Cellular cutaneous epithelioid hemangioma harboring the rare GATA6::FOXO1 gene fusion

Abstract

Epithelioid hemangioma (EH) is a benign vascular tumor displaying diverse histomorphologies. Among these, one EH subtype comprises cellular sheets of atypical epithelioid cells, posing potential challenges in distinguishing it from malignant vascular lesions. In this case report, we present a cutaneous cellular epithelioid hemangioma that carries the rare GATA6::FOXO1 gene fusion, a recent discovery. Our aim is to provide an updated insight into the evolving knowledge of epithelioid hemangiomas while delving into the histologic and molecular characteristics of the primary differential diagnoses.

Introduction

Epithelioid hemangioma (EH) is a benign vascular neoplasm typically affecting young adults. It most frequently occurs in the head and neck region, followed by the distal extremities¹. While its most common location is in soft tissues, EH can also manifest in bone or intravascularly^2,3,4. When found superficially, it usually presents as a single, cutaneous, erythematous-violaceous papule or angiomatoid nodule, often asymptomatic or slightly painful⁵.

Recent genetic discoveries have led to the histological classification of EH into three categories: a) conventional EH, characterized by a well-circumscribed and lobular neoplasm with larger peripheral vessels and smaller central compressed vessels embedded in a fibromyxoid stroma. The endothelial cells exhibit typical epithelioid morphology with abundant eosinophilic cytoplasm, occasional intracytoplasmic vacuoles (blister cells), and hobnail (“tombstone”) appearance; b) angiolymphoid hyperplasia with eosinophilia (ALHE) subtype, which encompasses features of the conventional subtype along with lymphoid aggregates and eosinophils; c) cellular subtype, presenting as sheets of atypical epithelioid cells with minimal intervening stroma¹.

Diagnosing EH can be challenging at times due to its diverse histomorphologies, which can resemble other benign and malignant lesions. The cellular subtype, in particular, may exhibit nuclear pleomorphism and necrosis, leading to considerations of angiosarcoma and epithelioid hemangioendothelioma (EHE) in the differential diagnosis⁶. In such cases, molecular analysis of the tumor can be highly beneficial. In EH cases, gene fusions of FOS and FOSB are present in approximately one half to one third of cases^6,7,8. Nonetheless, diagnostic challenges can arise for the EHs that show negative results for these specific molecular alterations, as well as for the molecular changes typically found in lesions within the potential differential diagnosis.

In this report, we describe a case of cellular EH that possesses the rare and recently identified GATA6::FOXO1 gene fusion, a feature observed in a subset of EHs⁹.

Case report

A 33-year-old female presented with a painful 1.5 cm subdermal lesion on her right flank, which had been evident for approximately one year. It was punch biopsied at an outside institution and diagnosed as epithelioid hemangioendothelioma with positive, deep and lateral margins. The patient subsequently sought care at our hospital for further management. Upon physical examination, she was noted to have a pigmented lesion at the well-healed biopsy site and some mild, palpable thickening of the surrounding subcutaneous tissue. No other masses, axillary, or inguinal lymphadenopathy were palpated. A chest and pelvic computed tomography scan revealed superficial thickening over the right flank region but no deep involvement of the muscle or fascia. Mild adenopathy was also seen in her right axilla.

Review of the original punch biopsy showed a mid to deep dermal neoplasm (Figure 1A) composed of clusters of epithelioid cells with moderate amounts of eosinophilic to clear cytoplasm and scattered intracytoplasmic vacuolation (Figure 1, B and C). True vascular formation was also evident (Figure 1D and 2A). Notably, no mitoses or necrosis were observed. By immunohistochemistry, the tumor was positive for CD31, CD34, and ERG (Figure 2 B, C, and D, respectively) supporting its endothelial lineage. CD68 highlighted background histiocytes, whereas CAMTA1 and TFE3 were negative. Subsequent molecular testing utilizing Anchored Multiplex PCR targeting 129 cancer-related genes (MSK Archer Solid) detected a GATA6::FOXO1 gene fusion between GATA6 exon 6 (NM_005257) and FOXO1 exon 2 (NM_002015) (Figure 3). Targeted DNA sequencing (IMPACT Solid) did not detect any somatic alterations. The overall findings resulted in a diagnosis of epithelioid hemangioma.

Figure 1.

(A) Low-power magnification shows a dense mid to deep dermal lesion that spares the superficial dermis and epidermis (H&E 10x). (B,C) Higher power magnification shows a proliferation of epithelioid cells with extravasated red blood cells arranged in sheets and vaguely lobular and focally spindle configuration with no well-formed vascular spaces. The cells have moderate to abundant eosinophilic cytoplasm (H&E 50x and 100x). (D) High-power shows intracytoplasmic vacuolation and what appears to be true vascular spaces (H&E 200x).

Figure 2.

(A) High-power of the lesion shows epithelioid cells with moderate to abundant eosinophilic cytoplasm, intracytoplasmic vacuolation and true vascular spaces. The nuclei appear predominantly vesicular with prominent nucleoli (H&E 400x). By immunohistochemistry, the lesional cells show membranous positivity for CD31 (B) and CD34 (C), and nuclear positivity for ERG (D), supporting their endothelial lineage.

