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What is sarcoma?

Sarcoma is the name given to a variety of cancers that arise from the bones and soft tissues, including fat, muscle and blood vessels. Bone sarcomas typically occur in children and adolescents, whereas soft tissue sarcomas are more common in adults.

What is different about sarcoma?

Sarcomas are very rare in comparison to carcinomas, which develop in the glands and organs of the body such as lung, breast and prostate. It is estimated that 12,000 new sarcomas occur annually in the United States out of a total of more than 1 million new cancer cases per year. Sarcoma represents 1% of all cancers in adults.

To add to the complexity of the disease, there are more than 70 subtypes of soft tissue sarcoma. All of the different subtypes of sarcoma are considered cancer; however, some subtypes of sarcoma are very slow growing and are almost benign, whereas others grow rapidly and are very aggressive. Some of the more common subtypes are:

  • Liposarcoma – originates from fat
  • Leiomyosarcoma – smooth muscle
  • Rhabdomyosarcoma – skeletal muscle
  • Angiosarcoma – blood vessel
  • Malignant peripheral nerve sheath tumor – covering around nerves
  • Synovial sarcoma – unknown tissue of origin (not from joint synovium)
  • Undifferentiated pleomorphic sarcoma – unknown tissue origin
  • Desmoid tumor – unknown tissue origin, likely scar tissue
  • Dermatofibrosarcoma protuberans – unknown tissue origin, likely from the skin

Knowing the exact subtype is important because it has implications for how the tumor will behave and sensitivity to various forms of treatment. Some subtypes and their unique features include:

  • Desmoid tumor – does not spread
  • Alveolar soft parts sarcoma – commonly spreads to the brain
  • Leiomyosarcoma – can spread to the skin
  • Myxoid liposarcoma – can spread to other fat-bearing areas
  • Well-differentiated liposarcoma – can have a distinct focal area of high-grade disease (dedifferentiated) within a larger low-grade tumor
  • Malignant peripheral nerve sheath tumor – can occur in patients with a hereditary syndrome called neurofibromatosis

With further research, we are identifying new subtypes (often based on unique tumor genetics, such as CIC-DUX4) and also defining subgroups within specific types.

Sarcomas are also different from carcinoma (and melanoma) in that they almost never involve the lymph nodes. There are exceptions to this — subtypes such as rhabdomyosarcoma, angiosarcoma, clear cell sarcoma, epithelioid sarcoma and synovial sarcoma can spread to the lymph nodes but frequently to other organ sites at the same time.

How and where does sarcoma appear?

Sarcoma can simply present as a new, painless lump. Pain can occur (for example, if the tumor is compressing a major nerve), but this is not common. Sometimes sarcomas do not cause any symptoms and are detected incidentally only when a patient sees a doctor for other issues. In general, a new mass that is large (>5 cm), deep in the body and undergoes rapid growth should raise suspicion for sarcoma; however, when in doubt any new mass should be evaluated.

Sarcoma can occur anywhere in the body. The most common location is in the legs and arms. About 20% of sarcomas appear in the back of the abdomen, which is also known as the retroperitoneum. Sarcomas in this location can frequently grow to a very large size before they are detected.

What causes sarcoma?

For the vast majority of sarcoma subtypes, the cause is unknown. There are specific hereditary cancer syndromes that predispose patients to developing sarcoma (for example, Li-Fraumeni), and prior radiation can be a risk factor for certain subtypes (for example, angiosarcoma of the breast). Importantly, current research suggests sarcoma is not linked to smoking, diet, obesity or specific lifestyle habits.

How is sarcoma diagnosed?

If you suspect you have a soft tissue sarcoma, your doctor may have you undergo an MRI or CT scan, followed by a biopsy. The MRI or CT scan should be done with contrast, which is especially important for surgical planning. Sometimes the characteristics of the tumor on MRI or CT scan alone can suggest the diagnosis and type of sarcoma. In most cases, however, a biopsy is needed to make a definitive diagnosis. This can be either a:

  • Core biopsy – The removal of a small amount of tumor tissue using a wide needle. This can be done as a minor procedure by a radiologist (sometimes guided by ultrasound or CT scan/MRI).
  • Incisional biopsy – The removal of part of a tumor through a minor surgery by a surgeon. This is often done if initial needle biopsy is inadequate.

