Classification of tumors

Any tissue taken from the patient's body that is suspected of a tumor process should be delivered to an institute or department of pathology (pathological anatomy) and properly evaluated there by an experienced pathologist.

The task of the pathologist is to morphologically (possibly cytologically, immunohistochemically or molecularly-genetically) examine the given tissue and determine the typing, grading and staging of the tumor.

Typing

Typing is the microscopic determination of the type of tumor.

• In terms of biological behavior, tumors can be divided into two main groups. They are:

1. benign tumors ;
2. malignant tumors .

This is a nomenclature division, often unrelated to prognosis (some malignant tumors can be fully cured; on the other hand, some benign tumors can threaten the patient's life).

• From the histogenetic point of view, we distinguish:

1. Mesenchymal tumors (originating from the connective tissue; generally referred to as sarcomas ; e.g. fibrosarcoma, hemangiosarcoma).
2. Epithelial tumors (originating from the epithelium; generally referred to as carcinomas ; e.g. basal cell carcinoma, squamous cell carcinoma, adenocarcinoma).
3. Neuroectoderm tumors (arising from neuroectoderm cells; e.g. malignant melanoma).
4. Germinal tumors (originating from germ cells; mainly affect the gonads, but can also occur extragonadally, e.g. in the mediastinum ; e.g. seminoma, yolk-sac tumor, embryonal carcinoma, teratoma ).
5. Choriocarcinoma (arises from the trophoblast, is often part of mixed tumors).
6. Mesothelioma (arises from the mesothelium; affects the pleura, pericardium, peritoneum and tunica vaginalis testis).

According to the WHO classification, the pathologist assigns an eight-digit numerical code to each tumor, which is divided by the number 1-3 (1 indicates a benign tumor, 2 a borderline tumor, 3 a malignant tumor).

The full code could look like this, for example: 4357-8907/1.

Grading

Grading is a microscopic determination of the degree of differentiation (maturity) of the tumor. It is denoted by the letter G. This is an important prognostic and predictive data. Usually, the less differentiated a tumor is, the more aggressive it is, but at the same time more sensitive to treatment.

1. G _x (degree of differentiation cannot be determined)
2. G ₁ (well differentiated tumor)
3. G ₂ (moderately differentiated tumor)
4. G ₃ (poorly differentiated tumor)
5. G ₄ (undifferentiated tumor)

Staging

Staging is determination of the extent of the tumor. A number of systems are used for staging. The most common is the TNM system.

	TNM
pTNM	postoperative, pathological classification
yTNM	posttherapeutic classification
rTNM	recurrence classification

• T (tumor; indicates tumor size)

1. T_x (size cannot be determined)
2. T₀ (none)
3. T₁
4. T₂
5. T₃
6. T₄ (growing into surrounding tissues - skin etc.)
7. T_is (carcinoma in situ)

• N (nodes; tells us if regional lymph nodes) are affected

1. N_x (cannot be determined)
2. N₀ (regional lymph node are not affected)
3. N₁
4. N₂
5. N₃

• M (Metastases; tells, if distant metastases have been established)

1. M_x (cannot be determined)
2. M₀ (no metastases presented )
3. M₁ (metastases present)

In the final analysis 5 stages with different prognosis are created:

• St.0 – carcinoma in situ; without metastases
• St.1 – small, invasive carcinoma; without metastases
• St.2 – larger invasive carcinoma; there may be minor lymph node involvement
• St.3 – extensive invasive carcinoma; extensive lymph node involvement
• St.4 – distant metastases in any extent of primary tumour

from other staging systems should be mentioned:

• Dukes system (I–III): is used for staging colorectal cancer .
• FIGO system (International Federation of Gynecology and Obstetrics) (I–IV): is used for staging malignant cervical cancer.
• Clark and Breslow classification: is used for staging Malignant melanoma.

Rating

The rating is a summary designation for determining the expression of important proteins and receptors in tumor cells. For example, the following markers are determined immunohistochemically:

• markers of proliferation and its regulation: Ki-67, p53
• hormone receptors: estrogen and progesterone receptors (breast cancer), androgen receptors (prostate cancer)
• receptors important for therapy: HER-2/neu ( breast cancer )

Links

References

• BENEŠ, Jiří. Studijní materiály [online]. ©2007. [cit. 2010-03]. <http://jirben2.chytrak.cz/materialy/onko_JB.doc>.

• PETRUŽELKA, Luboš – KONOPÁSEK, Bohuslav. Klinická onkologie. 1. edition. Praha : Karolinum, 2003. ISBN 80-246-0395-0.