Acral Fibrochondromyxoid Tumor Presenting as Enlarging Nodule Involving the Distal Fingertip and Hyponychium: A Case Report

Abstract

An acral fibrochondromyxoid tumor is a newly described type of benign soft tissue neoplasm that presents as a single nodular lesion on a finger or toe. There has only been one previous report on this tumor, a case series that described the initial pathologic and clinical findings; however, details on clinical history, physical examination, and outcome are unknown. In this report, we describe a case of a 39-year-old male who presented with a painful enlarging mass involving the distal right 3rd finger and hyponychium. Punch biopsy was performed and the lesion was identified as an acral fibrochondromyxoid tumor on microscopic examination. X-ray showed no bony involvement. The tumor was successfully excised with complete resolution of pain symptoms. We discuss the clinical features and immunohistochemistry findings of our case in the context of the current limited knowledge about this very rare tumor.

Introduction

Acral fibrochondromyxoid tumors are a newly described type of benign acral soft tissue neoplasm that present as a single nodular lesion on a finger or toe. There has been one case series describing the pathology of this type of tumor, but little is currently known about their clinical history, physical examination, and outcome. Additionally, involvement of the nail unit has never previously been described. The CARE Checklist has been completed by the authors for this case report, attached as online supplementary material (for all online suppl. material, see www.karger.com/doi/10.1159/000529568).

Case Report

A 39-year-old male presented for evaluation of a mass involving the distal right 3rd finger and fingernail for 18 months. It was not painful at baseline, but he reported pain in both hot and cold and severe, shooting pain with pressure. Notably, he was a clothing tailor for over a decade and wore an open-tip thimble on this digit daily with occasional needle pricks but no other trauma. He was taking no medications and had no significant past medical history. Family history was significant for smoking-associated lung cancer in his maternal grandmother.

Physical examination revealed a tender lichenified flesh-colored nodule involving the distal right 3rd finger and hyponychium (Fig. 1). X-ray was unremarkable for any osseous abnormalities. Differential diagnosis included callus, verruca vulgaris, glomus tumor, inclusion cyst, chondroma, and neuroma. A punch biopsy was performed for diagnosis.

Fig. 1.

Tender flesh-colored nodule with lichenification of the right 3rd finger hyponychium/distal tip.

On microscopic examination, the digit/nail specimen showed a circumscribed neoplasm with a distinctly myxomatous background largely demarcated from the uninvolved dermis/epidermis by a border of fibrosis and neovascularization. Suspended in this sea of basophilic material were singly disposed epithelioid round-to-spindle-appearing cells. The polygonal-to-round cells had round-to-oval nuclei and/or reniform nuclei. The cells had vacuolated cytoplasms. There was a minor cell population which was more spindled with elongated nuclei. Significant nuclear atypia was absent. Cytoplasm of both the rounded and spindled cells was abundant and eosinophilic (Fig. 2).

Fig. 2.

a Circumscribed neoplasm with myxomatous background matrix (H&E. ×20). b Suspended in basophilic material were singly disposed epithelioid round cells arranged in single cells and cords (H&E. ×200). c Distinct monocytoid cells, with oval-reniform-shaped nuclei eccentrically disposed with lightly eosinophilic cytoplasm (H&E. ×400).

The tumor cells showed positive staining for CD34, epithelial membrane antigen (EMA), collagen IV, factor 13A, and nuclear staining for p63, without significant staining for S100, SOX-10, CD31, CD68, calponin, anaplastic lymphoma kinase, GFAP, cytokeratin, and caldesmon. There was no STAT6 nuclear staining. INI-1 did not show significant nuclear staining of the neoplastic cellular elements. Only rare cells exhibited nuclear staining for Ki-67 (Fig. 3). Histological findings were overall most consistent with the recently described entity of an acral fibrochondromyxoid tumor.

Fig. 3.

Tumor cells stained positively for EMA (DAB. ×200), CD34 (DAB. ×200), and P63 (DAB. ×200).

Discussion

Acral fibrochondromyxoid tumor is a newly described neoplasm exclusively involving the fingers and toes. Prior to our case, there was only a single case series of 10 acral fibrochondromyxoid tumors, with median age 42 years, slight male predominance (7:3), and 70% involving the fingers. The majority of these cases were not painful (70%). Of the finger cases, 2 localized to the metacarpophalangeal joint, 2 in the proximal phalange, 0 in the intermediate phalange, 2 in the distal phalange, and 1 in unknown location (Table 1) [1].

Table 1.

Comparison of the findings in this case to the acral fibrochondromyxoid tumors reported in the previous case series

Characteristics	Case tumor	Previous case series (10 cases) [1]
Age, years	39	Median of 42 (20–64)
Gender	Male	70% male (7/10)
Location	3rd finger	7/10 on fingers
Painful	Yes	30% (3/10)
Bone involvement	None	50% (5/10)
Microscopic findings	Relatively uniform population of small ovoid-spindle cells, including cells with a reniform appearance, in an abundant background of fibrous and chondroid myxoid stroma
Immunohistochemistry
CD34	+	+ (10/10)
EMA	+	− (9/10)
Collagen IV	+	Unknown
Factor 13A	+	Unknown
p63	+	− (8/10)
ERG	+	+ (9/10)
SMA	Focal	− (10/10)
S100	−	− (5/10)
SOX-10	−	− (10/10)
CD31	−	Not reported
CD68	−	Not reported
Calponin	−	Not reported
Anaplastic lymphoma kinase	−	Unknown
GFAP	−	Unknown
Cytokeratin	−	Unknown
Caldesmon	−	Unknown
STAT6	−	Unknown
INI-1	−	Unknown
Ki-67	Rare cells	Rare cells

Radiologic findings of acral fibrochondromyxoid tumors have not been well studied. In one previous case, X-ray showed focal soft tissue fullness adjacent to the phalanx with saucerization of underlying cortical bone. Computed tomography and magnetic resonance imaging confirmed a well-circumscribed soft tissue mass with chronic pressure bone erosion [2]. Radiologic imaging for the other cases showed that 50% invaded into adjacent bone.

