Fibrous hamartoma of infancy: a clinicopathologic study of 145 cases, including 2 with sarcomatous features

Pearls and Updates on Pediatric Tyrosine Kinase-Altered Tumors

Receptor tyrosine kinases (RTKs) are crucial cell surface receptors that activate intracellular signaling pathways in response to external stimuli, regulating cell proliferation and survival. Under normal conditions, RTK activity is tightly regulated. In pediatric tumors, particularly mesenchymal neoplasms, chromosomal rearrangements are the primary mechanism of RTK-driven oncogenesis, involving genes like NTRK1/2/3, ALK, ROS1, RET, EGFR, and PDGFRB. This review highlights recent advances in understanding RTK-driven myofibroblastic tumors, focusing on the molecular characteristics that influence their classification and clinical behavior. Integration of morphologic, immunophenotypic, and molecular information is essential for accurate diagnosis, given the complex overlap among these tumors.

[Pediatric cutaneous mesenchymal tumors: How to cope with small samples?]

This review article deals with the diagnosis of superficial mesenchymal tumours in children. This is not a comprehensive review, but it focuses on the issue of diagnosis on small samples, especially on fine needle biopsies, which are more and more frequent. A selection of difficult diagnostic situations are discussed, including the case of spindle-cell tumours with variable adipocytic component, some fibrohistiocytic tumours, myofibromas, and vascular tumours. The key messages are the technical requirements in relation to the small sample size, the essential nature of clinical data in paediatric pathology and primarily the age, which is crucial not only for establishing the differential diagnosis but also for choosing the relevant ancillary techniques, and last, the utility of cytogenetics, mainly FISH, and of wisely used molecular biology techniques.

LINC00261 triggers DNA damage via the miR-23a-3p/CELF2 axis to mitigate the malignant characteristics of 131I-resistant papillary thyroid carcinoma cells

Background

Long-chain non-coding RNA (LINC00261) in the treatment of papillary thyroid carcinoma (PTC) with 131I is still unknown despite its proven anti-tumour effect in thyroid cancer (TC) and other types of cancer.

Methods

The database and RT-qPCR were used to analyze the expression level of LINC00261 in PTC and cell lines. PTC cells resistant to 131I (TPC-1/R) were created through ongoing exposure to a lethal dose of 131I, and a subcutaneous xenotransplantation model was developed using PTC mice. Bioinformatics analysis and dual-luciferase assays demonstrated the interaction between LINC00261, miR-23a-3p, and CELF2. RT-qPCR and Western blot were used to detect the expression of LINC00261, miR-23a-3p, and CELF2. Additionally, CCK-8, flow cytometry, immunofluorescence (IF), Western blot, and comet assay were employed to measure cell viability level and DNA damage.

Results

PTC cell lines exhibited a decrease in the expression of LINC00261. The growth and progression through the S-phase of TPC-1/R cells were suppressed by LINC00261, leading to increased apoptosis and DNA damage. The objective of LINC00261 was to regulate the axis of miR-23a-3p/CELF2. Downregulating LINC00261 enhances the growth and advancement of 131I-resistant cells in the S-phase by activating the miR-23a-3p/CELF2 pathway while suppressing cell death and DNA harm. The miR-23a-3p/CELF2 axis activates DNA damage in 131I-resistant PTC cells by LINC00261.

Conclusions

LINC00261 activates DNA damage in 131I-resistant PTC cells caused by miR-23a-3p/CELF2 axis, improving the progression of cancer cells of PTC.

Management of Fibrous Hamartoma of Infancy: A Contemporary Series

BACKGROUND

Fibrous hamartoma of infancy (FHI) is a rare, benign, soft tissue mass that may be locally infiltrative. Primary excision is the mainstay of treatment; however, given the infiltrative nature, margin negativity can be difficult to achieve. The management of residual disease in the setting of positive margins after primary excision is not well described.

METHODS

All patients undergoing FHI excision from 2012 to 2022 were included. Demographics, operative data, margin status, recurrence, and post-operative follow-up data were obtained via retrospective chart review.

RESULTS

Nine patients were identified who underwent FHI excision. The median age at time of excision was 9 months (IQR 16). Seven (78%) were male, and the majority (78%) were white. Seven (78%) underwent preoperative imaging via ultrasound or MRI, and 4 (44%) had a preoperative biopsy to confirm diagnosis. Common locations included upper extremity (n = 4, 44%) and lower extremity/inguinal region (n = 4, 44%). Six patients (67%) had positive margins on pathology - 3 (33%) on the upper extremity, 2 (22%) on the lower extremity/inguinal region, and one (11%) on the flank. One patient (11%) had a local recurrence which did not undergo re-excision.

CONCLUSIONS

FHI remains a rare diagnosis. There is a high margin positivity rate; however, local clinically significant mass recurrence remains uncommon. With low rates of clinically significant mass development coupled with the benign nature of disease, a "watch and wait" approach may be appropriate for patients with positive histologic margins after complete gross excision to avoid reoperation and need for complex reconstructions.

LEVEL OF EVIDENCE

Level 4.

