Lipoblastomas presenting in older children and adults: analysis of 22 cases with identification of novel PLAG1 fusion partners.

Lipoblastomas are benign neoplasms of embryonal white fat that typically present in the first 3 years of life and show a lobular arrangement of maturing adipocytes with variable degrees of myxoid change. We systematically studied the clinicopathologic and genetic features of lipoblastomas arising in older children and adults. Cases with a diagnosis of lipoblastoma or maturing lipoblastoma in patients >3 years of age were retrieved from our archives. Immunostaining for CD34 and desmin and molecular studies (FISH, RNA sequencing) were performed. Twenty-two cases (8F; 14M) were identified in patients ranging from 4 to 44 years of age (median 10 years). Sites included extremity (n = 15), head and neck (n = 4), and trunk (n = 3) with tumor sizes varying from 1.6 to 17.5 cm (median 5). Only three tumors had histologic features of "conventional" lipoblastoma. The majority of tumors (n = 14) were composed of variably sized lobules of mature adipose tissue partitioned by thin fibrous septa ("maturing"). The remaining five cases consisted predominantly of bland spindled to plump ovoid cells embedded in a fibrous stroma, with a vaguely plexiform arrangement of small myxoid and adipocytic nodules ("fibroblastic"). CD34 was diffusely positive in all cases tested (21/21), while desmin immunoreactivity was identified in 12 of 21 cases (diffuse = 7, focal = 5). PLAG1 rearrangements were identified in 13 tumors in the entire cohort (59%), including all 5 fibroblastic tumors. RNA sequencing detected eight PLAG1 fusion partners, of which two were known (CHCHD7 and COL3A1) and six were novel (SRSF3, HNRNPC, PCMTD1, YWHAZ, CTDSP2, and PPP2R2A). Twelve cases had follow-up (1-107 months; median 21 months), and no recurrences were reported. Lipoblastomas may occur in older children and adults and may be difficult to recognize due to their predominantly adipocytic or fibrous appearance. Awareness that lipoblastomas may occur in older patients, careful evaluation for foci showing more typical morphologic features, ancillary immunohistochemistry for CD34 and desmin, and molecular genetic studies to identify PLAG1 rearrangements are the keys to recognizing these tumors.

Analysis of clinical features of lipoblastoma in children.

OBJECTIVE: A lipoblastoma is pathologically benign but often recurs. Due to its rarity, studies are scarce. The purpose of this study was to investigate the clinical characteristics of lipoblastoma occurring in children and to detect any correlations with the expression of Ki-67. PARTICIPANTS: From 1998 to 2010, 33 patients were diagnosed with lipoblastoma at Seoul National University Children's Hospital. METHODS: Ki-67 immunohistochemistry staining of the tumor tissue was performed. RESULTS: A total of 33 patients (64% males) were enrolled in the study, with a mean age of 28 month. Eleven and 22 lesions were deep and superficial, respectively. Complete excisions were performed for 30 patients, and three underwent incomplete excisions. Two patients who underwent incomplete excision subsequently underwent a second operation due to tumor regrowth, and one patient had a recurrence despite complete excision. There was no statistically significant correlation observed between the tumor size or recurrence and the expression of Ki-67. CONCLUSIONS: Lipoblastoma requires an accurate diagnosis and operative resection to alleviate the symptoms induced by its growth. Incompletely resected tumor may regrow; therefore, complete excision is the treatment of choice. Continuous follow-up is needed to monitor for recurrence of disease, even after a complete excision.

Varied Presentations of Pediatric Lipoblastoma: Case Series and Review of the Literature.

Lipoblastoma is a rare neoplasm of embryonal adipose tissue most often encountered on the trunk and extremities of children. It commonly presents as a painless subcutaneous soft tissue mass, but there are other unique clinical presentations that are important to recognize. The differential is broad and includes sarcoma, vascular tumor, myofibroma, and other fibromatoses. We present three varied, distinct cases of pediatric lipoblastoma and review the literature on this condition.