Superficial Acral Fibromyxoma: Report of 13 Cases With New Immunohistochemical Findings

A Case of Superficial Acral Fibromyxoma of the Index Finger

Superficial acral fibromyxoma (SAFM) is a rare, slow-growing benign soft tissue tumor that is typically asymptomatic in nature and usually affects the acral regions of the hands and feet. The majority of these lesions are subungual. Excisional biopsy is the primary treatment modality. Despite the distinct clinical and histopathological features, misidentification of this slow-growing tumor persists. This case report contributes to the existing literature by delineating the clinicopathologic features, radiographic and MRI findings, and treatment strategies of SAFM.

RB1 loss in the mesenchymal component of onychomatricoma

BACKGROUND

Onychomatricoma is a nail neoplasm that usually presents as longitudinal nail plate thickening, involving either the partial or whole nail. Histopathologically, it is characterized by deep invaginations of the proliferating nail matrix and proliferation of CD34+ and CD10+ spindle cells with collagenous to myxoid stroma. Onychomatricoma has been considered a fibroepithelial neoplasm. Recently, RB1 loss has been verified using array comparative genomic hybridization.

METHODS

This study investigated the RB1 status in onychomatricoma with morphological methods.

RESULTS

Six patients with onychomatricoma were included in the study. RB1 status was assessed using immunohistochemical staining and fluorescence in situ hybridization. Immunohistochemical staining showed that all six cases experienced RB1 loss in the mesenchymal component of onychomatricoma but not in the proliferated nail matrix. Fluorescence in situ hybridization in five cases showed a monoallelic deletion of the RB1 locus in the mesenchymal component but not in the proliferated nail matrix.

CONCLUSIONS

RB1 loss was observed only in the mesenchymal component of onychomatricoma. Our findings suggest that the proliferated nail matrix in onychomatricoma represents reactive hyperplasia of various degrees secondary to neoplastic mesenchymal proliferation. This indicates that onychomatricoma should be recognized as an RB1-deleted soft tissue neoplasm rather than a fibroepithelial neoplasm.

Onychomatricoma: a clinicopathological, immunohistochemical, and molecular study of 10 cases highlighting recurrent RB1 deletion and the potential diagnostic value of LEF-1

AIMS

Onychomatricoma (OM), an uncommon benign fibroepithelial neoplasm of the nail unit, is sometimes diagnostically challenging for clinicians and pathologists. OM consistently expresses CD34, but no specific immunohistohemical markers or recurrent genetic alterations have been identified to date. Recent studies have suggested that Wnt signalling is a key molecular characteristic of OM.

METHODS AND RESULTS

Ten cases were analysed: four classical OM including two with pleomorphic cells; two superficial acral fibromyxoma-like variants of OM; three micropapilliferum variants of OM including one with pleomorphic cells; and one proliferating variant of OM. Immunohistochemically, the spindle cells were positive with CD34 (n = 10) and CD99 (n = 1), with focal reactivity for CD10 (n = 5). The epithelial component of the tumours expressed immunopositivity for LEF-1. Using array comparative genomic hybridization (aCGH), we demonstrated that all OM, including its variants that were tested (n = 8), harboured a few copy number alterations with losses of whole or part of chromosome 13 including the RB1 gene (n = 8) and chromosome 16 (n = 6).

CONCLUSION

We report a recurrent loss of RB1 (13q) as a possible driver molecular event in OM indicating a relationship between OM and other lesions of the spectrum of the so-called '13q/RB1' family of tumours. We did not identify a role for the Wnt/beta-catenin signalling pathway, as has been proposed in a recent study. LEF-1 could be a potential sensitive and specific marker of OM and should be used in the differential diagnosis between OM, superficial acral fibromyxoma, and the CD34-positive fibrosing family of tumours.

Acral fibromyxoma: a rare plantar nodule

Acral fibromyxomas are benign tumours ranging in size between 0.6 and 5 cm, commonly found around the nailbed. The often asymptomatic presentation of acral fibromyxomas means that there is often a delay in their diagnosis and subsequent treatment. The objective of this paper is to present the unique case of a fibromyxoma present in the acral region, as well as a review of the literature.

