Pan-Trk immunoexpression in a superficial malignant ossifying fibromyxoid tumor with ZC3H7B-BCOR fusion: A potential obfuscating factor in the era of targeted therapy

A potential conundrum in dermatopathology: molecularly confirmed superficial ossifying fibromyxoid tumors with unusual histomorphologic findings and a novel fusion

Ossifying fibromyxoid tumor (OFMT) is a rare soft tissue neoplasm of uncertain histogenesis, primarily arising in subcutaneous tissues of the extremities, head and neck, or trunk. Most cases present as well-circumscribed masses with a characteristic morphologic appearance, comprising cytologically bland ovoid cells with fibromyxoid stroma, a peripheral rim of metaplastic bone, and lobulated architecture. Nevertheless, tumors displaying unusual morphologic characteristics pose significant diagnostic challenges, requiring the detection of a pathogenic fusion for a definitive diagnosis. The majority of OFMTs exhibits PHF1 gene rearrangements. Herein, we present six cases of molecularly confirmed OFMTs with uncommon histomorphologic features, including the absence of myxoid stroma, extensive chondroid differentiation, prominent clear cell morphology, collagen entrapment, interdigitating fibrocollagenous and fibromyxoid stromal elements, and conspicuous red blood cell extravasation. One case harbored a novel fusion (EPC1::SUZ12). This study emphasizes the broad range of morphologic manifestations that can be encountered in OFMT and the crucial role of molecular testing in establishing a conclusive diagnosis in such cases.

When molecular outsmarts morphology: Malignant ossifying fibromyxoid tumors masquerading as osteosarcomas, including a novel CREBZF::PHF1 fusion

We present two cases of malignant ossifying fibromyxoid tumor (OFMT) which eluded diagnosis due to compelling clinicopathologic mimicry, compounded by similarly elusive underlying molecular drivers. The first is of a clavicle mass in a 69 year-old female, which histologically showed an infiltrative nested and trabeculated proliferation of monomorphic cells giving rise to scattered spicules of immature woven bone. Excepting SATB2 positivity, the lesion showed an inconclusive immunoprofile which along with negative PHF1 FISH led to an initial diagnosis of high-grade osteosarcoma. Next generation sequencing (NGS) revealed a particularly rare CREBBP::BCORL1 fusion. The second illustrates the peculiar presentation of a dural-based mass in a 52 year-old female who presented with neurologic dyscrasias. Sections showed a sheeted monotonous proliferation of ovoid to spindle cells, but in contrast to Case #1, the tumor contained an exuberance of reticular osteoid and woven bone deposition mimicking malignant osteogenic differentiation. NGS showed a novel CREBZF::PHF1 fusion. Both tumors recurred locally less than 1 year post-operatively. As such we reiterate that careful morphologic examination is axiomatic to any diagnosis in our discipline, but this paradigm must shift to recognize that molecular diagnostics can provide closure where traditional tools have notable limitations.

High-grade endometrial stromal sarcoma-like' sarcoma in male: Does it exist? A case report and review of the literature

We report an exceptional case of an undifferentiated round and spindle cell sarcoma, occurring in the periprostatic region of a 54-year-old male, with a 'high-grade endometrial stromal sarcoma-like' (HG-ESS) morphology and harboring a ZC3H7B::BCOR gene fusion identified by RNA-based next-generation sequencing. In this report, we describe the striking overlap of morphologic, immunohistochemical and molecular features of this current case and previously reported similar cases with ZC3H7B::BCOR fusion-positive HG-ESS, and discuss the differential diagnosis and possible pathogenesis of this unusual entity.