A16. Classifications of malignant tumors. TNM-grading.

From greek.doctor

It’s important for physicians to be able to communicate information about tumors in a standard, unambiguous way. By creating criteria, we can more easily determine the clinical behaviour of the tumor. To do this, we created two description protocols for cancers: grading and staging.

Grading of a cancer describes its degree of differentiation, i.e. how similar the cancer cells are to the corresponding healthy types of cell. A cancer is said to be well-differentiated if it acts like healthy tissue would, e.g.:

  • It is epithelial in origin and produces keratin
  • It is glandular in origin and produces gland-like structures
  • Its cells show low degree of pleomorphism
  • Not a high number of mitotic figures can be seen

Well-differentiated tumors are less aggressive generally, so the more well-differentiated a tumor is, the lower its “grade”. A low-grade tumor is well-differentiated, a high-grade tumor is poorly differentiated or even anaplastic. We can divide tumors into 2, 3 or 4 “grades”:

Four-tier grading Three-tier grading Two-tier grading
Grade 1 Low grade Well-differentiated Grade 1 Low grade Well-differentiated Grade 1 Low grade Well-differentiated
Grade 2 Intermediate grade Moderately differentiated Grade 2 Intermediate grade Grade 2 High grade Poorly differentiated
Grade 3 High grade Poorly differentiated Grade 3 High grade Poorly differentiated
Grade 4 Anaplastic Anaplastic

Which system we use depends on the type of tumor.

TNM system

This figure shows how the T would vary in different types of colorectal cancer

Staging is another system that is has more clinical value than grading. The most common system is the TNM system, which describes the size or extent of the tumor (T), the involvement of lymph nodes (N) and whether there’s metastasis or not (M). The system works like this:

T N M
Tx Tumor can’t be evaluated Nx Lymph nodes can’t be evaluated M0 No distant metastasis
T0 No evidence of tumor N0 No tumor cells in sentinel lymph node M1 Metastasis to distant organs
Tis Carcinoma in situ N1 Tumor cells present in sentinel lymph node
T1 Size and extension of tumor on a scale from 1-4 N2 Between N1 and N3
T2 N3 Tumor cells has spread to distant or numerous regional lymph nodes
T3
T4

So a colorectal cancer which had spread to the submucosa, has spread to numerous lymph nodes and has no metastases would be T1 N3 M0.