastic tumors are extremely rare in the neck of infants, and pathological diagnosis may be challenging. Kinase fusions play an important role in the biology of many inflammatory myofibroblastic tumors, becoming an effective diagnostic method.

Case presentation

In this report, we present the case of an East Asian (Han Chinese) patient with rare infant inflammatory myofibroblastoma. DNA-based but not RNA-based next-generation sequencing was used to identify its targetable ROS1 fusions.

Conclusion

This case highlights the importance of simultaneously detecting DNA and RNA using next-generation sequencing in clinical practice.

Background

Inflammatory myofibroblastic tumors (IMTs) are rare intermediate (or low-grade) tumors, primarily originating in the abdomen and chest but also in the head and neck, central nervous system, or limbs [1]. Head and neck IMTs account for only 5% of all IMT cases [2]. IMTs are not age-limited but are relatively common in children and adolescents. IMTs have a risk of local recurrence but low risk of metastases (< 5%). The pathological diagnosis of IMTs is challenging. IMTs are mainly composed of differentiated myofibroblastic spindle cells with a large number of plasma cells and/or lymphocytes [3]. Immunohistochemically, IMTs are usually positive for vimentin, smooth muscle actin (SMA), and muscle-specific actin (MSA) but exhibit variable staining for desmin. In addition, anaplastic lymphoma kinase (ALK) positivity may be detected by immunohistochemical (ICH) staining. Molecularly, about 50% of IMT cases exhibit translocation of ALK gene [4] and a small portion are accompanied by fusion mutations in ROS1 and NTRK genes.

Here we report a case in which morphology and immunohistochemistry alone were not sufficient to make the final pathological diagnosis. It is necessary to combine relevant molecular pathological testing methods, especially next-generation sequencing (NGS) testing, to make the final pathological diagnosis.

Case presentation

On 8 October 2022, an East Asian (Han Chinese) baby boy was born by caesarean section because of “fetal distress” at 38 weeks gestational age and had weak breathing. Subsequently, 2 days later, he was intubated and put on a ventilator owing to the worsened breathing difficulties. Findings from the patient’s digital radiography (DR) examination showed that the bilateral lung transparency decreased, and the pulmonary markings were disordered and blurred, which were considered to be changes associated with neonatal pneumonia. The echocardiogram revealed left to right shunting at the atrial level, with a size of approximately 3.5 mm, suggesting patent foramen ovale or atrial septal defect. In addition, the echocardiogram showed there was a patent ductus arteriosus with a size of about 1.8 mm. On the right side of his neck, a 4 cm × 3 cm mass with clear boundary was palpable on physical examination. It was a hard, soft neck mass and had no resistance. He was subsequently referred to the hospital for further treatment. Computed tomography (CT) scan revealed a cystic low-density mass on the right side of the neck with a maximum slice size of 3.2 cm × 2.9 cm. Ultrasonography revealed a 34 mm × 36 mm × 12 mm hypoechoic mass on the right side of the neck and right mandible. The border was not clear, and the internal echocardiogram was not uniform.

Puncture pathologic diagnosis showed that the mass was a spindle cell tumor. Under a light microscope, the tumor cells were diffusely distributed histologically (Fig. 1A) and invaded the surrounding muscle tissue (Fig. 1B). The tumor cells were spindle-shaped with mild-to-moderate pleomorphism. There was no obvious nuclear fission observed, but hypertrophic fibroblast-like cells could be seen in some areas (Fig. 1D). Significant proliferation of collagen fibers in the tumor stroma with excessive infiltration of chronic inflammatory cells were defined (Fig. 1C). Immunohistochemistry (IHC) staining showed that β-Catenin, CD34, desmin, and Pan-TRK were positive (Fig. 2A–D). Whereas CK, EMA, myogenin, S100, TLE1, and ALK (D5F3) were negative (Fig. 2E–J). Ki67 and SMA were partially positive. On the basis of his IHC results and the tumor characteristics seen on light microscopy, the baby was diagnosed with spindle cell tumor.

Fig. 1

Histopathological features show that (A) the tumor cells were diffusely distributed histologically (100 ×) and (B) invaded the surrounding muscle tissue (200 ×). C Significant proliferation of collagen fibers in the tumor stroma with excessive infiltration of chronic inflammatory cells was defined (200 ×). D Hypertrophic fibroblast-like cells can be seen in some areas (400 ×)

Fig. 2

Immunohistochemical staining of the lesion demonstrated positive reactivity for (A–D) β-Catenin, CD34, desmin, and Pan-TRK and (E–J) negative expression for CK, EMA, myogenin, S100, TLE1, and ALK(D5F3). K, L In addition, Ki67 and SMA exhibited partly positive staining (200 ×)

After admission, the patient underwent symptomatic treatment. Meanwhile, RNA-based NGS and DNA-based NGS of the tumor tissue were performed, and TFG-ROS1 fusion mutation was detected by DNA-based NGS. The TFG-ROS1 fusion involved exons 1–4 of TFG and exons 35–43 of ROS (Fig. 3). In addition, mutations in CSMD3, FANCE, and other related genes (class III mutations) were also detected (Table 1). On the basis of his NGS results, the baby was finally diagnosed with IMT.

