[4] PF/PM lesions have been regarded as a tissue's self-limiting reaction to an injury or unidentified insult rather than an abnormal growth of a clone of neoplastic cells, that is, as a group of cells which share a common ancestry, have similar abnormalities in the expression and/or content of their genetic material, and often grow in a continuous and unrestrained manner.

[6] PF/PM lesions may grow at alarming rates,[3] exhibit abnormal histopathologies (e.g. high numbers and overcrowding of cells), and have other elements that are suggestive of a malignancy.

[6] PF/PM lesions occur primarily in middle-aged and older adults[6] (peak age of onset 50 to 55 years/old) with no appreciable differences in their incidences between males and females.

[1] Individuals commonly present within 1–3 weeks[1] or, rarely, longer times (e.g. 3 months)[8] of noticing a rapidly growing, small (<5 cm.

in size) mass or swelling in the subcutaneous tissues or muscles[1] of an extremity or, less commonly, the trunk wall, head, or neck areas.

[2] Overall, the cells in these lesions are amphophilic or basophilic, may have vacuole-laden cytoplasm, are slowly multiplying based on their proliferative index, and lack atypical mitosis figures that might be suggestive of a malignancy.

[8] A recent study conducted in Japan found that the tumor tissues of 5 of 5 analyzed adult patients with PF/PM lesions expressed a high level of an abnormal c-Fos protein.

The FOS:VIM fusion gene along with its c-Fos-VIM protein (which possesses uncontrolled c-Fos activity) are associated with the development and/or progression of some other fibroblastic and myofibroblastic tumors as well as malignant sarcomas.

Symptomatic therapy such as analgesics, e.g. nonsteroidal anti-inflammatory drugs, may be required to treat pain or rare cases of fever.