On histology, an acral fibrochondromyxoid tumor is characterized by a proliferation of a relatively uniform population of small ovoid-spindle cells, including cells with a reniform appearance. A key feature is an abundant background of fibrous and chondroid myxoid stroma. The histopathological differential diagnosis includes soft-tissue chondroma, chondromyxoid fibroma, myoepithelioma/parachordoma, chondroid myxoid variant of epithelioid histiocytoma, and superficial acral fibromyxoma. RNA sequencing identified a defining THBS1-ADGFR5 gene fusion in all 10 cases in the reported series. This fusion was never previously reported with other neoplasms and was not found in a control cohort that included most tumors in the histological differential. On immunohistochemistry, the majority of these tumors expressed CD34 (100%), ERG (90%), and SOX9 (70%). Half of the previously reported cases expressed S100 but usually no expression of SMA (0%), SOX10 (0%), EMA (10%), or p63 (20%) [1]. Therefore, some immunohistochemical findings in our case were uncommon in previous cases, namely, significant reactivity for EMA and nuclear staining for p63. However, since so few cases have been reported, no immunohistochemistry profile can be considered diagnostic for this neoplasm. Therefore, these differences did not change the diagnosis as the overall clinicopathological picture was most consistent with an acral fibrochondromyxoid tumor. Further reports of immunohistochemistry profiles from other AFCM tumors in the future will help to more accurately elucidate the typical diagnostic profile of this neoplasm.

Our case also showed significant staining for factor 13A and type IV collagen, which had not been examined in the previous cases. There was also a lack of INI-1 immunostaining, with unclear significance, given that the overall histology was not consistent with an epithelioid sarcoma [3].

There are distinct histopathologic features that differentiate this entity from the other etiologies on the differential diagnosis. Superficial acral fibromyxomas commonly occur as soft-tissue tumors in the subungual/periungual region but histologically show stellate-shaped fibroblast-like cells in a storiform pattern, which is not seen in acral fibrochondromyxoid tumors [4]. Soft tissue chondromas contain a matrix of hyaline cartilage with mature chondrocytes, as compared to the distinctive immature hyalinized, myxoid, and chondroid matrix observed here [5]. Conversely, myoepitheliomas (parachordomas) may have a similar hyalinized, myxoid, and chondroid matrix but are characteristically positive for cytokeratin, S-100, and calponin, all of which were negative in this case [6]. Chondroid myxoid variants of epithelioid histiocytomas are also positive for EMA and factor 13A, similar to this case; however, chondroid myxoid variants are generally not lobulated and are invariably anaplastic lymphoma kinase positive, in contrast to the negative staining result in this case [7].

All 10 previous cases were treated with marginal resection, with none requiring digit amputation. Eight cases were primary tumors with no recurrences (median follow-up 17.5 months, range 3–42 months). Two cases were recurrent tumors after unknown time frame from original excision. Both were re-resected with no additional recurrences reported (1 lost to follow-up; 1 with no recurrence at 14 months). Our patient was referred to hand surgery for resection of the remaining tumor. The patient underwent a successful excision of the tumor with no complications. At 2-month follow-up, the patient had no evidence of recurrence and reported complete resolution in previous pain symptoms.

Acral fibrochondromyxoid tumor is a very rare digit neoplasm that cannot be diagnosed by clinical examination or imaging alone. These tumors may appear at the distal finger in association with the nail unit and thus may be inaccurately diagnosed clinically as a subungual glomus tumor or wart. Any nodular distortion of the nail apparatus should prompt concern regarding a neoplastic process and definitive evaluation with a biopsy.

Statement of Ethics

Since this study was a case report, ethics approval was not required by the Weill Cornell Medicine Institutional Review Board. Written informed consent was obtained from the patient for publication of this case report and any accompanying images.

Conflict of Interest Statement

Rhiannon Christine Miller, Dr. Laura E. Melnick, and Dr. Cynthia M. Magro have no conflicts of interest. Dr. Shari R. Lipner has served as a consultant for ortho-dermatologics, Verrica, Hexima, Belle Torus, and Hoth Therapeutics.

Funding Sources

This article has no funding source.

Author Contributions

Rhiannon Christine Miller contributed to chart review, literature review, consenting the patient, and writing/revision of the manuscript. Dr. Cynthia M. Magro contributed to diagnosis/treatment of the patient, histopathologic testing and images, literature review, and writing/revision of the manuscript. Dr. Laura E. Melnick contributed to diagnosis/treatment of the patient, chart review, and revision of the manuscript. Dr. Shari R. Lipner contributed to the diagnosis/treatment of the patient, chart review, literature review, and writing/revision of the manuscript.

Funding Statement

This article has no funding source.

Data Availability Statement

All data generated or analyzed during this study are included in this article and its online supplementary material. Further inquiries can be directed to the corresponding author.