Spindle Cell Lesions with Oncogenic EGFR Kinase Domain Aberrations: Expanding the Spectrum of Protein Kinase-Related Mesenchymal Tumors

EGFR aberrations are reported in a subset of myofibroblastic lesions with kinase domain duplication (EGFR-KDD) and exon 20 mutations being assigned to infantile fibrosarcomas (IFS), mesoblastic nephroma, and fibrous hamartoma of infancy (FHI), respectively. In this retrospective study, we correlated molecular findings with the histomorphology of 14 myofibroblastic lesions harboring such genetic changes identified by NGS. We additionally performed DNA methylation profiling (DNAmp) and immunohistochemistry. Lesions were from 10 males and 4 females with a mean age of 3 years (range, 0.3-14) and occurred subcutaneously in the upper limbs (n = 5), lower limbs (n = 3), back/thorax (n = 5), and the nasal cavity (n = 1). Eleven were cured by surgery, including 1 relapsed case. Two patients were lost to follow-up. One case was very recent, and the patient was biopsied. Histologically, the lesions showed a wide spectrum varying from classic FHI (n = 9) to IFS (n = 1) or lipofibromatosis-like tumors (LFT-like) (n = 2) or dermatofibrosarcoma protuberans-like (DFSP-like) (n = 1) to a predominantly myxoid spindle cell lesion (n = 1). Immunohistochemically, all neoplasms stained with CD34, whereas S100 was positive in 2/14. EGFR expression was observed in 9/10 cases. Molecularly, the IFS and 1 LFT-like harbored EGFR-KDD, whereas an exon 20 mutation was identified in all FHI, 1 LFT-like, the DFSP-like, and in predominant myxoid spindle cell lesion. By DNAmp, all but 2 cases formed a well-defined cluster, demonstrating that these lesions are also epigenetically related. In conclusion, EGFR kinase domain aberrations found in FHI, IFS, LFT-like, DFSP-like, and a spindle cell lesion with a predominant myxoid stroma of children and adolescents showed that these neoplasms with a broad morphologic spectrum belong to the group of protein kinase-related lesions with a distinct epigenetic signature. Molecular analyses, including DNAmp, help to identify and characterize this emerging category and become mandatory when targeted treatment is considered.

Dermatologic Review in Pediatric Vascular Lesions

Vascular anomalies (VAs) can be present in any organ; however, the skin being the largest one, it is there where many of them are evident; some are visible at birth, others develop throughout life. Pediatric dermatologists are specially trained to distinguish VAs from their mimickers, which require different treatments and may harbor distinct prognoses. We resume the diagnostic and therapeutic tasks of pediatric dermatologist at our vascular anomaly clinics, as well as the differential diagnoses of mimickers of VAs.

Fibrous hamartoma of infancy of the spinal cord resembling conus and filum, with a coexisting sacral dimple

Fibrous hamartoma of infancy (FHI) is a rare benign soft tissue lesion of infants and young children. It usually occurs within the first 2 years of life at the superficial layer of the axilla, trunk, upper arm, and external genitalia. FHI in the central nervous system (CNS) is extremely rare. So far, only two spinal cord FHI cases have been reported. We present a case of a 1-month-old girl who presented with a skin dimple in the coccygeal area. Her MRI showed a substantial intramedullary mass in the thoracolumbar area with a sacral soft tissue mass and a track between the skin lesion to the coccygeal tip. Her normal neurological status halted immediate surgical resection. A skin lesion biopsy was first performed, revealing limited information with no malignant cells. A short-term follow-up was performed until the intramedullary mass had enlarged on the 5-month follow-up MRI. Based on the frozen biopsy result of benign to low-grade spindle cell mesenchymal tumor, subtotal resection of the mass was done, minimizing damage to the functioning neural tissue. Both the skin lesion and the intramedullary mass were diagnosed as FHI. Postoperative 5.5-year follow-up MRI revealed minimal size change of the residual mass. Despite being diagnosed with a neurogenic bladder, the patient maintained her ability to void spontaneously, managed infrequent UTIs, and continued toilet training, all while demonstrating good mobility and no motor weakness. This case is unique because the lesion resembled the secondary neurulation structures, such as the conus and the filum, along with a related congenital anomaly of the dimple.

Lipoblastoma Arising in the Head and Neck: A Clinicopathologic Analysis of 20 Cases

BACKGROUND

Lipoblastomas (LPBs) are benign adipocytic neoplasms believed to recapitulate the development of embryonal fat.

METHODS

We investigated the clinicopathologic and immunohistochemical features of 20 lipoblastomas arising in the head and neck in 18 patients.

RESULTS

Patients included 6 males and 12 females (1:2 ratio) with age at diagnosis ranging from 4 months to 28 years. Tumors occurred more commonly in the neck (12, 66.7%) and less commonly in the forehead, scalp, and tongue (2, 11.1%). Tumor size ranged from 1.4 to 6.0 cm (median 5.0 cm). Two patients, a 4-month-old female and 3-year-old male, had local recurrence of neck tumors at 4 months and 3 years after excision, respectively. Microscopically, tumors had a lobulated growth pattern and consisted of adipocytes at varying stages of differentiation. In addition to the classical histologic features, lipoma-like and myxoid variants constituted 45% of cases. Metaplastic elements, including brown fat and cartilage, were identified in two cases.

CONCLUSIONS

LPBs arising in the head and neck region are not uncommon and occurred at a rate of 9% in our cohort. They should be kept in the differential diagnosis when a fatty tumor is encountered in an older child or occurring at an unusual location.

