NF tumors, which may be tender or painful, typically present as rapidly growing solitary lesions that reach their final size (usually 2–3 cm) within a few weeks.

Individual cases of NF have been reported to occur in the bladder, prostate, tongue, lower female genital tract, and parotid gland.

Individual cases have been reported to occur in the lower jaw, frontonasal region, anterior nasal spine, the orbit, and maxilla.

Characteristically, the tumor is rapidly enlarging, non-painful, rarely regressing without treatment, and potentially expanding into the skull's interior.

The tumors originate in the small blood vessels of the oral mucosa, eyes, lips, cheeks, tongues, and subcutaneous tissue of the extremities (78% of all cases).

Most cases involving superficial sites present with a small (mean diameter of 1.5 cm), painless, slowly growing mass.

[6] The microscopic histopathology of hematoxylin and eosin stained nodular fasciitis tumors consists of spindle-shaped myofibroblastic cells.

These cells may show high rates of replicating as judged by their mitotic index, but these mitoses are normal in appearance.

[4] The histopathology and expressions of marker proteins in cranial fasciitis tumors tend to be more organized and have higher levels of inflammatory cell infiltrates, vascularity, and involvements of underlying bone than NF.

[13] The histopathology and expressions of marker proteins in intravascular fasciitis tumors tend to be arranged in a storiformed or haphazard pattern and have vesicle-containing nuclei with prominent nucleoli.

[15] However, recent findings indicate that up to 92% of NF tumors involve the self-limiting growth of a clone of neoplastic cells that contain a fusion gene.

[10] Further studies are needed to determine which, if any, of these pathways are overactive and can be successfully targeted with specific drug therapies to treat NF and its variants.

[10][25][26] NF may resemble and therefore be misdiagnosed as dermatofibrosarcoma protuberans, fibrosarcoma, malignant fibrous histiocytoma, spindle-cell melanoma,[27] leiomyosarcoma,[4] or inflammatory myofibroblastic tumor.

[8] While virtually all cases of NF and variants have had excellent prognoses, the two cases of individuals with an USP6-PPP6R3 fusion gene in their NF tumor cells had less favorable prognoses: their tumors were locally invasive, repeatedly relapsed after surgical removal, and grew progressively larger over 2 and 10 years of observations.