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Year : 2022  |  Volume : 65  |  Issue : 3  |  Page : 695-698
Novel ALK-EML4 fusion with prominent mucous and hyaline stroma: Expanding the molecular genetic spectrum of S100 and CD34 positive spindle cell tumor

1 Department of Pathology, Huashan Hospital of Fudan University, Shanghai, India
2 Department of Gynaecology, The Third Affiliated Hospital of Second Military Medical University (Eastern Hepatobiliary Surgery Hospital), Shanghai, People's Republic of China

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Date of Submission17-Jun-2021
Date of Decision20-Jun-2021
Date of Acceptance02-Aug-2021
Date of Web Publication21-Jul-2022


We report a case of a 49-year-old male patient suffering from an intraspinal tumor in the lumbar vertebra. The neoplasm was composed of mono-morphic spindle cells, arrayed in a patternless pattern in a background of prominent myxoid hyaline stroma with perivascular collagen rings in hyper-cellular regions. Instead, aggregated collagen fibers arranged into nodules and apparent calcium deposition were found in hypo-cellular regions. The tumor cells showed immunopositivity with S100 and CD34, whereas lacked SOX10 expression, which were reminiscent of a group of S100 and CD34 co-expression soft tissue spindle cell lesions having recurrent fusions including RAF1, BRAF, NTRK1/2/3, and RET genes. Interestingly, a novel anaplastic lymphoma kinase (ALK)- echinoderm microtubule-associated protein-like 4 (EML4) gene fusion was revealed. To our best knowledge, it was the first time to identify such gene fusion in the Orientals among this mentioned group, and it expands the molecular genetic spectrum of this specific group. The clinical relevance of this novel fusion requires further investigations.

Keywords: ALK-EML4, CD34, S100, spindle cell tumor, soft tissue

How to cite this article:
Sun R, Hu R, Xiong J, Wang Y. Novel ALK-EML4 fusion with prominent mucous and hyaline stroma: Expanding the molecular genetic spectrum of S100 and CD34 positive spindle cell tumor. Indian J Pathol Microbiol 2022;65:695-8

How to cite this URL:
Sun R, Hu R, Xiong J, Wang Y. Novel ALK-EML4 fusion with prominent mucous and hyaline stroma: Expanding the molecular genetic spectrum of S100 and CD34 positive spindle cell tumor. Indian J Pathol Microbiol [serial online] 2022 [cited 2022 Oct 7];65:695-8. Available from:

   Introduction Top

So far, a reported group of spindle cell neoplasms characterized by a relatively uniform cytomorphology, pattern-less architecture, conspicuous stromal and perivascular hyalinization, with S100 and CD34 co-expression, and recurrent fusions involving RAF1, BRAF, and NTRK1/2 genes have been depicted.[1] In our files, we found a rare case with similar morphology co-expressing CD34 and S100, but showing echinoderm microtubule-associated protein-like 4 (EML4)- anaplastic lymphoma kinase (ALK) fusion. EML4-ALK was widely discovered in non-small cell lung cancer (NSCLC). However, it was sparsely reported in soft tissue tumors (STTs) including inflammatory myofibroblastic tumors (IMTs), not to mention in those harboring CD34 and S100 coexpression.

   Case History Top

A 49-year-old man presented to neurosurgery clinic with low back pain, spreading from the left leg to the sole for at least 2 months. Physical examination showed hypoalgesia in the left lower limb. Computed tomography (CT) imaging identified an irregular mass spanning from L3 to S1. It involved centrum and spinous with extension to paravertebral soft tissue. It measured about 14 × 8 × 6 cm [Figure 1]. Owing to the location, it was subtotally resected. Postoperatively, the patient received radiotherapy and underwent CT scanning 3 months later. The patient was alive without clinical progression after 15 months of follow-up.
Figure 1: CT examination of the primary lesion shows a giant mass spanning from L3 to S1 with bone destruction