Fibrous hamartoma of infancy: imaging findings

BACKGROUND

Fibrous hamartoma of infancy is a benign tumor that typically arises within the first 2 years of life in the subcutaneous and lower dermal layers. Diagnosis can be challenging as it is a rare tumor, and the imaging appearance is not well known.

OBJECTIVE

To describe the imaging features in 4 cases of fibrous hamartoma of infancy focusing on ultrasound (US) and magnetic resonance (MR) findings.

MATERIALS AND METHODS

In this retrospective IRB-approved study, informed consent was waived. We searched patient charts for histopathology-confirmed fibrous hamartoma of infancy diagnosis between November 2013 and November 2022. We found four cases, three boys and one girl, and the mean age was 1.4 years (5 months-3 years). The lesions were located in the axilla, posterior elbow, posterior neck, and lower back. All four patients underwent ultrasound evaluation of the lesion, and two patients also underwent MRI evaluation. The imaging findings were reviewed by consensus by two pediatric radiologists.

RESULTS

US imaging revealed subcutaneous lesions with variably defined hyperechoic regions and intervening hypoechoic bands resulting in a linear "serpentine" pattern or a "multiple semicircle" pattern. MR imaging evidenced heterogeneous soft tissue masses, localized in the subcutaneous fat, and showed hyperintense fat interspersed with hypointense septations on both T1- and T2-weighted images.

CONCLUSION

Fibrous hamartoma of infancy has a suggestive appearance on US with heterogeneous, echogenic subcutaneous lesions with intervening hypoechoic portions, in parallel or circumferential arrangement that can be seen as a serpentine or semicircular pattern. On MRI, interspersed macroscopic fatty components show high signal intensity on T1- and T2-weighted images and reduced signal on fat-suppressed inversion recovery images, with irregular peripheral enhancement.

Fat-Containing Soft Tissue Tumors in Children, Adolescents, and Young Adults: Which Require Biopsy?

PURPOSE

To confirm the overall benignity of fat-containing soft tissue tumors (STT) on a pediatric cohort and to define the clinical and imaging features that warrant a biopsy.

METHODS

A retrospective monocentric study was conducted on patients aged less than 25 years consecutively referred for fat-containing STT to our Comprehensive Cancer Center between 1998 and 2022. Tumor imaging characteristics at diagnosis (US, CT, or MRI) were correlated with pathology.

RESULTS

The database extraction identified 63 fat-containing tumors with clinical, histologic, and imaging data available for review. In total, 58 (92%) were benign tumors: 36 lipoblastomas and lipomas, 12 fibrous hamartomas of infancy (FHI), 5 lipofibromatosis, 2 lipomas arborescens, 2 lipomatosis and 1 spindle-cell lipoma. Five patients (8%) were diagnosed with liposarcoma. Factors significantly correlated with malignancy were age >10 years old (p < 0.001), having a cancer-predisposing condition (p < 0.001), a percentage of fat <25% (p = 0.002), and a presence of myxoid zones (p < 0.001) on imaging.

CONCLUSION

Most fat-containing STT in children may be classified as benign tumors based on clinics and imaging. The indication for biopsy could be limited to patients aged 10 years or more with either a cancer-predisposing condition or imaging features demonstrating either a low-fat component (<25%) or the presence of myxoid zones.

TFG::MET-rearranged soft tissue tumor: A rare infantile neoplasm with a distinct low-grade triphasic morphology

This article presents 2 cases of TFG::MET-rearranged mesenchymal tumor, an extremely rare molecular subset among an emerging group of mesenchymal neoplasms with kinase gene (NTRK, BRAF, RET and others) alterations. Both tumors were congenital, occurred in female patients and presented as huge masses on the trunk and thigh, measuring 18 and 20 cm in the largest dimension. Both cases showed identical areas with a distinctive triphasic morphology resembling fibrous hamartoma of infancy (FHI), consisting of haphazardly arranged ovoid to spindled cells traversed by variably cellular and hyalinized fascicles admixed with (most likely non-neoplastic) adipose tissue. In other areas, a high-grade infantile fibrosarcoma/malignant peripheral nerve sheath tumor-like (IFS/MPNST-like) morphology was present in both cases. While the first case co-expressed CD34 and S100 protein, the other case did not. When combined with the three previously reported MET-rearranged cases (of which two harbored TFG::MET fusion), 3/5 and 3/4 of MET-rearranged and TFG::MET fusion-associated tumors, respectively exhibited similar triphasic FHI-like low-grade morphology. This points toward the existence of a relatively distinct morphological subset among kinase-fusion-associated tumors which seems to be strongly associated with MET fusions. It seems some of these low-grade cases may transform into a high-grade variant with IFS/MPNST-like morphology as has been observed in other tumors with kinase gene fusions. While most cases seem to follow an indolent clinical course, the recognition of these tumors is clinically relevant as MET tyrosine kinase inhibitors might represent an effective treatment option for clinically aggressive or unresectable cases.

