Background

This soft tissue tumor has been proposed as a name that encompasses several rare soft tissue pediatric neoplasms. Tumors which have previously been interpreted or diagnosed as infantile or juvenile fibromatosis, a variant of fibrous hamartoma of infancy, and a fibrosing lipoblastoma may be grouped under this diagnosis.

INCIDENCE	Rare-45 cases reported
AGE RANGE-MEDIAN	11 days to 12 years Median 1 year
SEX (M:F)	32 males 12 females

 

HISTOLOGICAL TYPES	CHARACTERIZATION
General	Abundant adipose tissue with a spindled fibroblastic element that chiefly involved the septa of the fat and skeletal muscle Generally did not cause extensive architectural effacement of fat and did not have the primitive nodular fibromyxoid component of fibrous hamartoma Fibroblastic element had focal fascicular growth with limited mitotic activity (<1/10 hpf) and limited cytologic atypia Small collections of univacuolated cells were present at the interface between some of the fibroblastic fascicles and mature adipocytes Tumors entrapped vessels, nerves, skin adnexa, and skeletal muscle
A Clinicopathologic Study of 45 Pediatric Soft Tissue Tumors With an Admixture of Adipose Tissue and Fibroblastic Elements, and a Proposal for Classification as Lipofibromatosis John F. Fetsch, M.D.; Markku Miettinen, M.D.; William B. Laskin, M.D.; Michal Michal, M.D.; Franz M. Enzinger, M.D.	Am J Surg Pathol 2000;24:1491-1500 Abstract quote The tumor described here as lipofibromatosis is a rare pediatric neoplasm that has been variously interpreted as a type of infantile or juvenile fibromatosis, a variant of fibrous hamartoma of infancy, and a fibrosing lipoblastoma. This report details the clinicopathologic features associated with 45 cases of this soft tissue entity. The study group consisted of 32 males, 12 females, and one person of unstated gender. The patients presented with a soft tissue mass (range, 1–7 cm) involving the hand (n = 18), arm (n = 8), leg (n = 7), foot (n = 6), trunk (n = 5), or head (n = 1). Eight tumors were evident at birth. The individuals ranged in age from 11 days to 12 years (median age, 1 yr) at the time of initial biopsy or resection. Microscopic examination revealed abundant adipose tissue with a spindled fibroblastic element that chiefly involved the septa of fat and skeletal muscle. The process generally did not cause extensive architectural effacement of fat as is common with conventional fibromatoses, and it did not have a primitive nodular fibromyxoid component as is characteristic of fibrous hamartoma of infancy. The fibroblastic element exhibited focal fascicular growth and typically had limited mitotic activity (1 mitosis/10 high-power fields) and cytologic atypia. Oftentimes, small collections of univacuolated cells were present at the interface between some of the fibroblastic fascicles and the mature adipocytes. The tumors entrapped vessels (n = 45), nerves (n = 44), skin adnexa (n = 16), and skeletal muscle (n = 18). Focal immunoreactivity was present in some tumors for CD99, CD34, -smooth muscle actin, BCL-2, and less frequently, S-100 protein, muscle actin (HUC 1-1), and EMA. However, no reactivity was detected for desmin (D33 and D-ER-11 clones), keratins, or CD57. Follow-up data were available for 25 individuals (median follow-up period, 6 yrs 7 mos) with regrowth of the tumor or persistent disease documented in 17 (72%). The following events were more common in the group with recurrent or persistent disease: congenital onset, male sex, hand and foot location, incomplete excision, and mitotic activity in the fibroblastic element. Although it is likely this tumor comprises part of the spectrum of what has been referred to in the literature as infantile/juvenile fibromatosis, its clinicopathologic features and, in particular, its distinctive tendency to contain fat as an integral component, warrant separate classification as a ``lipofibromatosis.''

 

SPECIAL STAINS/IMMUNOPEROXIDASE/OTHER	CHARACTERIZATION
Special stains
Immunoperoxidase	Focal positivity for: CD99 SMA bcl-2 Less frequent positivity for: S100 Muscle actin EMA Negative for: Desmin Keratins CD57

 

PROGNOSIS AND TREATMENT	CHARACTERIZATION
Prognostic Factors	Poor factors include: Congenital onset Male sex Hand and foot location Incomplete excision Mitotic activity in the fibroblastic element
Recurrence	Regrowth of tumor or persistent disease in 17/25 (72%)

Am J Surg Pathol 2000;24:1491-1500.

Soft tissue tumors

Last Updated 12/12/2000

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