Sarcoma accounts for roughly 1% of all adult cancers, making it one of the rarest cancer categories. In 2025, an estimated 13,520 new cases of soft tissue sarcoma will be diagnosed in the United States, compared to nearly 300,000 new breast cancer cases in the same year. That extreme gap in numbers is what defines sarcoma as a rare cancer and creates unique challenges for the people diagnosed with it.
Sarcoma by the Numbers
Soft tissue sarcomas develop in muscles, fat, blood vessels, nerves, tendons, and the lining of joints. Bone sarcomas (like osteosarcoma and Ewing sarcoma) are even less common. Together, these cancers represent a small fraction of all diagnoses, but they carry significant weight: an estimated 5,410 Americans will die from soft tissue sarcoma in 2025.
While sarcoma is rare in adults, it plays a much larger role in childhood cancers, making up about 15% of all pediatric cases. Osteosarcoma and Ewing sarcoma are the most common bone cancers in children and young adults, though even in this age group the overall incidence is low, roughly 6 to 11 cases per million depending on age.
Why Rarity Creates Real Problems
One major consequence of sarcoma’s rarity is misdiagnosis. Because most doctors encounter these tumors infrequently, symptoms are often attributed to something else first. In one study of sarcoma patients, about a quarter of those with soft tissue sarcoma and a third of those with bone sarcoma were initially misdiagnosed. Symptoms were commonly chalked up to lifestyle factors like a sports injury or a pulled muscle. The median time from first noticing a symptom to receiving a correct sarcoma diagnosis was nearly five months for soft tissue sarcomas and about four and a half months for bone sarcomas.
That delay matters. Sarcoma outcomes depend heavily on how far the cancer has spread at the time of diagnosis. When the tumor is still localized, the five-year survival rate is 83%. Once it has spread to nearby tissues or lymph nodes, that drops to 60%. For distant-stage disease, where the cancer has reached other organs, the five-year survival rate falls to 17%.
More Than 70 Different Subtypes
Sarcoma isn’t a single disease. The World Health Organization recognizes approximately 70 distinct subtypes of soft tissue sarcoma alone, each with its own behavior, appearance under a microscope, and treatment approach. The three most commonly diagnosed forms in adults are gastrointestinal stromal tumors (GISTs), which start in the digestive tract; liposarcomas, which develop in fatty tissue; and leiomyosarcomas, which arise from smooth muscle. But many subtypes are extraordinarily rare even within this already rare cancer family, sometimes affecting only a few hundred people per year in the entire country.
This diversity is part of what makes sarcoma so challenging to treat. A treatment that works well for one subtype may be ineffective for another. Getting an accurate subtype diagnosis, ideally at a cancer center with sarcoma expertise, can meaningfully affect the treatment plan and outcome.
Who Gets Sarcoma
Most sarcomas have no clearly identified cause. They can develop at any age and in nearly any part of the body. However, a small number of genetic conditions substantially raise the risk. The most well-known is Li-Fraumeni syndrome, caused by inherited mutations in a key tumor-suppressing gene. People with this syndrome face a cumulative cancer risk of roughly 50% by age 40 and up to 90% by age 60. Soft tissue sarcoma is one of the core cancers associated with the condition, with lifetime incidence rates of about 15% in women and 22% in men who carry the mutation.
Prior radiation therapy also increases sarcoma risk. A small percentage of sarcomas develop in areas of the body that were previously treated with radiation for another cancer, sometimes years or even decades later. Beyond these known risk factors, most cases appear to arise spontaneously without a clear genetic or environmental trigger.
What Sarcoma Typically Looks Like
Soft tissue sarcomas often present as a painless lump that grows over weeks or months. Because painless lumps are common and usually benign (lipomas, cysts), it’s easy to dismiss them. The general guidance is that any soft tissue mass larger than a golf ball, or one that is growing or deep within the muscle rather than just beneath the skin, warrants imaging and potentially a biopsy. Bone sarcomas more often cause persistent pain in the affected area, sometimes accompanied by swelling or a noticeable mass.
The rarity of sarcoma means that the vast majority of lumps and bumps are not cancerous. But that same rarity is exactly why awareness matters. Patients who push for further evaluation of a persistent or growing mass, and doctors who consider sarcoma in the differential, can shorten the diagnostic timeline that currently stretches to months for many patients.