Subcutaneous fat necrosis of the newborn: a pictorial essay of an under-recognized entity

Subcutaneous fat necrosis of the newborn is a self-limited disorder predominantly affecting full-term and post-term neonates during the first 6 weeks after birth. Subcutaneous fat necrosis can be focal or multifocal and affect one or both sides with a predilection for areas of pressure in certain anatomical areas. Subcutaneous fat necrosis of the newborn is associated with perinatal asphyxia and other neonatal and maternal risk factors. Subcutaneous fat necrosis of the newborn presents as a self-limited area of dermal edema followed by indurated subcutaneous plaques, or nontender and mobile nodules, sometimes with skin discoloration [1-3]. The diagnosis is based on the child's history and physical examination, but when in doubt, imaging is helpful. US is the imaging modality of choice to confirm the diagnosis of subcutaneous fat necrosis of the newborn because it provides the best resolution of superficial lesions, requires no sedation and lacks ionizing radiation. US can also help evaluate and characterize other pathologies affecting the superficial subcutaneous soft tissues at this age. Familiarity with subcutaneous fat necrosis of the newborn is important to make a prompt and precise diagnosis and avoid unnecessary imaging tests or invasive procedures.

Fibrous hamartoma of infancy. Radiologic-pathologic study of 21 cases: 8 with predominant pseudoangiomatous pattern

Fibrous hamartoma of infancy (FHI) is a very rare benign soft tissue lesion that principally affects the axilla, trunk, and upper extremities of children younger than 2 years. It is usually cured by local excision. Histologically, these lesions have a triphasic morphology in an organoid pattern: mature adipose tissue, fibroblastic/myofibroblastic trabeculae, and small round cell nests in a myxoid matrix. However, morphologic variants have recently been described. Focal areas with a pseudoangiomatous pattern have been found in some FHI, but few cases with predominant pseudoangiomatous areas have been previously described in the medical literature. We report 21 new cases of FHI, 8 of them with a predominant pseudoangiomatous pattern. Our cases with a predominant pseudoangiomatous pattern did not present specific radiological findings.

Infantile Fibrosarcoma and Other Spindle Cell Neoplasms of Infancy. A Review of Morphologically Overlapping yet Molecularly Distinctive Entities

BACKGROUND

Regardless of age at presentation, many soft tissue neoplasms have overlapping histopathologic and immunophenotypic features to serve as a diagnostic challenge.

CASE REPORT

We reported a case of a spindle cell neoplasm in an infant, which was initially considered a vascular anomaly clinically and an eventual biopsy revealed marked inflammation with a spindle cell component that was resolved as an infantile fibrosarcoma with an ETV6 break-apart.

CONCLUSION

The context of this case lead to a further consideration of various other spindle cell neoplasms arising predominantly in the soft tissues during the infancy period as defined by the first two years of age. Though sharing similar morphologic features, these tumors can be categorized into several molecular genetic groups, which have provided both diagnostic and pathogenetic insights as well as treatment options in some cases.

Lipoblastoma in one adult and 35 pediatric patients: Retrospective analysis of 36 cases

Lipoblastoma is a rare benign mesenchymal neoplasm that typically occurs at various sites in infants and children but may also occur in adults. Thus, differential diagnoses are often performed. To understand this tumor type, the present study described clinicopathological features, diagnosis and differential diagnosis of different morphological lipoblastomas. A single-institution retrospective review of 36 lipoblastoma cases diagnosed between 2015 and 2021 was performed. Formalin-fixed paraffin-embedded tissue was used for S-100, CD34, P16 and desmin immunohistochemistry analysis, along with rapid fluorescence in situ hybridization (FISH) detection with pleiomorphic adenoma gene 1 (PLAG1). The 36 cases included 14 females and 22 males [age range, 7 days to 33 years (median, 16.5 years); 28 patients were aged ≤3 years] and the tumors were located in the trunk (n=16), limbs (n=12), head and neck (n=6), and perineum (n=2). Histologically, lipoblastomas were divided into classic (n=15), lipoma-like (n=13) and myxoid (n=8) subtypes. They comprised lobules of mature adipose tissue of varying size and a fine capillary network surrounded by mucinous stroma. Single- or multivesicular lipoblasts positive for S-100 (29/36, 81%) were observed, with occasional mature adipocytes. Peripheral vessels and cytoplasm of primitive mesenchymal cells were diffusely positive for CD34 (36/36, 100%), whereas primitive mesenchymal cells and striated muscle tissue were positive for desmin (26/36, 72%). Most tumor cells were negative while only few were positive for P16 (8/36, 22%). FISH revealed PLAG1 breakage and rearrangement in 24/32 (75%) patients. In total, 28 patients were followed up post-operatively (range, 2-84 months; median, 41 months; 3 patients relapsed and 8 were lost to follow-up). In conclusion, diagnosis of a typical lipoblastoma is not difficult and PLAG1 breakage detection is key for the diagnosis.

Fibrous hamartoma of infancy with bone destruction of the tibia: A case report

BACKGROUND

Fibrous hamartoma of infancy (FHI) is a rare disease of infancy with unknown etiology. The disease mainly involves soft tissue, has no specific clinical manifestations, and is difficult to diagnose. At present, the diagnosis is mainly confirmed by histopathological examination, and the main treatment is surgical resection of the pathological tissue, which is prone to recurrence.

CASE SUMMARY

A five-month-old female patient was admitted to our hospital with swelling in the right calf. Two biopsies were performed in our hospital and another hospital, respectively, confirming the diagnosis as fibrous hamartoma. After exclusion of surgical contraindications, resection was performed with clear margins of 1 cm. Radiographic examination showed tumor recurrence more than four months after the operation, and surgery was performed again to extend the resection margins to 1.5 cm. The patient is recovering well, and after a follow-up of 36 mo, shows no signs of recurrence.

