Pathology refers to the examination or study or the biopsy material or tumor by a specialized physician referred to as a pathologist. The pathologist studies the appearance of the tumor, both to the naked eye and under a microscope to determine the diagnosis. Special tests may also be performed. Sometimes the diagnosis is difficult especially for musculoskeletal tumors because they are rare tumors. The biopsy material should be examined by a pathologist who is experienced with bone and soft tissue tumors so that an accurate diagnosis is made. This is important since the treatment is based on the pathologic diagnosis. Sometimes 2nd and even 3rd opinions are required for an accurate diagnosis. The pathologist must decide if the tumor is benign or malignant (cancerous) and whether it is a sarcoma or carcinoma. If it is a sarcoma the pathologist must decide whether the sarcoma is low grade (less aggressive tumor) or high grade (very aggressive tumor).

The radiological studies are important for the pathologist to determine a diagnosis. The pathologist must make sure that his diagnosis matches the interpretation of the radiological studies (Xray, MRI, CT Scan). It is important for the pathologist to review the radiological reports and studies before making a final diagnosis. The pathologist must often review the scans with a musculoskeletal radiologist before determining the final diagnosis.

Sarcomas are graded by pathologists. When the pathologist views a biopsy specimen or the final tumor under the microscope, he assigns a grade to the tumor. The grade is based on particular characteristics of the cells that compose the tumor. The grade reflects the degree of malignancy of the sarcoma. The degree of malignancy reflects the potential for the tumor to come back locally (local recurrence) and spread to other parts (metastasize). Sarcomas can be divided into low, intermediate, and high grade tumors. Low grade tumors grow slowly and have very little chance of spreading to other areas of the body. High grade tumors grow rapidly and have a high likelihood of spreading to other body parts, particularly the lungs. Usually, high grade sarcomas have already spread microscopically to other parts of the body by the time the tumor is noticed by the patient. The behavior of intermediate grade tumors falls somewhere in between low and high grade tumors. The grade of the tumor helps determine the type of treatment. Higher grade tumors are generally treated with more aggressive surgery. High grade tumors respond to chemotherapy and low grade tumors do not respond to chemotherapy. High grade tumors tend to respond better to radiation in comparison to low grade tumors. Thus chemotherapy is usually only used for treating high grade tumors with rare exceptions.