Neoplasia 1

Neoplasia

Definition
The neoplasm (tumor) is an abnormal mass of tissue; the growth of which is virtually autonomous and exceeds that of normal tissue and persists after cessation of stimuli that initiate the growth (unlike non-neoplastic proliferation e.g. hyperplasia, regeneration and repair).
Neoplasms are generally classified into 2 types: benign and malignant.

Nomenclature
2 basic components: The transformed neoplastic cells and non transformed elements such as connective tissue.
The classification of neoplasms is based on their parenchyma.
Benign tumors:
In general; their names end with suffix "oma" e.g. benign mesenchymal tumors are named as tissue of origin + oma like leiomyoma, lipoma and chondroma; while benign epithelial tumors are named as architecture + oma like adenoma (tumor arising from glandular tissue) and papilloma (tumor producing finger like projections).

Malignant tumors:
Generally called cancers; their nomenclature is based on their appearance and presumed histologic origin.
They are broadly divided into 2 categories:
1. Carcinoma: It arises from epithelial cells e.g. squamous cell carcinoma and adenocarcinoma.
2. Sarcoma: It arises from mesenchymal tissue e.g. osteosarcoma and leiomyosarcoma.
** Teratoma (tumor of germ cells) have more than one parenchymal cell type (ectoderm-skin, mesoderm-bone and endoderm-gut epithelium).

** Mixed tumors develop when stem cells undergo divergent differentiation creating mixed tumors i.e. more than one parenchymal cells like pleomorphic adenoma of salivary glands and fibroadenoma of breast.

** Exceptions:
• Lymphomas: tumor of lymphoid tissue, all malignant.
• Melanoma: malignant tumor of melanocytes.
• Seminoma dysgerminoma: tumor of primitive germ cells
• Glioma: Majority are malignant.
• Nephroblastoma, retinoblastoma medulloblastoma: tumors of primitive embryonic cells, all malignant.

** Choristoma: they are non-neoplastic ectopic nodular nest of tissue e.g. ectopic pancreatic tissue in gastric wall.

** Hamartomas: They are malformations that present as a mass of disorganized tissue indigenous to the particular site e.g. melanocytic nevi, most hemangiomas and lung hamartoma (mixture of bronchi, cartilage, vessel and connective tissue forming a mass).






Characteristics of benign and malignant tumors.
Criteria Benign tumor Malignant tumor
Mode of growth - Expansion.
- Remain localized. - Infiltrate locally.
- Distant metastasis.
Rate of growth Slower. Faster.
Histological - Similar to tissue of origin.
- Cells are uniform in shape and size.
- Nuclei are normal. - Different from tissue of origin.
- Cellular pleomorphism in shape + size.
-Large pleomorphic nuclei, hyperchromasia, prominent nucleoli and increased mitotic activity.
Clinical features - Local pressure effect.
- Hormone secretion.
-Cured by adequate excision. -Local pressure and tissue destructive effects.
- Hormone secretion.
- Paraneoplastic syndrome.
- Not cured by excision.


Differentiation & anaplasia:
Differentiation it is the extent to which tumor cells resemble comparable cells of tissue of origin.
In most benign tumors; the cells closely resemble corresponding normal cells, while malignant tumors display a range of differentiation that form the basis of tumor grading.
Anaplasia is a lack of differentiation which is the hallmark of malignant cells.

Histopathological features of anaplasia:
1. Nuclear and cellular pleomorphism: Variation in size & shape of nuclei and cells.
2. Hyperchromatism: Darkly stained nuclei due to abnormal chromatin content ( a reflection of aneuplody).
3. Increased nucleo-cytoplasmic ratio reaching about 1:1 instead of normal 1:4-6.
4. Abnormal mitosis: This reflects increased proliferative activity & abnormal mitosis e.g. tripolar spindles.
5. Tumor giant cells: They contain single giant polypoid nucleus or multiple nuclei.
6. Prominent nucleoli & cytoplasmic basophilia reflecting active protein synthesis.
7. Loss of orientation of tissue architecture.

Rate of growth
Most malignant tumors grow faster than benign tumors; however, some malignancies grow slowly for years then enter the phase of rapid growth.
Some cancers are hormone sensitive so affected by variation in hormonal levels as in pregnancy and menopause e.g. CA breast and endometrial CA( estrogen dependent) and prostatic CA (androgen dependent).
Rapidly growing tumors develop central areas of ischemic necrosis because they outgrow their blood supply.