A Rare Case of Myxochondroid Metaplasia of the Plantar Foot With Review of Histopathological Mimics

ABSTRACT

Chondromyxoid metaplasia can rarely lead to the formation of a distinctive tumor-like proliferation in the plantar foot. This is thought to represent a reactive or reparative process, possibly due to chronic trauma. For the unwary dermatopathologist, this could represent a diagnostic challenge. Herein, we review the clinical, histopathological, and molecular presentation of an athletic 17-year-old boy with a soft tissue mass arising in the right plantar foot. Microscopic examination showed a relatively circumscribed proliferation of spindle cells with abundant chondromyxoid stroma, hyalinization, and diffuse ERG reactivity. We also review characteristics of this entity that help differentiate it from clinical and histopathologic mimics and postulate possible links with soft tissue chondromas and immature chondroid choristoma.

EWSR1-SMAD3 rearranged fibroblastic tumor: Case series and review

We report the largest series to date (N = 6) of EWSR1-SMAD3 rearranged fibroblastic tumor. Initially described in 2018, the tumor features a marked female predominance (F:M, 5:1, mean age 44-years, median age 45.5 years; range 27-57), with most cases (5/6, 83%) arising in acral locations (4 on foot/toe, 1 on hand). One case presented on the lower extremity. The lesions presented as nodules and were composed of short, variably cellular, intersecting fascicles of uniform spindled cells in a collagenous to myxoid stroma. In four cases, the tumor abutted the epidermis without a grenz zone. In one case, there was an abrupt transition to a central, acellular hyalinized area. Two other cases had admixed smaller collagenous areas, reminiscent of collagen rosettes. One had a concentric arrangement of tumor cells around blood vessels. Mitotic activity was low (<1/10 HPFs). All were positive for ERG by immunohistochemistry and negative for CD34 (6/6). An EWSR1-SMAD3 fusion was identified in three cases tested by next-generation sequencing (3/3). Rearrangement of EWSR1 by fluorescence in situ hybridization was showed in 1/1 case. Our series reaffirms prior findings and expands the known histopathologic spectrum of this emerging entity.

Cellular Digital Fibroma: A Comprehensive Review of a CD34-Positive Acral Lesion of the Distal Fingers and Toes

Cellular digital fibroma is a benign fibrous lesion that typically occurred on either a finger or a toe. Cellular digital fibroma was introduced as a distinctive cluster of differentiation 34 (CD34)-positive lesion in July 2005. Cellular digital fibroma has been described in 20 patients: 12 men and 8 women. The patients ranged in age from 27 to 83 years old (median, 52 years old) at diagnosis. The tumor had been present from 2 months to 2 years (median, 11 months) prior to seeking medical attention. The cellular digital fibroma was usually slowly growing and asymptomatic; there has been no prior history of trauma at the tumor site. The lesion typically presented as either an erythematous or a flesh-colored, solitary papule of 5 mm or smaller. It frequently occurred on either the dorsal, lateral or ventral side of a digit. Yet, some of the lesions were located on the nail fold of the digit. Cellular digital fibroma shows a prominent cellular proliferation of spindle-shaped fibroblasts, without any atypia or mitoses, that extends from the papillary into the upper reticular dermis; diffuse and strongly positive CD34 staining is present throughout the entire tumor. There is no erosion by the tumor of the bony phalanx. Other acral tumors, such as superficial acral fibromyxoma (which also has diffuse strongly positive CD34 staining) and acquired digital fibrokeratoma (which is either CD34-negative or only focal CD34 positive), are in the clinical and pathologic differential diagnosis of cellular digital fibroma. Conservative complete excision is the treatment of cellular digital fibroma; however, even for tumors that have only been partially removed during biopsy, recurrence has not been observed. In conclusion, cellular digital fibroma is a unique CD34-positive acral lesion of the distal fingers and toes whose diagnosis requires correlation of the clinical morphology and the pathologic features of the tumor.

Superficial acral fibromyxoma in the heel with new vascular features on dermoscopy

Superficial acral fibromyxoma (SAFM) is an uncommon mesenchymal soft tissue tumor with a predilection for the acral extremites and nail bed involvement. SAFM is diagnosed with clinicopathological and immunohistochemical examination. Awareness of this rare tumor is important because of amounts of benign and malignant neoplasms. We report a case of SAFM in a rare localization in the heel with a new finding on dermoscopy.