A pathologist looks at the biopsy tissue under a microscope to look for cancer cells to make the diagnosis. The pathologist should state the specific subtype of sarcoma and can usually also determine the grade of the tumor. The grade of a tumor depends on how abnormal the cancer cells look under a microscope, for example how quickly the cells are dividing. High-grade tumors usually grow and spread more quickly than low-grade tumors.

Sarcoma can be hard to diagnose, and as a result, patients should ask to have their biopsy reviewed or rereviewed by a trained sarcoma pathologist. The correct diagnosis is critical to determine the appropriate treatment. Many benign diagnoses (for example, atypical lipoma) can also be confused with sarcoma. In some cases, if the diagnosis is unclear, the pathologist will perform further testing of the tissue to try to identify unique genetic features (for example, translocations, amplifications).

After the diagnosis of sarcoma, what else is needed?

Depending on the subtype, further studies may be needed to determine if the sarcoma has spread. This often includes a CT scan of the chest, as the most common location of spread is to the lungs. Occasionally, a whole body PET scan is done to simultaneously look at the lungs and other potential sites, such as the liver. A PET scan also provides additional information about tumor activity. This can be used to monitor response to treatment, for example, before and after drug therapy.

What is the treatment for sarcoma?

For sarcomas that have not spread, surgery is the main treatment. In the legs and arms, the standard of care is limb salvage as opposed to amputation. In the retroperitoneum, surgery often requires combined removal of the tumor with adjacent organs and structures (for example, a kidney). Sarcoma surgery in any body location may be challenging. “Margins” refers to normal healthy tissue that is removed with the tumor to try to ensure that all the disease is removed. In sarcoma, what is considered an adequate margin varies by subtype. Some subtypes require a wide margin, whereas for other subtypes this is not needed. Overall, to try to improve outcomes, chemotherapy and/or radiation therapy may be given in some cases either before (neoadjuvant) or after (adjuvant) the operation.

Patients with sarcomas that have already spread or that cannot be removed by surgery usually undergo systemic (or drug) therapy. This includes traditional cytotoxic chemotherapy. In the last few years, newer drugs have become available for sarcoma, including better targeted therapies and immunotherapy.

After treatment, what is my prognosis?

Staging systems, such as the AJCC TNM, 8th edition, and nomograms exist to help predict outcomes based on patient and tumor-related factors. The prognosis is very different for each individual patient and subtype of sarcoma. The prognosis also depends on the adequacy of treatment.

After treatment, what follow-up is needed?

Although there are exceptions with specific subtypes, most sarcomas can unfortunately come back, or recur, and so it is important to undergo surveillance with regular MRI or CT scans and follow-up with a sarcoma specialist. This continues for at least the first 2 to 3 years after completing treatment, sometimes to 5 years and, in some cases, extends indefinitely. Over time, if there continues to be no evidence of disease, the type of imaging study can transition to ultrasound of plain film X-rays (for example, chest). Importantly, the plan for surveillance should be individualized to each patient.

What else is important to know about sarcoma?

Because it is so rare, the treatment of sarcoma should be done at a specialized center with physicians who have experience and expertise in this specific disease. Research clearly demonstrates that patients have better outcomes when seen by sarcoma specialists. The treatment plan can be complicated, so the best approach is through a multidisciplinary team discussion that involves sarcoma experts from surgery, medical oncology and radiation oncology. Each patient case is presented at a “tumor board” with combined input from these experts.

Surgery for sarcoma is also best performed by a surgical oncologist (cancer surgeon) specifically trained to manage this frequently challenging disease. This avoids inappropriate treatment, such as incomplete or overly aggressive surgery. The sarcoma surgeon balances technical skill with intimate knowledge of the disease, personalized to each individual patient.

Keck Medicine of USC is the University of Southern California’s medical enterprise, one of only two university-owned academic medical centers in the Los Angeles area.