Figure 3.

Schematic illustration of the gene structure and transcript sequence of the GATA6::FOXO1 fusion product by MSK-Fusion. The GATA6::FOXO1 fusion leads to an in-frame fusion protein consisting of exons 1–6 of GATA6 and exons 2–3 of FOXO1. The retained protein domains [Zinc Finger (ZnF) of GATA6 and forkhead (FD) of FOXO1] are depicted.

The patient underwent a re-excision in January 2023, which showed a focus of residual tumor with negative margins. The mild adenopathy in the right axilla was interpreted as reactive. The patient has no local recurrence or distant disease as of her follow up CT scan 6 months post-surgery.

Discussion

Molecularly, between one third to one half of EHs are characterized by the presence of FOSB or FOS gene fusions^6,8. This alteration holds particular clinical significance when dealing with the cellular subtype of EH, as it can closely resemble malignant counterparts described earlier. Approximately 20% of cellular subtypes exhibit ZFP36::FOSB and WWTR1::FOSB fusions⁷, while about 50% of cellular cases display FOS rearrangements, including FOS::VIM (documented in intraosseous EHs), FOS::MBNL1, FOS::lincRNA, and FOS-unknown fusions⁵. Interestingly, none of these FOS fusions result in the expression of a chimeric protein. Instead, they introduce a stop codon at exon 4 of FOS, leading to the truncation of the FOS protein⁵. Immunohistochemically, FOSB has been shown to possess a 95% specificity for distinguishing EH from its mimics¹. However, its sensitivity varies, and one study has examined FOSB sensitivity based on EH histologic subtype. It reported a sensitivity of 75% for the conventional subtype, 100% for the ALHE subtype, but only 10% for the cellular subtype¹⁰. In a different study, FOSB had a sensitivity of 60% for the cellular subtype, while FOS immunohistochemistry had a sensitivity of 47% for the conventional type, 40% for ALHE, and 33% for the cellular subtype¹¹. Co-expression of both FOS and FOSB was seen in 37% of cases (n=17/45)¹¹. Anatomically, it’s worth noting that FOS fusions are most commonly observed in EH lesions that originate intraosseously and are rarely seen in lesions arising in the head and neck region⁶. Additionally, FOSB is more commonly associated with penile lesions⁷.

A novel GATA6::FOXO1 fusion was recently identified by Antonescu et al. in an index case, followed by a series of 5 out of 28 EHs (18%) that were negative for FOS and FOSB fusions⁹. These cases exhibited a diverse range of locations, including the dura, nasopharynx, cheek, back, and leg. Notably, the cheek and back lesions were cutaneous, and the leg lesion was subcutaneous. Four of these five lesions were excised, and one was biopsied and followed by serial imaging. Microscopically, all except one case displayed a biphasic architectural pattern consisting of well-formed vascular channels and solid sheets of epithelioid cells. These cells exhibited varying degrees of cytologic atypia, nuclear enlargement, and prominent nucleoli. One case notably showed an absence of vasoformation. In the index case, the GATA6 (NM_005257) exon 6 was fused to FOXO1 (NM_002015) exon 2, while the remaining cases were confirmed to have FOXO1 rearrangement by FISH break-apart assay, as well as colocalization with GATA6 by FISH fusion assay. Importantly, two of these five cases had available follow-up information and did not exhibit evidence of recurrence, metastases, or rapid growth after six months and three years respectively; the case that was biopsied had minimal growth from 2.4 to 3.0 cm over a four-year period⁹. Our case aligns with the clinical and morphologic spectrum of the GATA6::FOXO1-fused EH cases described by Antonescu et al.⁹.

In order to better understand this novel gene fusion, it may be helpful to understand the known functions of GATA6 and FOXO1 and their role in neoplasia. GATA6 is a member of the GATA zinc finger transcription factors located on chromosome 18 (q11.1~q11.2). It is expressed in vascular smooth muscle cells, embryonic endoderm, mesoderm, and other tissues⁹. Its significance extends to the early development of numerous human organs¹². In the context of smooth muscle, it plays a role in inhibiting myocyte proliferation while promoting contraction¹³. The role of GATA6 in neoplastic conditions remains complex and varies among different cancer types⁹. It is proposed to have both oncogenic and tumor suppressive functions. GATA6 has been found to be overexpressed in various carcinomas, such as esophageal, gastric, colorectal adenocarcinomas, ovarian, breast carcinomas, and cutaneous T cell lymphomas¹². Notably, the GATA6::FOXO1 novel fusion recently reported in EH represents the first documented case showing GATA6 involvement in vascular neoplasia, adding to the complexity of its role in different tumor types⁹.