CONCLUSION

Our case report demonstrates that FHI should be considered in the differential diagnosis for a lower extremity mass with bone destruction. For FHI with bone destruction and unclear boundaries, excision margins of 1.5 cm could be superior to margins of 1 cm.

Scrotal fibrous hamartoma of infancy: A case report and literature review of a rare tumor of the genitourinary tract

Fibrous hamartoma of infancy (FHI) is a rare, benign soft tissue lesion observed in infants characterized histologically by triphasic appearance of bland fibroblastic fascicles, mature adipose tissue, and nodules of primitive myxoid mesenchyme. Preoperative and intraoperative recognition of FHI presents a significant diagnostic challenge due to nonspecific imaging findings and its histologic similarities to alternate benign and malignant entities. Management requires complete local excision and clinical follow-up to monitor for recurrence. Here, we present the diagnosis, management, and two-year follow-up of a 13-month-old boy with a scrotal FHI in addition to a comprehensive literature review of this entity.

Giant dorsal lipofibromatosis in an infant: a case report

BACKGROUND

Lipofibromatosis is a rare, benign, soft tissue tumor that usually presents in children. Low incidence and lack of specificity in clinical presentation make its diagnosis difficult.

CASE PRESENTATION

This is a case report of a patient with a giant lipofibromatosis on the back that resembles an infantile hemangioma, which posed great difficulty in diagnosis due to atypical clinical manifestations. After the postoperative pathological and immunohistochemical examination and fluorescence in situ hybridization, the patient was finally diagnosed with lipofibromatosis.

CONCLUSIONS

The incidence of fibromatosis was low. This case presents an atypical clinical manifestation since the tumor growth was on the back, and this can easily cause misdiagnosis. This case suggests that the diagnosis of lipofibromatosis depends on the pathology and fluorescence in situ hybridization.

CT and MRI Features of Middle Ear Fibrous Hamartoma of Infancy: A Case Report

Fibrous hamartoma of infancy in the middle ear is extremely rare. We report the case of a 26-month-old male patient who presented with a mass in the left middle ear. A temporal bone CT scan showed complete opacification of the left middle ear and mastoid air cells without ossicular erosion. On MRI, the mass revealed heterogeneous signal intensities indicative of fat and fibrous components. A definitive diagnosis was made postoperatively based on the histological results. Although rare, fibrous hamartoma of infancy should be considered as a differential diagnosis of a middle ear mass during childhood.

Pediatric and Infantile Fibroblastic/Myofibroblastic Tumors in the Molecular Era

Pediatric fibroblastic/myofibroblastic tumors are rare but include a wide variety of benign to malignant tumors. Given their uncommon frequency, they may present as a diagnostic dilemma. This article is focused on using clinical and pathologic clues in conjunction with the increasingly relevant and available molecular techniques to classify, predict prognosis, and/or guide treatment in these tumors.

Update on Superficial Spindle Cell Mesenchymal Tumors in Children

The diagnosis of cutaneous and subcutaneous spindle cell neoplasms in children is often challenging and has potential therapeutic and prognostic implications. Although correctly diagnosing dermatofibrosarcoma protuberans and infantile fibrosarcoma is paramount, pathologists should not ignore a number of diagnostic pitfalls linked to mostly rare tumors with completely different clinical outcomes. In the last decade, a spectrum of novel entities has been described; information from molecular biology has helped to shape this new landscape for spindle cell tumors. Here, we review the most noteworthy neoplasms in this spectrum, with a focus on their histological similarities: fibroblastic connective tissue nevus, medallion-like dermal dendrocyte hamartoma, or plaque-like CD34-positive dermal fibroma, which share features with fibrous hamartoma of infancy; lipofibromatosis and lipofibromatosis-like neural tumor; and plexiform myofibroblastoma, a recently described neoplasm that should be distinguished from plexiform fibrohistiocytic tumor. These tumors also have genetic similarities, particularly gene rearrangements involving NTRK3 or NTRK1. These genetic features are not only essential for the differential diagnosis of infantile fibrosarcoma but are also of diagnostic value for lipofibromatosis-like neural tumors. The more recently described RET, RAF1, and BRAF gene fusions are also discussed.

Fibrous Hamartoma of Infancy: A Series of 21 Cases and Review of the Literature

BACKGROUND

Fibrous hamartoma of infancy (FHI) is a rare soft-tissue tumor usually seen in infants and young children. Histologically, the tumor is characterized by a triphasic morphology, and the clinical course is benign.

METHODS

We described the histopathologic and immunohistochemical features in a series of 21 cases of FHI and reviewed the main entities to consider in differential diagnosis.

RESULTS

Most patients in the series were male. The mean age was 3.7 years (range, 5 months-24 years), and lesions were found in locations that have been previously reported. Histopathologically, the tumors were composed of variable proportions of fibroblastic, mesenchymal, and mature adipose tissue. Three of the 13 immunohistochemically stained biopsies (14%) contained hyalinized zones with cracking artifacts, mimicking giant cell fibroblastoma. Eight of the 13 stained with smooth-muscle actin (61%) were positive in the fibroblastic component, 6 of the 8 stained with CD34 (75%) were positive in the immature mesenchymal and fibroblastic components, and all 7 stained with S100 were positive (100%) in adipose tissue.

