Sarcoma is a rare form of cancer that originates in the body’s connective tissues, such as bone, muscle, fat, cartilage, blood vessels, and nerves. These tumors are distinct from the much more common carcinomas, which arise from epithelial tissues. Because sarcomas are uncommon and can present with vague symptoms, diagnosis involves a precise, multi-step process to identify the disease and classify its characteristics.
Recognizing Early Signs and Initial Assessment
The first indication of a potential sarcoma often involves a physical change noticed by the patient, prompting a medical visit. For soft tissue sarcomas, the most frequent symptom is a new or growing lump that is frequently painless. These masses are typically located deep within the limbs or trunk, and any lump that increases in size over several weeks or months should be evaluated.
Bone sarcomas, in contrast, commonly present with deep, persistent bone pain that may worsen at night or not improve with rest. This pain can sometimes lead to a pathological fracture—a bone fracture resulting from a minor injury. The initial medical assessment involves a thorough review of the patient’s history and a physical examination focused on the mass’s characteristics. The physician checks the lump’s size, location, and whether it feels firm or fixed to surrounding tissues. This evaluation determines if further, specialized testing is required to rule out a benign condition.
Visualizing the Mass Through Imaging
Once a suspicious mass is identified, imaging tests are performed to determine its nature and map its relationship to nearby structures. Imaging characterizes the mass, assessing whether it appears solid or fluid-filled, and determines its size and extent. These initial scans are performed before any tissue removal to ensure that a subsequent biopsy is planned correctly.
Plain X-rays are often the first images ordered, particularly when a bone sarcoma is suspected, as they show characteristic changes in bone density or structure. For most soft tissue lesions, Magnetic Resonance Imaging (MRI) is considered the definitive standard. MRI uses strong magnetic fields and radio waves to produce detailed cross-sectional pictures, allowing physicians to clearly see the tumor’s boundaries and its proximity to muscles, nerves, and blood vessels.
Computed Tomography (CT) scans offer detailed images of the body’s internal organs and soft tissues. CT scans are sometimes preferred for sarcomas located in the chest, abdomen, or retroperitoneum, where MRI can be less effective. A CT scan of the chest is routinely performed early in the process to check for potential spread to the lungs, a common site for sarcoma metastasis. Positron Emission Tomography (PET) scans, often combined with a CT (PET/CT), are utilized to assess the tumor’s metabolic activity and search for distant disease.
The Biopsy: Confirming Sarcoma
The only method to definitively confirm a diagnosis of sarcoma is by obtaining a tissue sample through a biopsy. The choice of biopsy method is a technical decision, as the path the needle or incision takes must be planned carefully to avoid contaminating surrounding healthy tissue. An improperly performed biopsy can complicate future surgical treatment, potentially requiring a more extensive operation.
The most common technique is the core needle biopsy, which is minimally invasive and involves inserting a hollow needle to extract several small cylinders of tissue. This procedure is often guided by imaging, such as CT or ultrasound, to ensure the tissue is taken from the most representative part of the tumor. If a core needle biopsy does not yield enough diagnostic material, or for tumors that are difficult to access, an incisional biopsy may be performed, which involves surgically removing a small piece of the tumor. An excisional biopsy, where the entire mass is removed, is generally avoided for suspicious sarcomas because it risks incomplete removal and disease spread.
The tissue samples are sent to a pathologist specializing in cancer diagnosis for microscopic analysis. The pathologist examines the cellular architecture to confirm malignancy and determine the specific sarcoma subtype; there are over 70 recognized types. This analysis involves looking at cellular differentiation, which describes how much the cancer cells resemble normal, healthy cells. The pathologist also calculates the mitotic rate, which counts how rapidly the cells are dividing. These microscopic details are necessary because the precise sarcoma subtype dictates the recommended treatment pathway.
Grading and Staging the Sarcoma
Following the definitive biopsy diagnosis, the tumor is subjected to a two-part classification process: grading and staging. Grading indicates the sarcoma’s aggressiveness and its potential to spread. This is based on the microscopic features identified by the pathologist, specifically the level of cellular differentiation and the mitotic rate.
Sarcomas are typically assigned a grade of 1, 2, or 3, corresponding to low, intermediate, or high grade. A low-grade tumor (G1) has cells that look relatively similar to normal cells and are expected to grow slowly. High-grade tumors (G3) are composed of highly abnormal cells that are dividing rapidly and are more likely to spread.
Staging determines the anatomical extent of the cancer within the body. The most widely used system is the American Joint Committee on Cancer (AJCC) TNM system, which considers four factors: the size of the primary Tumor (T), spread to nearby lymph Nodes (N), the presence of distant Metastasis (M), and the tumor Grade (G). The combination of these factors results in an overall stage, usually designated by Roman numerals I through IV. Stage IV is assigned if the cancer has spread to distant organs, most often the lungs, regardless of the tumor’s size or grade. Staging often requires additional imaging, such as a CT scan of the chest or a PET scan, to ensure no distant spread has been overlooked.