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Grossly, the faint solid yellow specimen was well-circumscribed and measured 13 × 9 × 3 cm. Microscopically, the hyper-cellular areas showed a monomorphic spindle cell histology with prominent myxoid hyaline stroma and perivascular collagen rings [Figure 2]a and [Figure 2]b. Fibroblasts and myofibroblasts were arranged in mostly haphazard growth patterns and were separated by band-like collagen [Figure 2]c. The spindle cells manifested plump oval to elongated and mildly pleomorphic nuclei with vesicular chromatin, accompanied by inconspicuous cell borders [Figure 2]d. Low mitotic activity was present with 1 mitosis per 10 High Power Field (HPF). Necrosis was absent. Notedly, there was plenty of calcification, especially appearing in the collagen aggregation area, and medium-size vascular walls were invaded by myxoid hyaline component [Figure 2]e and [Figure 2]f. The tumor cells were diffusely positive for CD34 and S100, and ALK immunostaining exhibited mild to moderate cytoplasmic staining, whereas it was negative for SOX10 [Figure 2]g, [Figure 2]h, [Figure 2]i, [Figure 2]j. In addition, the tumor cells were negative for glial fibrillary acidic protein (GFAP), neurofilament proteins (NF), epithelial membrane antigen (EMA), signal transducer and activator of transcription 6 (STAT6), Desmin, smooth muscle actin (SMA), and caldesmon. The result of fluorescence in situ hybridization (FISH) indicated ALK rearrangement [Figure 3a], and ALK-EML4 rearrangement was discovered [Figure 3]b. In summary, the case was diagnosed as “Low grade malignant soft tissue tumors with CD34 and S100 coexpression, harboring ALK-EML4 fusion.”
Figure 2: The tumor arranging in a mostly haphazard growth pattern showed a monomorphic spindle cell histology with prominent myxoid hyaline stroma, (a) (HE stains, × 40), and perivascular collagen rings, (b) (HE stains, × 100). Longitudinal or nodular collagen fibers surrounded by a few layers of fibroblasts were in the myxoid stroma, (c) (HE stains, × 40). The cells had plump oval to elongated and mildly pleomorphic nuclei with vesicular chromatin, moderate volumes of pale amphophilic cytoplasm, (d) (HE stains, × 400). Calcification appeared in collagen aggregation area, (e) (HE stains, × 40), and myxoid hyaline component infiltrated medium-size vascular walls, (f) (HE stains, × 200). The tumor cells were diffusely positive for ALK-1, (g) (immunostain for ALK-1, × 200), CD34, (h) (immunostain for CD34, × 200), and, S100, (i) (immunostain for S100, × 200), respectively. SOX10 is negative, (j) (immunostain for SOX10, × 200)

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Figure 3: The result of ALK (2p23) break-apart FISH probe analysis indicated ALK re-arrangement (In interphase nuclei, one red, one green, and one yellow signal were observed.), (a). Next-generation sequencing (NGS) presented ALK-EML4 rearrangement, (b)

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   Discussion Top

Recently, a group of STTs showing CD34/S100 co-expression immunophenotype covered the range from bland, low-grade to ample, mitotically active tumors. However, the connections between them were patternless architecture, uniform cytomorphology, perivascular hyalinization, and conspicuous stroma, accompanied by the presence of recurrent gene fusions including RAF1, BRAF, and NTRK1/2.[1]

The morphologic features in our case overlapping with the NTRK-rearranged mesenchymal neoplasms were haphazardly arranged primitive cells in a variably myxoid stroma and/or spindled cells arranged in fascicles (dominant features), mixing with one or multiple secondary morphologic patterns. The rare morphologic patterns included biphasic pattern, nuclear palisading, a collagenous stroma, and prominent perivascular hyalinization.[2] The co-expression of S100 and CD34 with the absence of SOX10 were prominent features in this group, but ALK immunohistochemistry positivity was rarely found. Subsequently, next-generation sequencing panel (NGS) fusion panel identified an ALK-EML4 rearrangement, which demonstrated a linker between exon 6 of EML4 and exon 20 of ALK, and the result was verified by ALK immunostaining and FISH in succession.

ALK rearrangement was identified in different cancers, including non-small-cell lung cancer (NSCLC), diffuse large B-cell lymphoma, inflammatory myofibroblastic tumors, and so on.[3] Due to gene rearrangements, an oncogenic ALK tyrosine kinase–activated multiple downstream known cancer signaling pathways, such as PI3K/AKT, JAK/STAT, and RAS/RAF/MEK/ERK,[4] result in increased cell proliferation and metabolism, cytoskeleton remodeling, migration, survival, and apoptosis avoiding.[5]

Furthermore, a myxoid component often occurred in ALK-rearranged tumors. According to the IMTs in the uterus, the most characteristic features were the myxoid pattern, composed of plump spindle cells with an edematous matrix in a prominent myxoid.[6] Besides, it also appeared in lung adenocarcinomas with predominant mucinous or signet-ring cells.[7] This observation was consistent with studies that reported a link between ALK rearrangement and lung carcinomas with mucinous features, including signet-ring cells and extracellular mucin.[8],[9] Our reported case with abundant myxoid hyaline stroma partially owed to ALK-EML4 fusion; however, large-scale studies are still needed to verify the association between ALK rearrangement and myxoid component.

IMTs display a wide morphologic spectrum, ranging from an inflammatory “pseudotumor” with predominant hyalinization and chronic inflammation to a highly cellular myofibroblastic proliferation. Antonescu and his colleague studied a cohort of 62 cases previously diagnosed as IMT including 35 with ALK gene rearrangement after detection. Of note, EML4-ALK inversion was found in seven cases, mainly appearing in the lung and soft tissue of young children. Morphologically, all the seven cases showed spindle-like cells with low mitotic activity, mild to moderate inflammatory component, and fibro-myxoid stroma, which was partially corresponding with our case.[10]

