ALK Rearrangement and Overexpression in an Unusual Cutaneous Epithelioid Tumor With a Peculiar Whorled “Perineurioma-like” Growth Pattern: Epithelioid Fibrous Histiocytoma

Epithelioid Fibrous Histiocytoma Is on a Continuum With Superficial ALK-rearranged Myxoid Spindle Cell Neoplasm: A Clinicopathologic Series of 35 Cases Including Alternate RET and NTRK3 Fusions

Anaplastic lymphoma kinase (ALK) rearrangements drive most examples of epithelioid fibrous histiocytoma (EFH) and have been reported in an emerging family of receptor tyrosine kinase (RTK) fusion-positive mesenchymal neoplasms, including superficial ones described under the rubric of "superficial ALK-rearranged myxoid spindle cell neoplasm" (SAMS). Here, we describe 35 superficial tumors with SAMS morphology, which occurred in 18 females (51%) and 17 males at a median age at presentation of 39 years (range: 6 to 82 y). Most tumors occurred on the lower extremity (25 tumors; 71%), followed by upper extremity (5; 14%), trunk (3; 9%), and face (2; 6%). Nine tumors were reported to have grown slowly before presentation, including >10 years in 2 cases. Tumors occurred primarily in the dermis (32 tumors; 91%) or subcutis (3; 9%); 8 dermal tumors extended into the subcutis. Median tumor size was 1.3 cm (range: 0.5 to 8.0 cm). Clinical follow-up was available for 12 patients (34%; range: 2 mo to 21 y; median: 2.7 y), none of whom experienced metastasis. One incompletely resected tumor recurred locally at 19 months, and no other patients experienced recurrence. Histologically, tumors were characterized by bland spindle-to-ovoid cells showing whorled growth and myxoid-to-collagenous stroma. Recurrent features included an epidermal collarette (19/30; 63%), perivascular hyalinization (20/35; 57%), amianthoid collagen (14/35; 40%), and metaplastic ossification (2/35; 6%). Immunohistochemistry (IHC) demonstrated expression of ALK (24/31; 77%), CD34 (15/21; 71%), EMA (17/28; 61%), and S-100 (9/32; 28%). Eleven tumors showed hybrid morphologic features between EFH and SAMS; 9 of them (82%) showed cytomorphology typical of EFH but with whorled growth, myxoid stroma, and/or regions of spindle cell morphology. Two hybrid tumors showed sharp transitions between a region characteristic of EFH and a region characteristic of SAMS, with a concomitant sharp transition in EMA, CD34, and S-100 expression by IHC. Sequencing revealed ALK fusions in 15 of 19 tumors: 2 each with fusion partners FLNA, SQSTM1, and VCL, and 1 each with COL1A2, DCTN1, EML4, FXR1, MPRIP, PLEKHH2, PRKAR1A, SPECC1L, and TLN2. Thirteen of 14 ALK-rearranged tumors expressed ALK by IHC. Three tumors negative for ALK fusions instead harbored alternate RTK fusions (NCOA4::RET, TRIM27::RET, and VIM::NTRK3), and 1 tumor was negative for RTK alterations. CDKN2A/B deletions were found in 2 tumors with ALK fusions and both tumors with RET fusions. SAMS is on a morphologic and molecular genetic spectrum with EFH, with a similar body site distribution, frequent clinical presentation as an exophytic skin tumor, and invariably benign outcomes; we conclude that SAMS should be considered a histologic variant of EFH. Some morphologically typical examples harbor alternate RET and NTRK3 fusions, such that SAMS is not an appropriate designation for this morphologic class; instead, to highlight the clinicopathologic similarities to EFH, we propose the diagnostic term "myxoid spindle cell variant of epithelioid fibrous histiocytoma."

Case report: Systemic presentation of ALK-positive Histiocytosis

ALK-positive Histiocytosis (ALK-HSs) is a recently identified rare clinical entity characterized by tissue histiocytic alterations associated with ALK gene rearrangement. Clinical presentations can be solitary, multifocal, or systemic (involving multiple sites and organs). Due to limited reported cases, there is inadequate understanding of this disease. This report presents a case of ALK-HSs in a 71-year-old male patient who presented with hematuria for one week. Imaging studies conducted at an external hospital showed multiple lesions in the penis, bilateral testes, back skin, and the third lumbar vertebra. Histopathological findings included spindle and histiocytic cell proliferation with mild or indistinct cellular atypia, interstitial infiltration of lymphocytes, plasma cells, foamy histiocytes, and fibrous tissue proliferation. Immunohistochemistry of the lesion cells revealed positivity for CD68, CD163, ALK1, ALK (D5F3), and Vimentin. FISH testing indicated ALK gene separation in the lesion cells. NGS testing identified the fusion genes KIF5B(NM_004521) and ALK(NM_004304) in the lesion cells. We combined the characteristics of this case with a review of the literature to enhance our understanding of this rare clinical entity.

