A Rare Case of a Solitary Fibrous Tumor in a Child, Presenting as a Congenital Mass, Displaying NAB2ex4::STAT6ex2 Gene Fusion with an Incidental Ganglioneuroblastoma

A solitary fibrous tumor (SFT) is a ubiquitous tumor that occurs across all ages. It is rarely reported in pediatric patients, especially as a congenital mass. A 1 year 7-month old male child presented with a slow-growing gluteal mass since birth along with a recent episode of bleeding. Magnetic resonance imaging (MRI) showed a well-defined, T1-hypointense and T2-hyperintense mass in the skin and the subcutaneous plane. Subsequently, he underwent a surgical resection that revealed a 5.7 cm-sized fleshy mass. On histopathologic examination, there was a fairly well-circumscribed, cellular spindle cell tumor, with cells arranged in intersecting fascicles and hemangiopericytomatous pattern with areas of hemorrhage and fibrinoid necrosis. Cells revealed mild nuclear atypia. Mitotic figures were up to 8/10 hpf. Immunohistochemically, the tumor cells were diffusely positive for CD34 and STAT6. Furthermore, the tumor revealed NAB2 exon 4:: STAT6 exon 2 fusion by RT-PCR and Sanger sequencing. Post-excision, during follow-up, the patient developed an adrenal mass that was histopathologically proven as a neuroblastic tumor, not further specified on biopsy and finally as ganglioneuroblastoma, intermixed type on excision. This constitutes one of the rare cases of SFT in a pediatric patient, presenting as a congenital mass, confirmed by STAT6 immunostaining and further, molecular testing. A review of literature of similar cases, including treatment-related implications, is presented.

Second Report of PDE10A-BRAF Fusion in Pediatric Spindle Cell Sarcoma With Infantile Fibrosarcoma-Like Morphology Suggesting PDE10A-BRAF Fusion Is a Recurrent Event

Infantile/congenital fibrosarcoma (IFS) is the most common soft tissue tumor in children less than one year of age. The most common anatomic site of IFS is in the extremities or trunk, and rarely in the abdomen or retroperitoneum. Approximately 70-90% of cases are characterized by a distinct t(12;15)(p13;q25) translocation resulting in an ETV6-NTRK3 gene fusion. As such, TRK inhibitors are considered frontline therapy in TRK-fusion positive IFS. The ETV6-NTRK3 fusion is also detected in congenital mesoblastic nephroma (CMN) and less frequently in myeloid leukemias, secretory breast carcinoma, and mammary-type secretory carcinoma of the skin and salivary glands. Infrequently, cases of tumors with IFS-like morphology without the characteristic ETV6-NTRK3 gene fusion have been identified. Herein, an ETV6-NTRK3 fusion negative spindle cell sarcoma with IFS-like morphology subjected to genomic profiling revealed a PDE10A-BRAF fusion, a fusion event that has been detected previously in an isolated case of undifferentiated infantile sarcoma.

Non-malignant fibroblastic/myofibroblastic tumors in pediatric age group: Clues and pitfalls to the cytological diagnosis

INTRODUCTION

Fibroblastic/myofibroblastic tumors constitute 12% of all pediatric soft tissue tumors with the majority of them belonging to the benign and intermediate prognostic categories. They are often misdiagnosed owing to their variable clinical presentation and unusual microscopic features. The diagnosis, specially cytological diagnosis of benign and intermediate categories is difficult due to paucity of cellular component and increased amount of extracellular matrix as compared to malignant ones. We hereby discuss the Fine needle aspiration cytology (FNAC) findings of non-malignant fibroblastic/myofibroblastic lesion in the pediatric age group encountered at our institute.

METHODS

All the benign and intermediate fibroblastic/myofibroblastic/fibroadipocytic lesions (age 0-12 years) diagnosed on FNAC over a period of 3½ years (Jan 2016- July 2019), with availability of corresponding histopathology were included in the study.

RESULTS

A total of seven pediatric benign and intermediate fibroblastic/myofibroblastic lesions with histopathological confirmation were identified which included Infantile digital fibromatosis (IDF) (n = 2), Lipofibromatosis (n = 1), Fibrous hamartoma of infancy (FHI) (n = 1), Fibromatosis colli (FC) (n = 2) and myofibroma/myofibromatosis (n = 1). FNAC smears were mainly paucicellular with presence of benign spindle shaped cells in a collagenous stroma common to almost all the cases. A few additional findings such as degenerated skeletal muscle fibres, muscle giant cells and mature adipose tissue were also present in some cases.

CONCLUSION

Fibroblastic/myofibroblastic tumors although uncommon, form an important category that must be considered in the differential diagnosis of pediatric soft tissue tumors. FNAC cytology features when assessed in a proper clinical setting (specially the age and site of presentation) are helpful in suggesting probable preoperative diagnosis in these lesions.

Fibrous hamartoma of infancy

Fibrous hamartoma of infancy (FHI) is a rare, benign tumor of the subcutis and lower dermis, which usually occurs within the first 2 years of life. Ninety one percent of the tumors occur in the first year of life. The histogenesis of FHI is unclear. The clinical course is typically benign and prognosis excellent. The physical characteristics of the subcutaneous mass in a child may suggest a malignant process; however, FHI should be included in the differential diagnosis. The prognosis of FHI is excellent with local surgical excision and it rarely recurs.