Solitary fibrous tumors are rare growths of soft tissue cells that can form nearly anywhere in the body.

Solitary fibrous tumors most often occur in the lining around the outside of the lungs (pleural solitary fibrous tumors). Solitary fibrous tumors have also been found in the head and neck, breast, kidney, prostate, spinal cord, and other sites.

Most solitary fibrous tumors are noncancerous (benign), but in rare cases, solitary fibrous tumors can be cancerous (malignant). Solitary fibrous tumors tend to grow slowly and may not cause signs and symptoms until they become very large.