Soft Tissue Sarcoma (STS) is a group of different neoplasms with variable characteristics and different types of cells affected. It arises from soft tissues, such as muscle, fat, nerves, blood vessels, fibrous tissues, or deep skin tissues. It may arise anywhere in the human body with limbs being the most common site. There are many different types of soft tissue tumors (abnormal growth of cells that remain confined to the site of origin) which are about 100 times more common than the STSs. Benign soft tissue tumors, such as fibroma, hemangioma, lipoma, leiomyoma, lymphangioma, myxoma, neurofibroma, neuroma, schwannoma, rhabdomyoma, and others are not discussed here.
Types of Soft Tissue Sarcoma
Liposarcoma is cancer that arises from the adipose (fatty) tissue anywhere in the body. It accounts for about 20% of all STSs in adults. Most common location of liposarcoma includes thigh, behind the knee, and retroperitoneal (backside of the abdomen). It mostly occurs in individuals aged 50 to 65 years.
Liposarcoma can be further divided into 3 subgroups:
Well-differentiated and dedifferentiated
Well-differentiated liposarcoma is generally present as a deep-seated, painless, enlarging mass that may become very large over time but does not spread to a distant location. It has a good prognosis for limbs but a poor prognosis for retroperitoneum or mediastinal location. Dedifferentiated liposarcoma is characterized by the presence of non-lipogenic area(s) within the tumor.
It is considered as a high-grade tumor that usually consists of small, evenly dispersed round cells with a variable number of fat cells. Greater the number of round cells more aggressive is the disease.
It is a high-grade tumor that consists of different lipoblasts, tends to spread quickly to lungs and has a worse prognosis.
It arises from the fibrous tissue anywhere in the body, especially that of limbs, trunk, and head and neck region. It is relatively uncommon, accounting for about 1% of all STSs in adults. It mostly affects middle-aged and older adults with a few cases reported in children. It shows moderate aggressiveness with little tendency to spread to nearby tissues.
LMS mainly arises from the smooth muscles in the blood vessels, uterus, and other visceral organs/structures. They mostly affect middle-aged or older adults with the most common location being the smooth muscles of the large blood vessels in the retroperitoneum/abdomen or in the pelvis, especially uterus. It may occur anywhere in the body and presentation depends upon the type of tissue involved. When a blood vessel is involved, obstruction in the blood flow is common, with pain due to the involvement of the nearby nerves. Large size tumors and high-grade disease usually have a poor prognosis.
RMS mainly arises from the skeletal muscles (voluntary muscles that control the body movement at will). RMS cells resemble cells those are formed during an early phase of development in a 6- to 8-week old embryo and eventually give rise to skeletal muscles. It generally affects children with a few cases reported in adults. It can occur anywhere in the body.
RMS can be categorized into the following 3 subtypes:
It is the most common subtype that mainly affects the children less than 5 years of age with a few cases reported in adults. The most common locations include orbit (eyeball), head and neck area, bladder, vagina, prostate, and testicles.
It generally affects skeletal muscles of the limbs and trunk in adolescents and young adults. These are rare in younger children and have poor prognosis in this population
Anaplastic or Pleomorphic RMS
It is an inherently aggressive disease that mostly affects adults.
It may arise either from the blood vessels (hemangiosarcomas) or from lymph vessels (lymphangiosarcomas). Most angiosarcomas start in the superficial soft tissues including skin with less than one-fourth starting in the deeper soft tissues. The incidence of these tumors has been linked with the history of radiation treatment, especially in the breast where these tumors generally occur after initial radiation therapy along with lymphedema. These tumors generally have a poor prognosis.
It arises from the cells lining the blood vessels and lymph vessels. It may develop anywhere in the body including the lymph nodes and visceral organs like lungs and those of digestive system. It mostly presents as a dark-colored, irregular tumor on the skin or on the mucosa of the mouth. It can be life-threatening when it involves visceral organs.
KS can be further divided into four classes:
t is the most common type of KS in the US. It occurs in individuals with AIDS, that is, when the immune system has been severely compromised due to the HIV infection.
It is mostly reported in Mediterranean, Eastern European, and Middle Eastern countries. It does not require prior significant immunosuppression and is mostly observed in old-aged individuals with relatively higher incidences reported in males. It usually presents as single or multiple tumors in the lower limbs.
It is common among individuals living in the Equatorial African countries. It mostly affects young adults and children. In children before attaining puberty, KS may occur as an aggressive form affecting lymph nodes. KS-related herpes virus infection is more common in Africa.
It is observed in individuals with a suppressed immune system due to a prior organ/hematopoietic stem cell transplant and who are on immunosuppressants.
