As with most other malignancies, soft tissue sarcomas are assigned a histological grade. The French Federation of Cancer Centers Sarcoma Group (FNCLCC) is the most commonly used methodology and is preferred by the American Joint Committee on Cancer (AJCC) [1]. This system assesses tumor differentiation, mitosis, and necrosis and assigns a score for each characteristic (Table 3.1) [2, 3].

The differentiation score generally reflects how closely the tumor resembles benign mesenchymal tissue. For example, a well-differentiated liposarcoma (which closely mimics adipose tissue) would receive a low score (of 1), and a dedifferentiated liposarcoma (which has lost its lipogenic differentiation) would receive a high score (of 3).

A mitotic score is assigned according to the number of mitosis identified after viewing ten standard high-power fields through the microscope. One point is assigned for 0–9 mitosis, two points are assigned for 10–19 mitosis, and three points are assigned for 20 or more mitosis over ten high-power fields.

A necrosis score is rendered according to the amount of tumor necrosis present. Two points are assigned for more than 50% necrosis. One point is assigned for less than 50% necrosis, and no points are assigned if there is no necrosis.

These scores are then summated, and a numeric grade (1–3) is assigned accordingly (Table 3.2). This approach successfully categorizes a diverse group of malignant soft tissue sarcomas in a manner that independently predicts metastasis, but it is not used for all sarcomas. Some tumors that are classified as “malignant,” such as epithelioid sarcoma, clear cell sarcoma, and alveolar soft part sarcoma, carry less risk for early (less than 5 years) metastasis and greater risk for late metastasis (greater than 5 years). Consequently, these tumors are not given an FNCLCC grade. Other tumors, like alveolar or embryonal rhabdomyosarcoma , have their own risk stratification system (such as the Intergroup Rhabdomyosarcoma Study Postsurgical Clinical Grouping System) and are not assigned a FNCLCC grade [4].

Grading can be challenging on needle core biopsies, primarily due to issues with sampling. Biopsies that fail to capture increased mitosis or tumor necrosis can result in assignment of an inaccurate lower grade [2]. Thus, it is important to consider a reported grade in light of the radiologic findings when determining whether or not the biopsy is representative.