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Case of the Month




Plantar Fibromatosis
July, 2020
A 49 year old woman presents with solitary painful subcutaneous nodule located in the plantar surface of the right foot. The lesion is fairly circumscribed. The patient undergoes excisional biopsy. An excisional subcutaneous ill-defined lesion is seen on gross examination (3.0 x 2.5 x 1.5 cm). Microscopic evaluation demonstrates a spindle cell proliferation with associated areas of hemorrhage. The spindle cells show a long sweeping fascicular arrangement with smooth nuclear borders with prominent vasculature. There is minimal background inflammation. No significant mitotic figures, cellular atypia or necrosis is identified. To further characterize these cells immunohistochemical stains performed and the results are as follows:
CK-pan: Negative in lesional cells

S100: Negative in lesional cells

CD34: Negative in lesional cells

Beta-catenin: Positive nuclear staining in lesional cellsĀ 

These findings support a diagnosis of plantar fibromatosis. This condition consists of a nodular myofibroblastic proliferation of the plantar surface of the foot that is prone to local persistence but does not metastasize. The incidence is 1-2 per 100,000 persons per year (Northern Europe), most patients 30-50 years of age with a slight male predominance. Superficial fibromatoses present as nodular lesions on palms, soles, knuckles, or penis. Superficial fibromatoses are treated by excision. Recurrences are common for both superficial and deep lesions.


  1. Bhattacharya B et al: Nuclear beta-catenin expression distinguishes deep fibromatosis from other benign and malignant fibroblastic and myofibroblastic lesions. Am J Surg Pathol. 29(5):653-9, 2005
  2. Cates JM et al: Surgical resection margins in desmoid-type fibromatosis: a critical reassessment. Am J Surg Pathol. 38(12):1707-14, 2014