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.