Histologically, the tumor presented as short fascicles or relatively patternless pattern, with band-like stroma and ring-shaped perivascular collagen, which was somewhat reminiscent of solitary fibrous tumor (SFT). SFT, an encapsulated and well-demarcated neoplasm, is often discovered in pleura by chance, and STAT6 is always chosen as a hallmark in diagnosis. Besides, the district with abundant myofibroblasts, in which nuclei showed mild-moderate atypia, along with collagen fascicles shared a similar pattern with well-differentiated fibrosarcoma. In addition, it was imperative for us to take the neoplasms with CD34/S100+ immunophenotype into consideration. Because the tumor being mainly composed of spindle cells with low to intermediate mitotic count and lack of necrosis, more attention should be paid to low-grade malignant peripheral nerve sheath tumor (MPNST) having CD34 and S100 coexpression, especially when the alternate pattern of cell count appears.[1] Different from conventional MPNST, our case had no relationship with neurofibromatosis type 1 and did not show SOX10 expression.

In summary, we report a novel ALK-EML4 gene fusion in CD34 and S100 coexpression spindle cell neoplasm with distinct myxoid hyaline stroma and perivascular collagen rings. The presented case not only broadened the molecular genetic spectrum of this specific group, which always related to NTRK-rearranged but also provided a rationale for targeted therapy. Being aware of unique morphologic and immunophenotypic features along with the explicit fusion is important to patients who could be treated with selective kinase inhibitors. What's more, we discussed the possible reasons for the existence of mucus-like features, which partly got rid of the stereotype between ALK and IMTs.


The authors would like to thank Dr. Du Zunguo (Department of Pathology, Huashan Hospital of Fudan University) who kindly gave financial support and Dr. Tang Feng (Department of Pathology, Huashan Hospital of Fudan University) who kindly gave technical support. The authors would like to thank Dr. Bai Qianming (Department of Pathology, Fudan University Shanghai Cancer Center) who kindly referred the NGS platform.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

   References Top

Suurmeijer AJH, Dickson BC, Swanson D, Zhang L, Sung YS, Cotzia P, et al. A novel group of spindle cell tumors defined by S100 and CD34 co-expression shows recurrent fusions involving RAF1, BRAF, and NTRK1/2 genes. Genes Chromosomes Cancer 2018;57:611-21.  Back to cited text no. 1
Davis JL, Lockwood CM, Stohr B, Boecking C, Al-Ibraheemi A, DuBois SG, et al. Expanding the spectrum of pediatric NTRK-rearranged mesenchymal tumors. Am J Surg Pathol 2019;43:435-45.  Back to cited text no. 2
Barreca A, Lasorsa E, Riera L, Machiorlatti R, Piva R, Ponzoni M, et al. Anaplastic lymphoma kinase in human cancer. J Mol Endocrinol 2011;47:R11-23.  Back to cited text no. 3
Guan J, Umapathy G, Yamazaki Y, Wolfstetter G, Mendoza P, Pfeifer K, et al. FAM150A and FAM150B are activating ligands for anaplastic lymphoma kinase. eLife 2015;4:e09811. doi: 10.7554/eLife. 09811.  Back to cited text no. 4
Palmirotta R, Quaresmini D, Lovero D, Silvestris F. ALK gene alterations in cancer: Biological aspects and therapeutic implications. Pharmacogenomics 2017;18:277-92.  Back to cited text no. 5
Bennett JA, Nardi V, Rouzbahman M, Morales-Oyarvide V, Nielsen GP, Oliva E. Inflammatory myofibroblastic tumor of the uterus: A clinicopathological, immunohistochemical, and molecular analysis of 13 cases highlighting their broad morphologic spectrum. Mod Pathol 2017;30:1489-503.  Back to cited text no. 6
Possidente L, Landriscina M, Patitucci G, Borgia L, Lalinga V, Vita G. ALK rearrangement in specific subtypes of lung adenocarcinoma: Immunophenotypic and morphological features. Med Oncol 2017;34:76.  Back to cited text no. 7
Rodig SJ, Mino-Kenudson M, Dacic S, Yeap BY, Shaw A, Barletta JA, et al. Unique clinicopathologic features characterize ALK-rearranged lung adenocarcinoma in the western population. Clin Cancer Res 2009;15:5216-23.  Back to cited text no. 8
Jokoji R, Yamasaki T, Minami S, Komuta K, Sakamaki Y, Takeuchi K, et al. Combination of morphological feature analysis and immunohistochemistry is useful for screening of EML4-ALK-positive lung adenocarcinoma. J Clin Pathol 2010;63:1066-70.  Back to cited text no. 9
Antonescu CR, Suurmeijer AJ, Zhang L, Sung YS, Jungbluth AA, Travis WD, et al. Molecular characterization of inflammatory myofibroblastic tumors with frequent ALK and ROS1 gene fusions and rare novel RET rearrangement. Am J Surg Pathol 2015;39:957-67.  Back to cited text no. 10

Correspondence Address:
Yin Wang
Department of Pathology, Huashan Hospital of Fudan University, No. 12 The Middle of Wu Lu Mu Qi Road, Shanghai - 200 040
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijpm.ijpm_621_21

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