Characteristics of Benign and Malignant Tumors

Differentiation

Definition

The extent to which tumor cells resemble the cell of origin.

Resemblance to parent cells or cells of origin

There are three degrees of differentiation:

1. Well differentiated –completely resemble
2. Moderately differentiated –some resemblance
3. Poorly differentiated/undifferentiated

Anaplasia

Lack of differentiation.

Considered as hallmark of malignant tumors. Different morphological changes are seen in anaplasia:

a.      Pleomorphism

Change in size and shape of cell or nucleus. E.g. smooth muscle spindle tumor.

b.      Mitosis (abnormal)

Tumors may have large number of mitosis but these may be seen in benign tumors or even hyperplasia.

Presence of abnormal, bizzare mitosis is the feature of malignancy.

c.       Abnormal nuclear morphology

• Pleomorphic nuclei.
• Abundant DNA –become hyperchromatic (chromatin condenseàbasophilic stain)
• Coarse clumped chromatin,
• Distributed along nuclear membrane
• Nucleoli become prominent
• Change in nucleus to cytoplasmic ratio i.e. 1:1 (normal 1:4 or 1:6)

d.      Loss of polarity

It is disturbed orientation of anaplastic cells.

Sheets and large masses of tumor cells grow in disorganized fashion.

e.       Tumor giant cells (not constant feature)

Presence of large tumor cells in some malignant neoplasms.

Giant cell may possess a single huge nucleus or multiple nuclei.

Ischemic Necrosis

Growing tumor cells require blood supply. In many tumors, vascular stroma is less, so the centre of tumor area undergoes necrosis.

Architecture of cell is retained.

Dysplasia –seen in epithelial type of tumors

Disordered growth.

Definition

Loss in uniformity of individual cells as well as a loss in architecture orientation.

Cellular changes

Dysplastic cells possess:

1.  some degree of pleomorphism
2. Hyperchromatic nuclei
3. Abnormal mitosis

Dysplasia does not necessarily progress to cancer.

Degrees of dysplasia

Normal glandular epithelium (mucin secreting gland)

Mild moderate dysplasia

Seen in few layers of epithelium

Severe dysplasia (carcinoma in situ)

When all dysplastic changes seen in whole epithelial thickness but remain confined above the basement membrane. Basement membrane is intact.

Growth rate of tumors

Most malignant tumors grow more rapidly than do the benign tumors.

Aggressive tumors containing large pool of dividing cells respond quickly to chemotherapy as most anti-cancer agents act on cells that are in cycle.

Slow growing tumors have a peripheral compressed form, thus a capsule is present in benign tumors

Malignant tumors are rapidly growing, they infiltrate masses thus there is no chance of capsule formation

Local invasion

Normally all benign tumors grow as cohesive masses and remain localized.

They grow and expand and develop a rim of compressed connective tissue known as capsule.

Growth of cancer is rapid with infiltration and damage to surrounding structure.

Carcinoma in situ remains localized.

Metastasis

Metastasis involves tumor implants discontinuous with primary tumor.

Benign tumors do not spread.

With few exceptions, all cancers have property of metastasis:

1. Gliomas in CNS
2. Basal cell carcinoma in skin

Pathway of spread

1. Seeding of body cavities
2. Lymphatic spread
3. Hematogenous spread

Nomenclature

Nomenclature includes cell of origin + suffix

Suffix for benign tumors is “oma”.

While that for malignant is divided into:

• For epithelial origin “carcinoma”
• For mesenchymal origin “sarcoma”

Fibroma	Fibrosarcoma
Osteoma	Osteosarcoma
Adenoma	Adenocarcinoma
Chondroma	chondrosarcoma

Exceptions include:

1. Leukemia
2. Lymphoma
3. Glioma

Comparison of Benign and Malignant Tumors

	Benign	Malignant
Differentiation	Well-differentiated	Poorly differentiated
Anaplasia	Not a feature	Feature
Pleomorphism	Cells are normal	Pleomorphism present
Hyperchromatic cells	Absent	Present
Nuclear chromatin	Normal distribution	Coarse, arranged along nuclear membrane
Nucleus cytoplasm ratio	1:6	1:1
Nuclear shape	Normal	Variable
Mitotic number	Normal	Greater
Abnormal mitosis	Absent	Tripolar, tetrapolar or even multipolar mitotic figures seen
Loss of polarity	Absent	Present
Dysplasia	Absent	Present
Tumor giant cells	Absent	Present
Ischemic necrosis	Absent	May be present
Nomenclature	“oma”	“osteoma” or “sarcoma”
Rate of growth	Slow	Aggressive
Local invasion	Absent	Present
Metastasis	Absent	Present
Capsule	Present	Absent
Effect on host	Slight harm	Significant harm
Grading and staging	Not required	Done for treatment option selection
Treatment	Surgical removal is sufficient	Aggressive treatment with chemotherapy/radiotherapy or surgery