FOXO1 belongs to the forkhead box O (FOXO) transcription factor family, which plays crucial roles in regulating various cellular processes, including cellular homeostasis, the cell cycle, apoptosis, gluconeogenesis, stem cell maintenance, cellular life span, and immune functions^9,14. In animal models, FOXO proteins have demonstrated tumor-suppressive functions. Genetic knockout of somatic FOXOs in mice resulted in spontaneous tumor formation, including thymic lymphomas and hemangiomas¹⁵. Another study showed that FOXO knockout mice developed abnormal vasculature and widespread hemangiomas¹⁶. FOXO1 is involved in various human neoplasms including PAX3/7::FOXO1 in alveolar rhabdomyosarcoma and acute myeloid leukemia⁹. Additional types of rhabdomyosarcomas with unique FOXO1 fusions have also been reported, including a recent case report of a widely metastatic rhabdomyosarcoma with epithelioid features found to have a novel NSD3::FOXO1 fusion¹⁷ and a small series of three deep, paraspinal, well-differentiated rhabdomyosarcomas with SRF::FOXO1 and SRF::NCOA1 fusions¹⁸. There are also case reports of myoepithelioma-like hyalinizing epithelioid tumor found to have OGT::FOXO fusions including fusions with FOXO1 and FOXO3^19,20. Furthermore, there are rare cases of biphenotypic sinonasal sarcoma harboring PAX3::FOXO1 fusions (2% and 7% in a series of 41 and 44 cases, respectively), which is usually characterized in approximately 90% of cases by a PAX3::MAML3 fusion^21,22. Antonescu et al. reported that their novel GATA6::FOXO1 fusion identified in a subset of EHs represents the first vascular neoplasm involving a FOXO1 fusion⁹. The novel GATA6::FOXO1 fusion codes for a fusion protein that is reported to have full function of all domains of the GATA6 protein, whereas the FOXO1 protein portion is truncated⁹.

Morphologically, the differential diagnosis of our lesion includes the malignant entities of epithelioid hemangioendothelioma (EHE) and angiosarcoma. EHE is a vascular neoplasm that primarily affects young to middle-aged adults in various anatomical sites¹. It is characterized by epithelioid and spindle-shaped cells with eosinophilic cytoplasm, often arranged singly, in cords, and trabeculae within a myxohyaline stroma¹. Some cells may contain intracytoplasmic vacuoles, often referred to as blister cells. Importantly, EHE is diffusely positive for endothelial markers such as CD31 and ERG. In approximately 85% of cases, a reciprocal t(1;3)(p36.3;q25) translocation leads to a WWTR1::CAMTA1 gene fusion, resulting in the expression of a chimeric protein, while approximately 5% of cases harbor a YAP1::TFE3 gene fusion¹. The latter typically exhibits distinctive morphologic features including nesting, vasoformation, large epithelioid cells with abundant eosinophilic cytoplasm, and lack of myxohyaline stroma¹. Highly sensitive immunohistochemical stains are available for both CAMTA1 and TFE3 chimeric proteins; in one study, only 3% of EHE tumors (2 out of 59 cases) were negative for both markers²³. Morphologically, our case mimicked an EHE with the alternative YAP1::TFE3 gene fusion more closely than the one with classic histology. Although CD31 and ERG were positive, CAMTA1 and TFE3 stains were negative, and the corresponding gene fusions were not detected.

Cutaneous angiosarcomas typically originate in the dermis and commonly exhibit two distinct morphological patterns: one characterized by slit-like vascular spaces containing endothelial cells with hyperchromatic, atypical nuclei, and the other showing a poorly differentiated appearance composed of epithelioid and spindle cells¹. While the latter description could potentially apply to our lesion, it’s crucial to note that cutaneous angiosarcomas most frequently develop on sun-damaged skin, particularly on the face and scalp¹. These tumors are most commonly seen in older men, with a median age range between 60 and 71 years^1,24. Given the age of the patient, the absence of a history of radiation exposure, the lack of significant cytologic atypia and the presence of the GATA6::FOXO1 fusion, angiosarcoma becomes a less likely diagnosis in this case.

A benign diagnostic consideration is cutaneous epithelioid angiomatous nodule (CEAN), first described in 2004 by Brenn and Fletcher as an erythematous to bluish papule or nodule predominantly located on the trunk and extremities in younger adults²⁵. While CEAN may share histologic similarities with EH, it typically resides in the superficial dermis and rarely extends to the subcutaneous tissue²⁵. CEAN is more vasoformative and rarely displays a solid cellular configuration. Some argue that CEAN and EH may represent different spectrums of the same entity^26,27. In a series of seven vascular lesions initially diagnosed as CEAN, five exhibited similar morphology to conventional EH and all showing FOSB immunohistochemical expression²⁷. The remaining two lesions resembled cellular EH; one demonstrated FOS rearrangement by FISH, while the other exhibited c-FOS immunohistochemical expression. Given the mid to deep dermal localization and the unique GATA6::FOXO1 fusion, our case is best classified as cellular EH. Lastly, a unique cutaneous epithelioid vascular tumor harboring a TMP3::ALK fusion was very recently published, which may fall within the spectrum of epithelioid hemangioma²⁸.

In summary, we report a case of cellular epithelioid hemangioma harboring a rare GATA6::FOXO1 fusion. This fusion has recently been identified in a subset of EHs that are negative for FOS and FOSB fusions. Further investigations are necessary to identify additional distinct molecular alterations in cellular EHs, enabling a more precise characterization of this heterogeneous subtype and facilitating its differentiation from malignant mimics.