Introduction
UPS, formerly known as malignant fibrous histiocytoma (MFH), is a high grade pleomorphic neoplasm without any definable line of differentiation1. UPS usually occurs in the extremities or retroperitoneum, and primary tumors of the gastrointestinal tract are uncommon. Only 14 cases of cecal or ascending colon UPS are reported in the literature. The classification and subdivision of these tumors went through several iterations until the WHO 2002 classification eliminated the term MFH and replaced it with UPS1.
UPS are most common later in life, usually the 6th and 7th decades2, and account for roughly 20% of all soft-tissue sarcomas3, 4, 5. UPS are more common in men than women with a 2.4:1 ratio6.
Risk factors for the development of UPS include genetics, radiation or chemotherapy exposure, chemical carcinogens, chronic postoperative repair, trauma, surgical incisions and lymphedema6, 7.The cellular origins of UPS are unclear, but possibly arise from primitive mesenchymal stem cells that retain both fibroblastic and histiocytic potential and may present with markers and behaviors of both cell lines8, 9.
UPS typically presents as an enlarging lump that is often excised early when located on an extremity. Unfortunately, intestinal UPS is often discovered late with substantial tumor bulk. Presenting symptoms may include abdominal distention and pain, altered bowel habits, weight loss, anemia, blood in the stool, or palpable abdominal mass. Compared to other types of colon cancer, UPS presents more frequently with a right sided mass, less frequently with constipation, and in up to 25% of cases patients report fevers9. Labs at diagnosis may be normal, or may show elevated inflammatory markers, leukocytosis, and anemia.
Diagnosis is based on a combination of microscopic features and immunohistochemical staining techniques used to rule out other cell lines of origin. Lesions are typically characterized by pleomorphic, spindle-shaped cells with bizarre cytology and nuclear atypia10. Immunohistochemical staining is sometimes positive for vimentin, actin, CD68, alpha 1-antitrypsin, alpha 1-antichymotrypsin, and laminin mRNA3, 10. Importantly, UPS has no reproducible immunophenotype or pattern of protein expression that allows for further classification of the tumor3 and exclusion of pleomorphic variants of other neoplastic lines is required5.
CT imaging typically shows a well-circumscribed and homogeneous mass, or a low-density mass secondary to necrosis and hemorrhage10. Masses are sometimes large and lobulated, and may also have calcifications, hemorrhage, myxoid degeneration, necrosis, or tissue invasion3.
Standard treatment for UPS is early complete surgical resection with negative resection margins and en-bloc lymph node dissection. The role of chemotherapy and radiation in the treatment of UPS is debated and without strong evidence. Increasing number of reports suggest that adjuvant chemo or radiation may improve prognosis in certain clinical scenarios4, 10. Data from large studies on outcomes with different treatments is limited and most reported cases of intestinal UPS were treated with surgery alone.
Prognosis for UPS is generally poor because of regional invasiveness, distant metastases and frequent recurrence6. A review of 200 cases found that the 2 year survival rate was 60%, 5 year survival rate 47%, and overall recurrence rate 44%. Metastasis occurred in 42% of cases, most commonly to the lungs (82%) but also to lymph nodes (32%)2.