CONCLUSIONS

Our histopathologic findings are consistent with those described in larger series. However, in order to reach a precise diagnosis and plan treatment, clinical heterogeneity obliges us to become familiar with variations in the characteristic triphasic histology of FHI.

The RNA-Binding Protein CELF2 Inhibits Ovarian Cancer Progression by Stabilizing FAM198B

An increasing number of studies have clarified the functional roles of RNA-binding proteins (RBPs) in driving post-transcriptional mechanisms of cancer progression. In this study, we integrated data from the RBP database and Gene Expression Omnibus (GEO) data with RNA sequencing (RNA-seq) data from 10 ovarian cancer tissues and 8 normal ovarian tissues and identified an RBP, CUGBP- and ETR-3-like family 2 (CELF2). We found that CELF2 expression was downregulated in ovarian cancer and positively correlated with the overall survival (OS) and progression-free survival (PFS) of patients with ovarian cancer. Altered CELF2 expression led to changes in the proliferation, migration, and invasion of ovarian cancer cells in vitro and in vivo. CELF2 expression increased the stability of its target, FAM198B, by binding to AU/U-rich elements (AREs) in the 3' untranslated region (3' UTR). FAM198B knockdown restored the CELF2-mediated suppression of proliferation and migration. We also found that CELF2/FAM198B may repress ovarian cancer progression by inhibiting the mitogen-activated protein kinase/extracellular-regulated protein kinase (MAPK/ERK) signaling pathway. Finally, a curcumin-induced increase in CELF2 expression resulted in increased ovarian cancer cell sensitivity to cisplatin. Our study elucidated a novel mechanism by which the CELF2/FAM198B axis regulates proliferation and metastasis in ovarian cancer, providing novel, potential therapeutic targets for ovarian cancer.

Advances in the Diagnosis and Management of Neonatal Sarcomas

Neonatal sarcomas comprise a heterogeneous group of rare soft tissue neoplasms that present unique diagnostic and therapeutic challenges. Recent advances in molecular profiling have improved diagnostic capabilities and reveal novel therapeutic targets. Clinical trials demonstrate differences in behavior between sarcoma subtypes that allow for better clinical management. Surgical resection has been replaced with a multimodal approach that includes chemotherapy and radiotherapy. Despite these advances, neonates with sarcoma continue to fare worse than histologically similar sarcomas in older children, likely reflecting differences in tumor biology and the complexities of neonatal medicine. This review focuses on recent advances in managing neonatal sarcomas.

Soft Tissue Special Issue: Fibroblastic and Myofibroblastic Neoplasms of the Head and Neck

Fibroblastic and myofibroblastic neoplasms of the head and neck encompass a group of rare tumor types with often overlapping clinicopathologic features that range in biologic potential from benign to overtly malignant. Even neoplasms with no metastatic potential may provide significant therapeutic challenges in this region due to the unique anatomy of the head and neck. This review will cover the following entities, highlighting important clinical aspects of each neoplasm and then focusing on their characteristic histomorphology, immunophenotype, and molecular alterations: nodular and cranial fasciitis, fibrous hamartoma of infancy, nasopharyngeal angiofibroma, nuchal-type and Gardner fibromas, desmoid fibromatosis, dermatofibrosarcoma protuberans and giant cell fibroblastoma, solitary fibrous tumor, inflammatory myofibroblastic tumor, low-grade myofibroblastic sarcoma, infantile fibrosarcoma, low-grade fibromyxoid sarcoma, and sclerosing epithelioid fibrosarcoma. While some of these neoplasms characteristically arise in the head and neck, others are rarely described in this anatomic region and may therefore be particularly difficult to recognize. Distinction between these entities, however, is crucial, particularly as the molecular pathogenetic basis for these neoplasms are being rapidly elucidated, in some instances allowing for targeted therapeutic approaches.

A rare cause of unilateral breast swelling in a male infant caused by fibrous hamartoma of infancy combined with pseudoangiomatous stromal hyperplasia

We report a case of a male infant who underwent resection of a unilateral breast mass with a histopathological diagnosis of a fibrous hamartoma of infancy (FHI) combined with a pseudoangiomatous stromal hyperplasia (PASH). Breast lumps are uncommon in infants and children, especially in boys. FHI and PASH are very rare causes of breast lumps, especially in infants. To our knowledge, this is the first report of a combination of both pathologies in 1 lesion in the breast of an infant.

Fibrous hamartoma of infancy associated with bony remodeling and muscle atrophy

Fibrous hamartoma of infancy (FHI) is a benign, poorly demarcated, unencapsulated hamartoma contiguous with surrounding fat. This case highlights pronounced bony remodeling and muscle atrophy associated with FHI in a 6-week-old girl. Emphasis is placed on pathologic diagnosis and mechanisms, treatment considerations, and the multidisciplinary approach utilized in the management of the disorder.

Fibrous hamartoma of infancy: radiologic features and literature review

Background

Fibrous hamartoma of infancy(FHI) is a rare benign lesion most frequently occurring within the first year of life. So far, just over 200 cases have been reported in the English literature, in which the radiologic findings of FHI have not been fully described. Herein, 2 adult cases of FHI receiving treatment in our hospital and the published cases searched on PubMed are reviewed, with the emphasis on the discussion of the spectrum of MR findings and their histologic correlation.

