<unk>  (DFSP-FS), also termed<unk> <unk><unk> , is a rare type of tumor located in the dermis (i.e. layer of the skin below the epidermis). DFSP-FS tumors have been viewed as: 1) a more aggressive form of the<unk><unk>  (DFSP) tumors because they have areas that resemble and tend to behave like malignant fibrosarcomas or 2) as a distinctly different tumor than DFSP. DFSP-FS tumors are related to DFSP. For example, surgically removed DFSP tumors often recur with newly developed fibrobosarcoma-like areas. Nonetheless, the World Health Organization (WHO), 2020, classified DFSP and DFSP-FS as different tumors with DFSP being in the category of benign and DFSP-FS in the category of rarely metastasizing fibroblastic and myofibroblastic tumors. This article follows the WHO classification: the 5-15% of DFSP tumors that have any areas of<unk>  microscopic histopathology are here considered DFSP-FS rather than DFSP tumors. DFSP tumors typically consist of bland-appearing, slowly proliferating, spindle-shaped cells arranged in a monotonous cartwheel or whorled pattern. DFSP-FS tumors consist of less bland-appearing spindle-shaped cells that are arranged in fascicular (i.e. bundled, smooth muscle-like) or herringbone-like patterns, have large, vesicular, misshaped nuclei, and are rapidly proliferating; these DFSP-FS areas are typically but not always admixed with DFSP areas. Various studies find that DFSP-FS tumors have higher rates of recurrence after surgical removal than DFSP tumors and may metastasize (i.e. spread to distant tissues). The tumor cells in DFSP and DFSP-FS harbor one or more fusion gene mutations, i.e. mutations that merge two previously independent genes. The COL1A1-PDGFB fusion gene is the most common fusion gene found in both tumor types. However, DFSP-FS tumor cells have higher copy numbers of the COL1A1-PDGFB fusion gene than do DFSP tumors. Localized DFSP-FS tumors are typically treated by wide surgical excision in order to reduce the high recurrence rates developing when these tumors' cells are not completely removed. Adjuvant therapy (i.e. therapy given in addition to the primary or initial therapy in order to maximize its effectiveness) consisting of radiation therapy and/or drugs (i.e. protein kinase inhibitors that block the effects of the COL1A1-PDGFB fusion gene) may be added to the treatment regimen in cases where a tumor cannot be fully removed and in virtually all cases where the tumor has metastasized.
Dermatofibrosarcoma protuberans, fibrosarcomatous
Lymphoepithelioma-like carcinoma
Basal-like carcinoma
Mammary-type myofibroblastoma
Sclerosing epithelioid fibrosarcoma
Low-grade fibromyxoid sarcoma
Melanoma with features of a Spitz nevus
Neural fibrolipoma