Epithelioid Fibrous Histiocytoma With Chondroblastoma-Like Features: A Report of a Rare Entity and Discussion of Related Diagnostic Challenges

ABSTRACT

Epithelioid fibrous histiocytoma (EFH) is an uncommon benign skin lesion. It is distinct from FH by virtue of its recurrent anaplastic lymphoma kinase (ALK) gene rearrangements and immunohistochemical expression of ALK protein. It often poses a challenge in interpretation. Clinically, it is characterized by a flesh-colored papule/nodule on an extremity of a young to middle-aged individual. Microscopically, it is represented by a circumscribed dermal papule/nodule composed of sheets of plump epithelioid cells, forming whorled aggregates around numerous intralesional vessels. Immunohistochemistry, notably ALK positivity and relevant negative stains, serves to distinguish EFH from its morphological mimics. Rare examples of chondroblastoma-like EFH and EFH with osseous metaplasia are recorded in the literature. Our case is of a 58-year-old man who attended an oculoplastic surgeon because of an exophytic cutaneous nodule on the right upper eyelid. The lesion was excised. Microscopically, it displayed morphological and immunohistochemical features of EFH. Of interest, discrete foci of chondro-osseous change, including chondroblastoma-like pericellular calcification, osteoid formation, and osteoclast-like giant cells, were noted throughout the lesion. A diagnosis of EFH with chondroblastoma-like features was made. Of interest, the changes observed in this EFH serve to link the previously reported examples of pure chondroblastoma-like EFH and EFH with osseous metaplasia. This morphological variant of EFH adds to the existing diagnostic challenge presented by these lesions, particularly in the distinction from other calcifying tumors of the skin.

Broadening the spectrum of NTRK rearranged mesenchymal tumors and usefulness of pan-TRK immunohistochemistry for identification of NTRK fusions

Fusions involving NTRK1, NTRK2, and NTRK3 are oncogenic drivers occurring in a spectrum of mesenchymal neoplasms ranging from benign to highly malignant tumors. To gain further insights into the staining profile with the pan-TRK assay, we analyzed a large number of soft tissue sarcomas and correlated our findings with molecular testing. Additionally, we expand the spectrum of NTRK-fusion tumors by reporting a mesenchymal lesion in the lung as well as a mesenchymal skin lesion in the spectrum of benign fibrous histiocytoma with NTRK-fusion. We retrospectively reviewed soft tissue sarcomas diagnosed at the Diagnostic and Research Institute of Pathology, Medical University of Graz, between 1999 and 2019, and cases from the consultation files of one of the authors (BLA). In total, 494 cases were analyzed immunohistochemically with pan-TRK antibody (clone EPR17341, RTU, Roche/Ventana) and positive cases (defined as any cytoplasmic/nuclear staining in more than 1% of tumor cells) underwent next-generation sequencing (NGS). Immunohistochemical staining was observed in 16 (3.2%) cases. Eleven cases with focal weak and moderate cytoplasmic/membranous or focal moderate to strong nuclear staining did not harbor an NTRK-fusion (three synovial sarcomas, three leiomyosarcomas, two extraskeletal myxoid chondrosarcomas, and one each: dedifferentiated liposarcoma, pleomorphic liposarcoma, and myxofibrosarcoma). Four cases showed strong diffuse nuclear and/or cytoplasmatic staining, and one case showed diffuse, but weak cytoplasmic staining. All these cases demonstrated an NTRK-fusion (LMNA-NTRK1, IRF2BP2-NTRK1, TMB3-NTRK1, ETV6-NTRK3, RBPMS-NTRK3). Pan-TRK assay (clone EPR17341, RTU, Roche, Ventana) immunohistochemistry serves as a reliable diagnostic marker that can also be expressed in non-NTRK-rearranged mesenchymal neoplasms. It can be used as a surrogate marker for identification of NTRK fusion, nevertheless, an RNA-based NGS for detection of the specific fusion should be performed to confirm the rearrangement, if patients are undergoing targeted therapy. Additionally, we identified NTRK-fusion-positive, primary mesenchymal tumors of the lung and the skin.

Spindle cell variant of epithelioid cell histiocytoma (spindle cell histiocytoma) with ALK gene fusions: Cases series and review of the literature

BACKGROUND

Epithelioid fibrous histiocytoma (EFH) is an uncommon dermal neoplasm expressing anaplastic lymphoma kinase (ALK) protein. Rarely a histopathological variant of this entity exhibits exclusively spindle cells. We report three cases of EFH that do not completely fulfill phenotypic criteria featuring spindle cell morphology and expressing ALK protein. We also analyze the fusion partner genes rearranged with ALK in these cases.

