DFSP tumors typically consist of bland-appearing, slowly proliferating, spindle-shaped cells arranged in a monotonous cartwheel or whorled pattern.
[15] The initial lesions in DFSP and DFSP-FS typically begin as small, single, painless, violet or pink cutaneous nodules or plaques (i.e. elevated areas of skin 2 cm.
About 10[13] to 15%[1] of individuals initially or subsequently present with metastases,[2] most commonly in the lung, less commonly in the regional lymph nodes draining the site of the primary dermal tumor,[13] or, rarely, in the liver, kidney, soft tissue sites outside of the primary dermal tumor's areas,[3] mediastinum, or brain.
The COL1A1 gene, which directs production of collagen, type I, alpha 1 protein, is normally located in band 21.33 on the long (or "q") arm of chromosome 17.
[21] The PDGFB gene, which directs production of platelet-derived growth factor subunit B (PDGFβ) protein, is normally located in band 13.1 on the q arm of chromosome 22.
[1] The overproduced PDGFβ proteins bind to platelet-derived growth factor receptors to promote these receptors' intrinsic tyrosine kinase activity and thereby to overstimulate mitogen-activated protein kinases, PI3K/AKT/mTOR, and other cell signaling pathways which promote the growth, proliferation, and prolonged survival of their parent cells.
[8] Further studies are needed to determine the latter five fusion genes' prevalence in, and contribution to the development and/or progression of, DFSP and DFSP-FS.
The diagnosis of DFSP-FS depends on finding a dermal tumor with characteristic areas consisting of spindle-shaped cells with atypical, vesicular nuclei aligned in smooth muscle-like bundled[8] or herringbone patterns.
[2] Tumors located on a finger or toe, which trend to have a high and rapidly developing recurrence rate, may be treated by partial or total amputation.
[16] Tumors that are only partly resectable have been treated with partial resection combined with radiotherapy, drugs that inhibit the tyrosine kinase on the platelet-derived growth factor receptors stimulated by DFSP-FS (in cases where the tumor cells express the COL1A1-PDGFB fusion gene),[8] and/or, in rare cases, chemotherapy regimens.
Sunitinib, which inhibits various types of tyrosine kinases, has been used as a second-line agent for the treatment of imatinib-resistant tumors: 30 patients who developed resistance to imatinib had an 80% overall rate of disease control in response to this drug.
[20] Retrospective reviews of patients treated for DFSP-FS find average 5-year recurrence-free survival rates of 42%-52% with a 10%-15% risk of having or developing metastatic disease.