Grading is understood as the histological assessment of tumor cells according to their state of differentiation. Consisting of four levels, the evaluation follows the severity in which the abnormal cells differ from healthy tissue. Well differentiated tumors (low grade) generally have a better prognosis than poorly differentiated tumors (high grade).
|G1||Well differentiated, close similarity to original tissue (“low grade“)|
|G2||Fairly differentiated malignant tissue|
|G3||Poorly differentiated malignant tissue|
|G4||Undifferentiated malignant tissue; the original tissue which gave rise to the tumor can only be determined by immuno-histochemical evaluation or not at all|
|G9||Cannot gauge level of differentiation|
Aside from a few exceptions, grading is performed on all types of tumors: prostate tumors receive histologic assessment according to the GLEASON-Score while brain tumors have their own WHO classification.
Staging defines the stage of the tumor disease according to the extent to which it has spread throughout the body. Solid tumors are usually classified by using the TNM system. This system of classification has been administered by the UICC (Union Internationale Contre le Cancer) since the 50s and is regularly updated.
The three letters (T, N and M) stand for the separate categories: tumor (primary tumor), node (= involvement of lymph nodes) and status of metastases.
|Primary tumor (T)||Tx: Primary tumor cannot be assessed
T0: Absence of primary tumor
T1–4: Assignment of various stages occurs according to specific tumor, taking into account different criteria such as size (diameter), invasive depth, infiltration of neighboring tissue and organs
|Involvement of lymph nodes (N)||Nx: Involvement of lymph nodes cannot be assessed
N0: No involvement of lymph nodes
N1–3: Number and localization of involved lymph nodes
|Distant metastases (M)||Mx: Distant metastases cannot be assessed
M0: No metastases
M1: Distant metastases observed
An example of tumor description according to TNM classification could be T1N0M0. This would mean that the tumor has only moderate localized spread, does not affect any lymph nodes and there are no distant metastases.
Lower case letters which precede the TNM code help to provide additional information. For example, ”a” means that a tumor was discovered by means of an autopsy, ”c” advises of clinical diagnosis, ”p” specifies confirmation of stage through pathological evaluation, ”y” means previous neo-adjuvant therapy, and ”r” indicates reoccurrence.
The combination of all three categories finally determines the tumor stage. Criteria for staging is specifically defined according to tumor type and is based on the statistical analysis of stage-specific prognosis and corresponding treatment options.
Staging is a routine part of tumor diagnostics since it has considerable influence on the course of the treatment. Necessary examination includes, among others, radiological modalities such as ultrasound, CT and x-ray (determination of tumor size and local spread, lymph node involvement as well as distant metastases), nuclear medicine, and tissue sampling for histological, immuno-histochemical and/or cytological examination.