Case presentation

We present two adult cases who aged 47 years and 19 years with slow growing masses beginning from their childhood in the posterior craniocervical area. On CT and MR imaging, the tumours showed as the superficially located lesions with ill-defined margins that involved the subcutaneous layer and its underlying muscles. The size of the lesions were 21.3 × 16.7 × 16 cm in case 1 and 20.2 × 19.3 × 13.6 cm in case 2. The tumours demonstrated heterogeneous intensities/signals with the adipose tissue presenting as the disperse strands or small focus of fatty intensity/signal. Parallel or whirling appearance, and dilated vessels were delineated in the cases. Contrast enhancement was administered in case 1 and marked enhancement was found.

Conclusions

The usually observed manifestation of FHI on CT and/or MR imaging is the strands of adipose/fibrous intensities traversing the lesions, with the characteristic parallel or whirling appearance in some cases. The tumours with ill-defined margins have the tendency to involve the underlying muscles. Some fibroblastic and adipocytic tumours should be ruled out in differential diagnosis.

[Pediatric tumors with spindle cell morphology]

Spindle cell tumors in childhood are rare lesions with a heterogeneous morphological picture and clinical course, ranging from benign lesions to fully malignant tumors. The clinical assessment of these tumors is often challenging since some of them show fast growth dynamics but are utterly benign, while a subset of slow-growing tumors can represent malignant entities. Due to the rarity of these tumors as well as the overlapping morphology and the often uncharacteristic immunohistochemical profiles, the pathologic diagnosis is often also difficult. This review gives an overview of some of the more common pediatric spindle cell tumors. In addition to the morphological features and immunohistochemical aspects, specific molecular changes are discussed. Here, some of the newly described translocations that may imply therapeutic options, are presented.

Aberrant receptor tyrosine kinase signaling in lipofibromatosis: a clinicopathological and molecular genetic study of 20 cases

Lipofibromatosis is a rare pediatric soft tissue tumor with predilection for the hands and feet. Previously considered to represent "infantile fibromatosis", lipofibromatosis has distinctive morphological features, with mature adipose tissue, short fascicles of bland fibroblastic cells, and lipoblast-like cells. Very little is known about the genetic underpinnings of lipofibromatosis. Prompted by our finding of the FN1-EGF gene fusion, previously shown to be a characteristic feature of calcifying aponeurotic fibroma (CAF), in a morphologically typical case of lipofibromatosis that recurred showing features of CAF, we studied a cohort of 20 cases of lipofibromatosis for this and other genetic events. The cohort was composed of 14 males and 6 females (median age 3 years; range 1 month-14 years). All primary tumors showed classical lipofibromatosis morphology. Follow-up disclosed three local recurrences, two of which contained calcifying aponeurotic fibroma-like nodular calcifications in addition to areas of classic lipofibromatosis, and no metastases. By FISH and RNA sequencing, four cases were positive for FN1-EGF and one case each showed an EGR1-GRIA1, TPR-ROS1, SPARC-PDGFRB, FN1-TGFA, EGFR-BRAF, VCL-RET, or HBEGF-RBM27 fusion. FN1-EGF was the only recurrent fusion, suggesting that some cases of "lipofibromatosis" may represent calcifying aponeurotic fibroma lacking hallmark calcifications. Several of the genes involved in fusions (BRAF, EGFR, PDGFRB, RET, and ROS1) encode receptor tyrosine kinases (RTK), or ligands to the RTK EGFR (EGF, HBEGF, TGFA), suggesting a shared deregulation of the PI3K-AKT-mTOR pathway in a large subset of lipofibromatosis cases.

Adipocytic tumors in Children: A contemporary review

Adipocytic neoplasms in the pediatric population demonstrate a different histologic spectrum and frequency than in adults. The vast majority of these tumors are benign, with lipoma being the most common entity. The identification of signature cytogenetic and molecular alterations for certain lesions, such as PLAG1 gene rearrangement in lipoblastoma and FUS-DDIT3 fusion in myxoid liposarcoma, has been helpful in approaching these neoplasms and aiding in confirming the diagnosis. Furthermore, it is important for pathologists to recognize that adipocytic neoplasms may be associated with different syndromes with potential impact in managing such patients. This review provides a summary of the clinical pictures, histologic characteristics, molecular alterations, differential diagnoses, and syndromic associations of the commonly encountered fatty tumors in children.

A Rare Case of Fibrous Hamartoma of Infancy: A Clinicopathological Diagnosis at a Tertiary Hospital, Eastern Nepal

Background

Fibrous hamartoma of infancy is a rare soft tissue lesion of infants and young children with characteristic triphasic morphology.

Case Description

An 18-month-old female child was presented with complaints of swelling over right leg shin since birth. On examination, a lump of size 7x3 cm was identified which was mobile and nontender. Local excision was performed and tissue sent for histopathological examination. On gross examination, a globular, capsulated, firm to hard tissue had cut section revealing solid grey-white to grey-brown lesion with myxoid areas identified. Microscopic examination revealed a poorly circumscribed lesion comprising intersecting trabeculae of fibrous tissue, areas of immature oval and stellate cell within myxoid matrix, and varying amounts of interspersed mature fat cells.

Conclusion

Even though fibrous hamartoma of infancy is a rare benign entity with limited clinical knowledge, proper diagnosis is mandatory as its prognosis is excellent.

