Dermal lipofibromatosis-like neural tumor

Dermatomyofibromas harbor PDGFRB mutations - another tyrosine kinase-driven neoplasm

Platelet-derived growth factor receptor beta (PDGFRB) is one of the numerous members of the receptor tyrosine kinase protein family. When altered, it is known to be the driver mutation in different mesenchymal neoplasms, such as pericytic tumors, inflammatory myofibroblastic tumor, and sarcomas with myogenic differentiation. We investigated seven dermatomyofibromas for the presence of a PDGFRB mutation. Patients were 6 females and 1 male. Ages ranged from 2 to 59 years. Neoplasms were located in the shoulder (2), neck (2), upper arm (1), knee (1), and calf (1). Clinically, they appeared as ill-defined plaques. Complete excision was performed in four cases. In three cases, only a biopsy was taken. Histomorphologically, these dermal ill-defined tumors consisted of fascicles of slender myofibroblastic cells oriented often parallel to the epidermis. Their nuclei were monomorphic and elongated, and the cytoplasm was inconspicuous. Involvement of the superficial subcutis was seen in four cases. Immunohistochemically, neoplasms expressed SMA (5/7), focally desmin (1/5), and CD34 (4/6), while S100 was lacking (0/7). By DNA or RNA sequencing, PDGFRB activating mutations were identified in 6/7 tumors. Four neoplasms harbored a mutation in exon 12 encoding for the juxtamembrane domain and 2 neoplasms in exon 14 encoding for the tyrosine kinase domain. Sequencing analyses results highlight that these benign skin tumors belong to the broad spectrum of tyrosine kinase-driven neoplasms.

An Isolated Red Plaque on the Anterior Chest

A 6-year-old girl had a slightly sunken red plaque was observed on the chest, approximately 1.5 cm in diameter, with a smooth surface, associated vascular dilation, well-defined borders, and no scaling or ulceration. What is your diagnosis?

Case Report: Misdiagnosis of a lipofibromatosis-like neural tumor of the dorsal skin as dermatofibrosarcoma protuberans

Background

Lipofibromatosis-like neural tumors (LPF-NT), which have only recently been established, are intermediate soft tissue tumors with neurotrophic tropomyosin receptor kinase 1 (NTRK1) gene alterations and are typically misdiagnosed as dermatofibrosarcoma protuberans, low-grade malignant peripheral nerve sheath tumors, or spindle cell lipoma due to their histopathological and immunohistochemical expression of CD34 and S-100.

Case presentation

The patient was admitted to our hospital with a painless back mass that had appeared more than 4 years prior to admission. Physical examination revealed a subcutaneous mass on the back, approximately 1.5 cm in diameter and protruding into the skin, with clear boundaries and no tenderness. The tumor was surgically resected. The postoperative pathological results suggested a spindle cell soft tissue tumor, and dermatofibrosarcoma protuberan was initially considered. After consultation at a provincial hospital, the patient was diagnosed with a cutaneous lipofibromatosis-like neural tumor of the back. A second extended resection was then performed. Intraoperative rapid freezing examination revealed negative incision margins.

Conclusion

Histological and immunohistochemical detections aid in the differential diagnosis of LPF-NTs. Complete surgical resection is the preferred treatment for LPF-NTs.

Kinase fusion positive intra-osseous spindle cell tumors: A series of eight cases with review of the literature

Mesenchymal spindle cell tumors with kinase fusions, often presenting in superficial or deep soft tissue locations, may rarely occur in bone. Herein, we describe the clinicopathologic and molecular data of eight bone tumors characterized by various kinase fusions from our files and incorporate the findings with the previously reported seven cases, mainly as single case reports. In the current series all but one of the patients were young children or teenagers, with an age range from newborn to 59 years (mean 19 years). Most tumors (n = 5) presented in the head and neck area (skull base, mastoid, maxilla, and mandible), and remaining three in the tibia, pelvic bone, and chest wall. The fusions included NTRK1 (n = 3), RET (n = 2), NTRK3 (n = 2), and BRAF (n = 1). In the combined series (n = 15), most tumors (73%) occurred in children and young adults (<30 years) and showed a predilection for jaw and skull bones (40%), followed by long and small tubular bones (33%). The fusions spanned a large spectrum of kinase genes, including in descending order NTRK3 (n = 6), NTRK1 (n = 4), RET (n = 2), BRAF (n = 2), and RAF1 (n = 1). All fusions confirmed by targeted RNA sequencing were in-frame and retained the kinase domain within the fusion oncoprotein. Similar to the soft tissue counterparts, most NTRK3-positive bone tumors in this series showed high-grade morphology (5/6), whereas the majority of NTRK1 tumors were low-grade (3/4). Notably, all four tumors presenting in the elderly were high-grade spindle cell sarcomas, with adult fibrosarcoma (FS)-like, malignant peripheral nerve sheath tumor (MPNST)-like and MPNST phenotypes. Overall, 10 tumors had high-grade morphology, ranging from infantile and adult-types FS, MPNST-like, and MPNST, whereas five showed benign/low-grade histology (MPNST-like and myxoma-like). Immunohistochemically (IHC), S100 and CD34 positivity was noted in 57% and 50%, respectively, while co-expression of S100 and CD34 in 43% of cases. One-third of tumors (4 high grade and the myxoma-like) were negative for both S100 and CD34. IHC for Pan-TRK was positive in all eight NTRK-fusion positive tumors tested and negative in two tumors with other kinase fusions. Clinical follow-up was too limited to allow general conclusions.

Lipofibromatosis-like neural tumors: Report of a case and review of 73 reported cases

Lipofibromatosis-like neural tumors (LPF-NTs) are a recently discovered group of spindle cell tumors defined by the presence of a lipofibromatosis-like pattern, CD34 and/or S100 reactivity, and frequent neurotrophic receptor tyrosine kinase 1 (NTRK1) gene rearrangements. As new cases emerge, the spectrum of features observed in LPF-NTs continues to evolve. Here we describe the case of an 11-year-old with LPF-NT with a dermatofibrosarcoma protuberans-like honeycomb pattern, CD34 and S100 co-expression, and an NTRK1 rearrangement. We also review the clinical and molecular features of the 73 cases of LPF-NT previously described in the literature.