Soft tissue sarcoma (STS) is a rare group of cancers originating in the body’s connective tissues, such as fat, muscle, nerves, blood vessels, and fibrous tissues. This malignancy can develop anywhere, but it is most commonly found in the limbs and trunk. Standard blood tests, like the routine Complete Blood Count (CBC), cannot definitively confirm or rule out STS. STS is a localized tumor that does not typically release specific, high-concentration protein markers into the bloodstream. Blood work is routinely performed for patients with suspected STS, but its purpose is to provide supportive information about overall health, not to serve as the primary diagnostic tool.
Definitive Diagnosis Through Imaging and Biopsy
The definitive diagnosis of soft tissue sarcoma relies on physical examination, advanced imaging, and tissue sampling. Since STS tumors are often deep within soft tissues, imaging studies are the first step to precisely locate and characterize the mass. Magnetic Resonance Imaging (MRI) is the preferred method because it provides detailed pictures of soft tissue structures, helping determine the tumor’s size and its relationship to nearby structures.
Computed Tomography (CT) scans are also used, particularly to check if the sarcoma has spread to distant organs, most commonly the lungs. However, imaging alone cannot confirm if a mass is benign or cancerous. The only way to definitively diagnose STS and determine its specific subtype and grade is through a biopsy.
A core needle biopsy is the most common technique, using a specialized needle guided by imaging (like ultrasound or CT) to remove small tissue cylinders. Pathologists examine this tissue under a microscope to confirm cancer cells and identify the specific type of sarcoma. The tissue sample is also used for genetic testing, which reveals chromosomal changes or fusion proteins characteristic of certain sarcoma subtypes.
Non-Specific Blood Markers and Supportive Lab Work
Blood tests cannot diagnose soft tissue sarcoma, but they are a standard component of the overall patient workup. These lab tests provide a picture of the patient’s general physiological state before treatment is initiated. A Complete Blood Count (CBC) is routinely ordered to check for anemia, which can be caused by chronic disease or internal bleeding if the tumor is large.
The CBC also monitors white blood cell and platelet counts, offering insights into the body’s immune response and clotting ability. A Comprehensive Metabolic Panel (CMP) assesses the function of major organs, such as the liver and kidneys. This assessment is important for staging the cancer, as dysfunction can suggest that the sarcoma has metastasized to these organs.
General inflammatory markers, like the Erythrocyte Sedimentation Rate (ESR) or C-Reactive Protein (CRP), may show elevated levels in a patient with STS. These elevations indicate a significant inflammatory process is occurring, but they are non-specific and can be raised by many conditions other than cancer. Supportive lab results are used by the oncology team to evaluate a patient’s fitness for surgery, chemotherapy, or radiation, not to confirm the sarcoma itself.
Using Blood Tests for Monitoring Treatment Response and Recurrence
After treatment for soft tissue sarcoma, specialized blood tests are increasingly used to track the disease and monitor for recurrence. This monitoring relies on the concept of a “liquid biopsy,” which analyzes Circulating Tumor DNA (ctDNA) shed into the bloodstream by cancer cells. CtDNA assays are highly sensitive and can detect microscopic traces of the tumor’s unique genetic material remaining after surgery or other therapies.
Personalized ctDNA tests are often utilized for monitoring. These tests first analyze the genetic mutations found in the patient’s original tumor tissue. This tumor-informed approach creates a unique molecular fingerprint used to track residual disease in subsequent blood samples. A decrease in ctDNA levels after treatment, such as chemotherapy or surgery, suggests the therapy has been effective in reducing the tumor burden.
The presence of detectable ctDNA following curative treatment can indicate Minimal Residual Disease (MRD), signaling a high likelihood of future relapse. Studies show that a rise in ctDNA levels can predict disease recurrence or progression months before it becomes visible on traditional imaging scans. This early warning system allows oncologists to potentially change treatment plans sooner, leading to a more personalized and proactive approach to surveillance.