Abstract
The classification of soft tissue tumors has evolved considerably in the last decade, largely due to advances in understanding the pathogenetic basis of many of these, sometimes rare, tumors. Deletion of Retinoblastoma 1 (RB1), a well-known tumor suppressor gene, has been implicated in the tumorigenesis of a particular group of soft tissue neoplasms. This group of so-called “RB1-deleted soft tissue tumors” has been rapidly expanding in recent years, currently consisting of spindle cell/pleomorphic lipoma, atypical spindle cell/pleomorphic lipomatous tumor, pleomorphic liposarcoma, myofibroblastoma, cellular angiofibroma, and acral fibromyxoma. Most of these neoplasms, except pleomorphic liposarcoma, are considered benign entities and are mainly described in the older adult population. This article will review the currently known morphological, immunohistochemical, and molecular features of this heterogeneous group of mesenchymal tumors with an emphasis on differential diagnosis.
Highlights
Variable fibromyxoid stroma, ropey collagen, mast cellsVariable fibromyxoid stroma, ropey collagen, mast cells, perivascular lymphocytic infiltrateHighly cellular with scant fibromyxoid stromaFibrous stroma with variable hyalinized areas, ropey collagen, mast cells, perivascular lymphocytic infiltrateVariably edematous and fibrous stroma, sometimes myxoid change, mast cells, perivascular lymphocytic infiltrateVariably myxoid stroma with fibrous areas, mast cells Cellularity Low Highly variable High Low to moderate
Retinoblastoma 1 (RB1)-deleted soft tissue tumors are most-commonly seen in the older adult population, usually in patients older than 50 years of age
Information concerning the anatomic location of an RB1-deleted soft tissue tumor may be crucial in making the correct diagnosis, especially as some of these tumors occur almost exclusively in particular anatomic regions
Summary
RB1-deleted soft tissue tumors are most-commonly seen in the older adult population, usually in patients older than 50 years of age. They can be encountered in a wide variety of anatomical sites. Information concerning the anatomic location of an RB1-deleted soft tissue tumor may be crucial in making the correct diagnosis, especially as some of these tumors occur almost exclusively in particular anatomic regions. This is the case, for example, with acral fibromyxoma and cellular angiofibroma, which typically occur in sub (peri-)ungual and inguinal locations, respectively.
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