fibrosarcoma
Meaning of fibrosarcoma: A diagnosis that has shrunk as laboratory testing improved, since most tumors once given the name proved to be something else.
Definition of fibrosarcoma
Fibrosarcoma is a malignant tumor of fibroblasts, the cells that build the fibrous scaffolding holding muscles, bones and organs in position. Under the microscope it forms sheets of long spindle-shaped cells laid in intersecting bundles. It can arise wherever fibrous tissue exists, most often deep within a limb or the trunk, and it is now diagnosed only once other tumors that look similar have been excluded.
Why has the diagnosis become rarer?
Not because the tumor changed, but because the tools did. Spindle-shaped cells packed in bundles look much alike whatever their origin, and for a long time appearance under the microscope was all there was to judge by, so a whole family of tumors was swept under one name. Staining for particular proteins and testing for particular gene rearrangements have since pulled that family apart. Tumors once called fibrosarcoma are now recognized as nerve sheath tumors, as synovial sarcoma, as a fat-derived tumor that has lost any resemblance to fat, or as a tumor of the membranes lining tissue spaces. What is left is a diagnosis of exclusion, reached when nothing else fits.
How do the adult and infant forms differ?
| Feature | Infantile form | Adult form |
|---|---|---|
| Usual age | The first year of life | Middle and later adult life |
| Underlying change | A single fusion of two genes | Varied and complex changes |
| Behavior | Grows locally, rarely spreads | Can spread through the bloodstream |
| Drug options | Responds to drugs aimed at the fusion | No single target to aim at |
The infantile form shows a name outliving its usefulness. It shares an appearance with the adult tumor and almost nothing else, and the fused gene it carries also turns up in a salivary gland tumor and in one kidney tumor of infancy, all of which answer to the same class of drug.
Where does it sit among the sarcomas?
Within the large group of soft tissue sarcoma, cancers growing out of the body's supporting tissues rather than from the linings and glands that give rise to the far commoner carcinomas. Its parent tissue is connective tissue: the fibers and packing material holding structures in place. Because these tumors grow in the depths of a limb rather than at a surface, they are often sizeable before anyone notices, and a firm painless lump lying beneath muscle is the usual first sign. The elongated cells arranged in a herringbone pattern place it among the spindle cell sarcoma group on appearance alone, which is precisely the problem the modern tests were built to solve.
Used in a sentence
Fibrosarcoma was reported once immunostaining had excluded the other spindle cell tumors.
Good to know
Fibrosarcoma has become largely a diagnosis of exclusion, since staining and gene testing reassign most tumors that once carried the name, and the infantile form is a distinct disease that behaves far less aggressively than the adult one.
Word origin
Where “fibrosarcoma” comes from
Fibro- comes from the Latin fibra, meaning fiber. Sarcoma comes from the Greek sarx, meaning flesh, with the ending -oma marking a growth, and names tumors of the body's supporting tissues.