GASTROINTESTINAL STROMAL TUMOR (GIST)
GISTs arise from the interstitial cells of Cajal (ICC) in the gastrointestinal (GI) tract. The ICC are a part of the autonomous nervous system that regulate the smooth muscles in the GI tract. Thus, they are sometimes referred to as pacemaker of the GI tract. GISTs may occur anywhere in the GI tract with the stomach being the most common site, followed by the small intestine. They may even start outside of the GI tract, such as the tissue in the vicinity of the digestive system, e.g. the omentum or peritoneum. They are rare and mostly affect old-aged individuals. They show variable behavior in different individuals, and may spread to nearby and distant body parts.
ALVEOLAR SOFT PART SARCOMA (ASPS)
It generally arises from the soft tissues in the lower limbs of young adults. It is a rare type of sarcoma accounting for less than 1% of all STSs. It generally presents as a painless slow-growing mass without any other symptom but can spread readily to distant body parts, causing a poor prognosis.
It generally arises from the tissue under the skin of upper and lower limbs in adolescent and young adults. The lesions are multinodular with a central region of tissue necrosis. These cancers can spread to lymph nodes and generally have a poor prognosis.
It arises from the fibrous tissue, with a variable myxoid component. It mostly presents as a painless mass in the limbs and/or trunk. It generally occurs as a low-grade disease that can progress to a high-grade variant, that may spread to lungs, lymph nodes, and bones.
MALIGNANT PERIPHERAL NERVE SHEATH TUMOR (MPNST)
This arises from the nerve sheath rather than from the nerve itself. It mostly affects the major nerves of the body, especially those in the lower limbs and the trunk of middle-aged adults. Most of these tumors are high-grade with a high tendency to spread to distant body parts.
It arises from osteoid cells not attached to the s keleton. The most common location for extraskeletal osteosarcoma is limbs with few cases reported in breast, urinary bladder, retroperitoneum, and other visceral organs. It mostly affects individuals older than 50 years.
Synovial sarcoma arises from deep soft tissue (not necessarily the synovial tissue) around the joints – hip, knee, ankle, and shoulder. It generally affects males aged between 15 to 35 yers. It is presented as a slow-growing painful (or sometimes painless) mass and can spread to nearby tissues.
CLEAR CELL SARCOMA
It mostly affects tendons in the lower and upper limbs of young adults and present with a painful or painless soft tissue mass composed of epithelioid-type cells that behave like melanoma (cancer of melanin-producing skin cells). The tumor cells contain melanin and tend to spread to nearby lymph nodes. Clear cell sarcoma cells typically contain translocation t(12;22) resulting in fusion of the EWSRI and ATF1 genes.
UNDIFFERENTIATED PLEOMORPHIC SARCOMA (UPS)
It usually presents as a painless, deep-sited tumor that can grow locally and can spread to nearby tissues. It mostly affects individuals in their 60s. The most common loc ation is limbs and retroperitoneum.
DESMOPLASTIC SMALL ROUND CELL TUMOR
It contains monotonous cells that are stained by hematoxylin or eosin stains. Translocation t(11;22) resulting in fusion of the EWSRI and WT1 genes is the characteristic feature of this tumor. It is mostly seen in children and young adults with abdomen being the most common location.
AGGRESSIVE FIBROMATOSIS/DESMOID TUMORS
These tumors arise from the fibrous tissue and have characteristics intermediate between fibrosarcoma and fibroma. These can spread to a nearby tissue with less chances of spread to a distant body parts. Abdominal wall (specifically after pregnancy), mesentery of the small intestine, and limbs are the most common location for these tumors. They generally present as a painful slowly growing mass that may cause compression of nearby structures or obstruction, depending upon their location.
DERMATOFIBROSARCOMA PROTUBERANS (DFSP)
It is the sarcoma of the fibrous tissue beneath the skin including both dermis and subcutis. It mostly affects individuals aged between 30 to 50 years. It shows an infiltrative pattern, and spreads locally with multifocal nodules. The skin of the limbs and the trunk is the most common location. It grows slowly but have high recurrence due to it’s infiltrative nature.
SOLITARY FIBROUS TUMORS (SFT)/HEMANGIOPERICYTOMA
It arises from the fibrous and/or fatty tissue and is characterized by the presence of branching vascular pattern within the tumor mass. It usually presents as a slow-growing painless mass in the thoracic cavity, retroperitoneum, pelvis, orbit, underarms and/or lower limbs. It mostly affects middle-aged adults, and is mostly benign but can be malignant. Previously called hemangiopericytomas, are now considered solitary fibrous tumors.
It is a tumor that arises in the blood vessels supplying to soft tissues or to internal organs, such as the liver or lungs. It is generally a slow-growing low-grade cancer that can spread to nearby tissues and sometimes to distant body parts.
After discussing the various types of soft tissue sarcomas, we will now understand their diagnostic investigations, risk factors, symptoms, staging, grading, risk stratification and treatment.
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