Fibroblastic and myofibroblastic tumors of children: new genetic entities and new ancillary testing

Fibroblastic and myofibroblastic tumors comprise a morphologically diverse and biologically variable group of neoplasms that affect a wide age range. Specific entities tend to occur most frequently in infants and young children. Recent years have witnessed a proliferation of information concerning the unique biology of these tumors. In this report, I will review recent findings that serve to further characterize this group of neoplasms. Included will be newer information on fibrous hamartoma of infancy, infantile myofibromatosis, lipofibromatosis, and infantile fibrosarcoma and tumors resembling it, including primitive myxoid mesenchymal tumor of infancy and new genetic entities. I will also discuss the differential diagnosis, which includes spindle cell rhabdomyosarcoma, dermatofibrosarcoma protuberans, and calcifying aponeurotic fibroma.

Hamartomas of skin and soft tissue

Hamartomas are benign lesions composed of aberrant disorganized growth of mature tissues. Choristomas are similar, except that they are composed of tissues not normally found at the anatomic site in which the lesion is arising. A wide range of hamartomas and choristomas can arise in the skin and soft tissue. Some of these may cause diagnostic difficulty and potentially be mistaken for neoplasms. Some neoplasms may resemble hamaratomas. Here we review the current clinical and pathologic features of these lesions, both common and rare, and discuss how to distinguish them from other entities in the differential diagnosis.

New advances in the molecular classification of pediatric mesenchymal tumors

Pediatric soft tissue tumors are relatively rare and show significant overlap in morphology and immunoprofile, often posing diagnostic and management challenges. Thus, their classification remains often subjective or lumped under "unclassified categories," as a number of lesions lack objective and reproducible criteria in diagnosis. Although in a subset of cases immunohistochemistry has been proved useful to identify a specific line of differentiation, most tumors lack a readily defined histogenesis, being characterized by a rather non-specific immunoprofile. Furthermore, tumors with an ambiguous diagnosis are difficult to grade and their risk of malignancy or clinical management remains uncertain. Advances in molecular genetics, including the more wide application of next generation sequencing in routine clinical practice, have improved diagnosis and refined classification based on objective molecular markers. Importantly, some soft tissue tumors in children are characterized by recurrent gene fusions involving either growth factors (eg, PDGFB) or protein kinases (eg, ALK, ROS, NTRK, BRAF), which have paved the way for new targeted treatments that block the respective upregulated downstream pathways. However, the majority of gene fusions or mutations detected in soft tissue tumors result in an abnormal function of transcription factors or chromatin remodeling. The present review focuses on the latest genetic discoveries in the spectrum of both benign and malignant pediatric soft tissue neoplasia. These genetic abnormalities promise to provide relevant insight for their proper classification, prognosis, and treatment. The entities discussed herein are grouped either based on their shared genetic mechanism or based on their presumed line of differentiation.

Congenital fibroblastic connective tissue nevi: Unusual and misleading presentations in three infantile cases

BACKGROUND

Fibroblastic connective tissue nevi (FCTN) are benign skin conditions characterized by bland spindle cells infiltrating the reticular dermis and the upper subcutis with preservation of adnexal structures. A subset of FCTN expresses CD34, which may cause difficulties in the differential diagnosis, in particular with dermatofibrosarcoma (DFSP). We aim to study clinical and histological main features of congenital FCTN to better understand their heterogeneity.

METHODS

We present 3 cases of congenital FCTN with misleading pseudo-tumoral presentations and compare them with published cases in literature. We provide a diagnostic algorithm for congenital neonatal connective tissue tumors.

RESULTS

Clinically, FCTN mostly present as well-limited and nontender plaques or nodules mainly located in the neck and face areas or in the trunk. Histologically, FCTN are composed of irregularly distributed fascicles of bland spindled cells and are defined by a list of fundamental features: (i) no atypia, pleomorphism, or mitotic activity; (ii) skin appendages entrapped but unaffected; (iii) no evidence for malignancy. In most cases CD34 is positive, but in some cases, cells can express SMA or are even CD34- and SMA-.

CONCLUSION

The initial presentation and natural history of FCTN fit better with a neoplasm than with a hamartoma. Thus, we suggest replacing the term "nevus" with tumor and considering fibroblastic connective tissue tumor (FCTT) as the right denomination of this clinico-pathological entity. FCTTs are difficult to diagnose due to their clinical heterogeneity. Clinical and histological malignant and benign differential diagnoses are discussed.

Nonepithelial Tumors and Tumor-like Lesions of the Skin and Subcutis in Children

This overview of mesenchymal tumors presenting in the skin and/or subcutis in children brings together the range of neoplasms and hamartomas which are seen in this age-group. It is not surprising from the perspective of the pediatric or general surgical pathologist that vascular anomalies, including true neoplasms and vascular malformations, are the common phenotypic category. Since there is considerable morphologic overlap among these lesions, clinicopathologic correlation may be more important than for many of the other mesenchymal tumors. The skin and subcutis are the most common sites of clinical presentation for the infantile myofibroma which is the most common of fibrous mesenchymal tumors in children. Several of the other mesenchymal tumors are more common adults-like dermatofibrosarcoma protuberans, but nonetheless have an important presence in children, even as a congenital neoplasm. A lipomatous tumor in a young child should be considered as a possible manifestation of an overgrowth syndrome.