Fig. 3

TFG (chr3:100450850)-ROS1(chr6:117644569) fusion pattern

Table 1 Mutations detected by NGS

After receiving symptomatic treatment, the mass in the neck of the infant showed continuous enlargement. It was recommended that the patient be transferred to a higher-level medical facility for further treatment. However, following careful consideration, the parents of the patient requested to discontinue treatment and discharge the child from the hospital. Unfortunately, subsequent follow-up with the patient showed he had passed away.

Discussion

The diagnosis of IMTs poses certain challenges to clinical practice. IMTs lack specific clinical symptoms, and their histopathological morphology presents diverse characteristics. Although immunohistochemistry provides important diagnostic evidence, there are also challenges. In this case, positive β-Catenin staining may suggest the dysregulation of Wnt/β-Catenin signaling pathway. The positivity of CD34, desmin, and Pan-TRK further added to the complexity of the tumor cell lineage characteristics. The positive staining for CD34 may indicate a possible origin from cells with endothelial or mesenchymal stem cell-like properties. In addition, the positive staining for desmin suggested a myogenic component within the tumor. Pan-TRK positivity is interesting as it may point toward activation of the tropomyosin receptor kinase (TRK) pathway. However, the tumor cells were negative for markers of peripheral nerve sheath (S100 and SOX10) and rhabdomyoblastic (myogenin) and epithelial differentiation (CK). The Ki67 stain showed a 35% Ki67 index in the tumor cells. The overall findings support a locally aggressive fibro/myofibroblastic tumor. The differential includes a congenital fibrosarcoma and an IMT, and the former is favored because of the NTRK staining and high Ki67 index. The IHC staining profile provided a wealth of information, but molecular genetic evaluation was essential for accurate diagnosis.

The detection of the TFG-ROS1 fusion mutation by DNA-based NGS was a crucial finding. ROS1 encodes a transmembrane receptor, tyrosine kinase, which regulates cell proliferation, differentiation, migration, and apoptosis. ROS1 fusions result in ligand-independent, constitutive activation of its kinase domain. These fusions activate canonical cell survival and growth signaling pathways, including the RAS-MEK-ERK, JAK-STAT3, PI3K-AKT-mTOR, and SHP2 cascades [5]. ROS1 gene fusions are established drivers across diverse types of adult and pediatric cancers, such as non-small-cell lung cancer (NSCLC), cholangiocarcinoma, ovarian cancer, gastric adenocarcinoma, and colorectal cancer [6]. This case showed the genetic abnormality of TFG-ROS1 fusion, which is a helpful diagnostic marker in identifying IMTs. Previous reports revealed that molecular testing typically evaluates multiple genes potentially involved in kinase fusions and demonstrates greater efficacy compared with sequential immunohistochemical (IHC) staining [7].

In general, RNA-based NGS is the most efficient method for the detection of fusion gene. However, the break sites of TFG and ROS1 were in the intron region so that it was hardly detected by RNA-based NGS. When DNA-based NGS testing was performed, the TFG-ROS1 fusion variant was found. ROS1 still contained an active region composed of an intact kinase domain [8] where the TFG break point was located in the intron region between exons 4 and 5, and the ROS1 break point was located in the intron region between exons 34 and 35. This case suggests that for timely and broad testing of clinical samples, DNA and RNA based NGS assays can be performed simultaneously in clinical practice to instruct therapies [9].

Currently, the treatment of patients with advanced and unresectable IMTs is limited, and surgery is the main treatment. However, the implementation of molecular testing provides more treatment options for IMTs. ROS1 tyrosine kinase inhibitors (TKIs) (such as crizotinib and ceritinib) competitively bind to the adenosine triphosphate (ATP)-binding site of the ROS1 kinase, inhibit its phosphorylation and downstream signal transduction, and induce apoptosis and growth arrest of tumor cells. ROS1 TKIs in treating TFG-ROS1 rearrangement IMTs has been reported in limited reports. A 14-year-old boy diagnosed with pulmonary IMT had a significant reduction in tumor size and achieved persistent response (PR) with crizotinib [10]. A case report described a woman aged 22 years who was diagnosed with abdominal IMT and was negative for ALK IHC staining. In this case, the patient showed TFG-ROS1 fusion and was treated with ceritinib and achieved partial response with an excellent tolerance after 2.5 months [11].

In addition, it is worth noting that that Pan-TRK (+) was detected by IHC in this case, but fusion mutation of NTRK gene was not detected by RNA/DNA-based NGS, suggesting that Pan-TRK (+) does not represent fusion mutation of NTRK gene by IHC. It is necessary to verify this through other molecular pathological methods. In addition, alteration of CSMD3, FANCE, and other related genes was detected by DNA-based NGS in this case. The role of CSMD3 and FANCE in IMTs needs further research.

Conclusion

Molecular testing must be performed to identify other targetable oncogenic variations in cases where morphological and histological information cannot fully confirm the diagnosis. This case emphasized the importance of molecular validation in tumor diagnosis.