Sarcoma

A sarcoma is a rare type of cancer that begins in mesenchymal cells. These are the cells that form connective tissues throughout the body. Because they originate in these specific cells, sarcomas grow in parts like bone, cartilage, muscle, fat, or vascular tissues.

While there are five main types of cancer classified by cell origin, sarcomas are much less common than carcinomas. In adults, sarcomas represent only about 1% of all cancer diagnoses. However, they are more frequent in children, making up 15% of childhood cancer cases. The name comes from the Greek word for a "fleshy excrescence."

Doctors usually divide sarcomas into two major groups. The first group is bone sarcomas, which grow in the skeletal system. The second group is soft-tissue sarcomas, which grow in the body's softer structures. Each group contains many different subtypes. For example, osteosarcoma is a type of bone sarcoma. Liposarcoma is a subtype of soft-tissue sarcoma that involves fat cells.

There are also primary and secondary tumors. A primary sarcoma starts in the connective tissue itself. A secondary or metastatic tumor occurs when cancer from another organ, like the lungs or breast, spreads to the connective tissue.

Many different subtypes exist within these two groups. The American Joint Committee on Cancer (AJCC) provides guidelines for classifying these subtypes. Bone sarcomas include varieties like chondrosarcoma, angiosarcoma, and chordoma. Soft-tissue sarcomas include many types, such as leiomyosarcoma, rhabdomyosarcoma, and synovial sarcoma. Some subtypes are even more specific. For instance, liposarcoma includes varieties like myxoid sarcoma and dedifferentiated liposarcoma. This complex classification helps doctors understand exactly which tissue is affected.

Scientists are still learning the exact molecular changes that cause these cancers. Sometimes, a chromosomal translocation occurs. This is when parts of two different chromosomes break and fuse together. In Ewing sarcoma, part of chromosome 11 fuses with part of chromosome 22. This creates an abnormal protein from the EWSR1 gene. In dermatofibrosarcoma protuberans, the COL1A1 gene fuses with the PDGFRB gene. This causes over-active signaling that promotes cell division. Other types, like liposarcoma, may involve an amplification of chromosome 12. This means the cells have extra copies of cancer-promoting genes called oncogenes.

Several risk factors are linked to the development of sarcomas. Some people are born with inherited genetic syndromes. Examples include Li-Fraumeni syndrome, neurofibromatosis type 1, and RB1 gene mutations. Exposure to certain environmental factors can also increase risk. Ionizing radiation, such as from previous radiation therapy, is a known factor. For soft-tissue sarcomas, exposure to chemicals like arsenic or vinyl chloride is linked to angiosarcoma. Additionally, the Kaposi sarcoma is caused by the Kaposi sarcoma-associated herpesvirus (HHV-8). These diverse causes explain why sarcomas appear in different ways in different people.

Diagnosing a sarcoma requires several careful steps. Doctors often start with a physical exam to check for symptoms. Bone sarcomas might cause pain at night or swelling. Soft-tissue sarcomas often appear as firm, painless lumps. Doctors use imaging tools like X-rays, MRI, or CT scans to see the tumor. They may also use a radioisotope bone scan to check for spread. However, a definitive diagnosis requires a biopsy. During a biopsy, a pathologist examines a tissue sample under a microscope. This is the only way to be certain of the specific subtype.

Once diagnosed, doctors must perform staging and grading. Staging determines how advanced the cancer is. It looks at tumor size and whether there is local invasion or metastasis. Metastasis is when the cancer spreads to lymph nodes or distant organs, like the lungs. Grading describes how aggressive the cells look under a microscope. Low-grade sarcomas are less aggressive, while high-grade sarcomas are more likely to spread. Staging and grading are vital because they help doctors choose the best treatments. For example, high-grade tumors often require a combination of surgery, chemotherapy, and radiation.

Understanding these details has led to significant medical progress. In the past, the long-term survival rate for children with localized osteosarcoma was only about 20%. Because doctors discovered that many sarcomas are sensitive to chemotherapy, those numbers have changed. Today, the survival rate for those patients has risen to between 60% and 70%. This progress shows how studying the specific mechanisms of cancer can save lives. By identifying the exact type and grade, medical teams can fight these rare diseases more effectively.