Haemosiderotic Fibrolipomatous Tumor

Not clinically relevant

Cytogenetic analysis has shown near-diploid karyotypes with balanced or unbalanced t(1;10)(p22-p31;q24-q25), loss of material from 3p, and amplification of 3p11-p12. The t(1;10) does not result in a fusion transcript but always targets TGFBR3 in 1p22, demonstrates breakpoints in or near OGA (formerly MGEA5) in 10q24, and leads to transcriptional upregulation of neighboring FGF8 and NPM3. The t(1;10) has been found in as many as 85% of HFLTs. The amplicon in 3p contains VGLL3 and CHMP2B, which show increased expression. Similar karyotypes, rearrangement of TGFBR3 and OGA, and amplification of VGLL3 have also been observed in myxoinflammatory fibroblastic sarcoma and pleomorphic hyalinizing angiectatic tumor of soft parts, suggesting a pathogenetic link between these entities. BRAF fusions are present in some myxoinflammatory fibroblastic sarcomas, but they have not been detected in HFLT.

Tumor size averages 7.7 cm but can reach as large as 19 cm. HFLT is poorly circumscribed, dark yellowish-brown, and friable, with occasional hemorrhage.

HFLT consists of lobules of mature fat admixed in variable proportions with fascicles of fibroblastic spindle cells containing haemosiderin, haemosiderin-laden macrophages, and osteoclast-like giant cells. In areas, the spindle cells are distributed more loosely in smaller numbers and often extend between individual adipocytes and around vessels. Occasional larger cells with atypical nuclei are sometimes present. Mitotic activity is low and necrosis is absent. Nuclear pseudoinclusions and large, ectatic, partially thrombosed vessels with perivascular hyalinization are sometimes present, leading to morphological overlap with pleomorphic hyalinizing angiectatic tumor. Areas resembling HFLT may be observed at the edge of pleomorphic hyalinizing angiectatic tumor. Rare cases of HFLT may unpredictably recur as myxoid sarcoma with histological features of hybrid HFLT–myxoinflammatory fibroblastic sarcoma. The spindled cells of HFLT are usually positive for CD34 and calponin.

Aspirates typically show a variably cellular mixture of mature adipose tissue and bland, monotonous spindle cells, a subset of which contain haemosiderin, along with haemosiderin-laden macrophages.

The local recurrence rate is 30–50%, especially if the tumor is incompletely excised. The recurrence rate can be reduced by complete surgical resection. Metastases have not been reported in pure HFLT, but rare tumors with transformation to sarcoma may result in distant metastasis.

Demonstration of t(1;10)(p22;q24) or OGA and TGFBR3 rearrangement may be helpful.

Essential: mature adipose tissue admixed with bland haemosiderin-laden spindle cells and macrophages.

Desirable: demonstration of t(1;10)(p22;q24), OGA, and/or TGFBR3 rearrangement (in selected cases).