METHODS

ALK expression and rearrangement status were evaluated by immunohistochemistry (IHC), fluorescence in situ hybridization (FISH), and next generation sequencing based gene fusion analysis.

RESULTS

Three cases, all from females between 25 and 55 years old, have been biopsied from back, left arm, and thumb. All three cases showed tumor with exclusively spindle cell morphology without any epithelioid cells. The tumor cells exhibited strong ALK expression by IHC and FISH study confirmed ALK gene rearrangement in all three cases. DCTN1-ALK fusion was identified in two cases.

CONCLUSION

EFH is not always purely epithelioid and its spindled cell variant, spindle cell histiocytoma, should be included in the differential diagnosis of superficial dermal spindled cell neoplasms. ALK immunostain is a useful diagnostic marker for this entity and further studies may be useful to investigate whether DCTN1-ALK fusion mutations are specific to EFH with spindled cell features.

ALK Gene Fusions in Epithelioid Fibrous Histiocytoma: A Study of 14 Cases, With New Histopathological Findings

Previous studies showed that ALK is often positive in epithelioid fibrous histiocytoma (EFH). Two cases of EFH with ALK gene fusions have been recorded. Our objective was to study a series of EFH to present histopathological variations of EFH, identify novel ALK gene fusions, and determine whether there is a correlation between histopathological features and particular gene. We investigated 14 cases of EFH, all ALK immunopositive. The cases were assessed histopathologically as well as for ALK and TFE-3 rearrangements using FISH and ALK gene fusions using next-generation sequencing. The analysis of the sequencing results was performed using the Archer Analysis software (v5; ArcherDX Inc). The study group consisted of 8 female and 6 male patients, ranging in age from 18 to 79 years (mean 42 years; median 37.5 years). All presented with a solitary lesion. Microscopically, most lesions were polypoid and composed of epithelioid cells with ample cytoplasm. In addition, a variable number of bi-, tri-, or multinucleated, spindled, multilobated, cells with eccentric nuclei, cells with nuclear pseudoinclusions, mucinous, and grooved cells were admixed. In 5 cases, the predominant epithelioid cell component consisted of rather small cells, whereas spindled cells dominated in 3 cases. Of these, 2 lesions were composed rather of pale eosinophilic to clear cells, occasioning a resemblance to PEComa or leiomyoma. Immunohistochemically, all cases expressed ALK and 11 were positive for TFE-3. The break apart test for ALK was positive in 11 cases, whereas specimens from the remaining 3 cases were not analyzable. ALK genes fusions were found in all but 3 cases and included SQSTM1-ALK (3), VCL-ALK (3), TMP3-ALK (2), PRKAR2A-ALK (1), MLPH-ALK (1), and EML4-ALK (1). No correlation between histological features and type of ALK fusion was found. TFE-3 break apart test was negative. It is concluded that ALK-immunopositive EFH shows ALK gene fusions that involve various protein-coding genes, implicated in a variety of biological processes. Rare variants of EFH rather consist of spindled "non-epithelioid" cells.

Epithelioid cell histiocytoma with SQSTM1-ALK fusion: a case report

Background

Epithelioid cell histiocytoma (ECH), which is also known as epithelioid benign fibrous histiocytoma, has been classified as a rare variant of fibrous histiocytoma (FH). However, the recent detection of ALK protein expression and/or ALK gene rearrangement in ECH suggests that it might be biologically different from conventional FH.

Case presentation

A 27-year-old male presented with nodule on his left foot, which had been present for 5 years. A macroscopic examination revealed an exophytic, hyperkeratotic nodule on the dorsum of the left foot. Tumorectomy was performed, and a microscopic examination showed a subepidermal lesion composed of sheets of tumor cells with oval to round nuclei and ill-defined eosinophilic cytoplasm. The tumor cells were diffusely positive for factor XIIIa and ALK, but were negative for AE1/AE3 keratin, alpha-smooth muscle actin, CD30, CD34, CD68, PU.1, melan A, MITF, and S-100 protein. ALK immunostaining showed a diffuse cytoplasmic staining pattern. ALK fluorescence in situ hybridization demonstrated break-apart signals, which was suggestive of ALK rearrangement. A 5′-rapid amplification of cDNA ends assay detected SQSTM1-ALK fusion, in which exon 5 of the SQSTM1 gene was fused to exon 20 of the ALK gene. The patient was free from recurrence and distant metastasis at the 1-year of follow-up.

Conclusion

We were able to demonstrate the SQSTM1-ALK fusion gene in ECH. Practically, detecting immunopositivity for ALK and appropriate cell-lineage markers are the key to diagnosing ECH.