Clinical Benefit From Immune Checkpoint Blockade in Sclerosing Epithelioid Fibrosarcoma: A Translocation-Associated Sarcoma

YAP1::KMT2A fusion-positive sarcoma: An emerging soft tissue tumor entity with morphological features resembling a sclerosing epithelioid fibrosarcoma

ABSTRACT

Sclerosing epithelioid fibrosarcoma (SEF) and low-grade fibromyxoid sarcoma (LGFMS) constitute a morphological continuum with certain overlapping histopathological features and MUC 4 immunopositivity. SEF is characterized by EWSR1 gene rearrangement, is relatively more aggressive and shows a limited response to chemotherapy. Lately, a subset of tumors with morphological features of SEF, but lacking MUC4 immunostaining and EWSR1 gene rearrangement have been observed. We report the first case of YAP1::KMT2A -positive sarcoma from the Indian subcontinent along with a review of similar tumors reported previously. A case of 31-year-old male presented with a 3 cm painful lump in the right suboccipital region. Histopathological examination of the excised specimen revealed a cellular tumor composed of atypical spindle and epithelioid cells, exhibiting moderate nuclear pleomorphism, arranged in cords, embedded in a dense collagenous/hyalinized stroma. By immunohistochemistry, the tumor cells were diffusely positive for cyclin D1 and negative for MUC4, desmin, myogenin, β-catenin, STAT6, myoD1, SMA, and S100P. By fluorescence in-situ hybridization, EWSR1 gene rearrangement was negative. Next-generation sequencing (NGS) revealed YAP1exon5::KMT2Aexon4 fusion. Given a positive resection margin, he underwent a revision surgery involving wide local excision of the lesion including the outer table of the occipital bone followed by image-guided radiation therapy. Over 2 years of his follow-up, the patient is alive with no evidence of recurrence. Thus, YAP1::KMT2A positive sarcomas have distinct molecular and overlapping histopathological features with SEF, with relatively less aggressive disease course. Documentation of additional similar tumors with long-term follow-up is required.

Sclerosing Epithelioid Fibrosarcoma

Sclerosing epithelioid fibrosarcoma (SEF) is a distinctive sarcoma that may arise in nearly any soft tissue site or bone. While there has been past controversy as to whether it is related to low-grade fibromyxoid sarcoma (LGFMS), it has been shown to behave far more aggressively than LGFMS. SEF has a propensity to metastasize to the lungs and bone and arise within the abdominal cavity. Histologically, it is characterized by uniform nuclei embedded in a densely collagenous stroma simulating osteoid. By immunohistochemistry, it is often strongly positive for MUC4. The majority (75%) have EWSR1 gene rearrangement, most commonly with CREB3L1 as a fusion partner, although a variety of FUS/EWSR1 and CREB3L1/CREB3L2/CREB3L3 fusions have been described in addition to others. SEF is currently recalcitrant to nearly all chemotherapy and radiation therapy.

Response to Immunotherapy in Sclerosing Epithelioid Fibrosarcoma: Case Report and Literature Review

Sclerosing epithelioid fibrosarcoma (SEF) is an extremely rare subtype of sarcoma that appears histologically low-grade yet usually has a clinically aggressive course with a high rate of local recurrence and distant metastasis. However, these recurrences and metastases often occur years after initial treatment. Metastases can be to the lung as well as extra-pulmonary sites. In this case report, we discuss a patient who developed SEF in the deep soft tissue with metastases. This patient underwent checkpoint inhibitor therapy, with disease response. Thus, SEF is a sarcoma subtype with a unique tumor biology, and immunotherapy may be a promising avenue for treatment.

Exploring the landscape of immunotherapy approaches in sarcomas

Sarcomas comprise a heterogenous group of malignancies, of more than 100 different entities, arising from mesenchymal tissue, and accounting for 1% of adult malignancies. Surgery, radiotherapy and systemic therapy constitute the therapeutic armamentarium against sarcomas, with surgical excision and conventional chemotherapy, remaining the mainstay of treatment for local and advanced disease, respectively. The prognosis for patients with metastatic disease is dismal and novel therapeutic approaches are urgently required to improve survival outcomes. Immunotherapy, is a rapidly evolving field in oncology, which has been successfully applied in multiple cancers to date. Immunomodulating antibodies, adoptive cellular therapy, cancer vaccines, and cytokines have been tested in patients with different types of sarcomas through clinical trials, pilot studies, retrospective and prospective studies. The results of these studies regarding the efficacy of different types of immunotherapies in sarcomas are conflicting, and the application of immunotherapy in daily clinical practice remains limited. Additional clinical studies are ongoing in an effort to delineate the role of immunotherapy in patients with specific sarcoma subtypes.

Mediastinal Low-Grade Fibromyxoid Sarcoma With FUS-CREB3L2 Gene Fusion

Low-grade fibromyxoid sarcoma (LGFMS) is a rare subclass of sarcoma. Histologically, they are characterized by bland-appearing fibroblastic spindle cells and are similar to sclerosing epithelioid fibrosarcoma (SEF) subtype. The standard treatment of this aggressive tumor subtype is surgical removal with wide excision in conjunction with doxorubicin chemotherapy. Due to the rarity of this disease, effective systemic therapies are lacking and patient outcomes remain poor. Herein, we report on a 50-year-old male who presented with severe shortness of breath. Subsequent imaging revealed pericardial effusion and large mediastinal mass consistent with locally advanced disease. Fine needle biopsy demonstrated malignant, Ewing-like round tumor cells. Further genetic analysis affirmed the presence of FUS-CREB3L2 gene fusion. The patient was treated with doxorubicin and survival time from the initial presentation was five months. To date, there are limited reports of this disease. Few targeted therapies or immunotherapies for LGFMS exist, and a dire need for new therapy development remains.