Characteristics of Malignancy in Neoplasm
Embryonic Tumors of Infancy
(Tumors In Childhood) Some of these
tumors are present at birth, but most develop within the first 5 years of life.
Wilm's tumor (nephroblastoma)
This renal malignancy manifests as
an abdominal man in infancy and early childhood.
Neuroblastoma
The tumor arises from adrenal
medulla or one of the sympathetic ganglia. It appears as abdominal swelling in
childhood,
Medulloblastoma
This highly malignant brain tumor is
found in the region of the fourth ventricle near the cerebellum. It occurs
predominantly in young children.
Retinoblastoma This is the highly
malignant tumor of the retina found in infancy and early childhood.
Characteristics Of Malignant Neoplasms
Differentiation And Anaplasts
Lack of differentiation of tumor
cells is called) anaplasia. It is a characteristic of cancerous cells and it
constitutes one of the features that make a tumor as malignant The anaplastic
changes are characterized by
1) Pleomorphism (variation in size
and shape) Some cells may be many times larger and other smaller than their
neighbors
2) Hyperchromasia :
The nuclei contain an abundance of
DNA and are extremely dark staining
3) Disturbed nuclear -cytoplasmic
ratio:
Normal ratio is 1:6 but in anaplass
size of the nucleus becomes larger and ratio between nucleus and cytoplasm
becomes 1:1 Chromatin becomes clumped and is distributed along the nuclear
membrane.
4) Mitotic figures:
The numbers of mitotic figures
become large reflecting the proliferating activity of the parenchymal cells
Higher the number of mitosis , higher is the aggressiveness of a cancer. The
mitotic figures are atypical producing tripolar, quadripolar, or multipolar
spindles instead of bipolar.
5) Tamar giant cell:
Some giant cell contains only a
single huge nucleus while other have two or more nuclei.
6) Loss of orientation:
The normal orientation of one cell
to the other is lost, so that they grow in haphazard fashion. Normal
orientation of cells to their basement membrane is also lost (loss of
polarity).
Invasion
Mechanisms that make cancer invasive
are: Physical pressure.
Reduced adhesiveness of tumor cells.
Increased motility of tumor cells.
Loss of contact inhibition
Release of destructive enzymes
collagenase and plasminogen activator
All tissues of the body can be
invaded by cancer but some are vulnerable and other some resistant or elastic
fibers are more resistance than collagen fibers because malignant tumors
produce elastase in less quantity than collagenase.
Cartilage is the most resistant of
all tissues to invasion.
Arteries are much more resistant to
invasion than veins and lymphatics due to higher elastin content in arteries.
Spread
Malignant tumors spread by two ways:
Local spread or Infiltration By this
way malignant cells infiltrate the surrounding tissues usually in the line of
least resistance, like tissue plans. During infiltration the malignant cells
may invade the lymphatics and blood vessels.
Metastasis
Metastasis is a process in which
malignant tumor cells invade vessels or tissue spaces in such a manner that
they detach, migrate and are translocated to a distant site, where they lodge
and grow in the new location to form a secondary tuner.
The malignant tumors which are
locally invasive but never metastasize are (1) Basal cell carcinoma of the skin
and (ii) Gliomas of brain.
Essential factors for metastasis
Release of viable tumor cells
Due to deficiency of calcium, the
cell loss adhesiveness and this result in the separation of cells from the main
mass. These cells may be carried to some other suitable tissue and there they
start growing as a new tumor
Presence of suitable environment:
Spleen and skeletal muscles are
rarely. affected by the metastasis.
Lung, liver, bone and adrenals are
most suitable for metastasis.
Availability of spreading pathway:
Metastatic pathways
Lymphatic pathway:
It is the most common pathway for
the initial dissemination of carcinomas, but sarcomas may also use this route.
Blood stream: This pathway is
typical for sarcomas, but carcinomas may also use this route. Arteries are less
readily penetrated than veins.
Seeding of body cavities and
surfaces: In this pathway malignant neoplasm penetrates into natural open field
eg peritoneal cavity, pleural, pericardial and joint spaces. Such seeding is
characteristics of ovarian carcinoma in which all pericardial and joint spaces.
Such seeding is characteristics of ovary carcinoma in which all peritoneal
surfaces become coated with heavy layer of cancerous cells.
Transplantation: This is a process
of mechanical transport of tumor fragments by instruments or gloved hands.
Grading and staging of cancer
Grading It is a method by which the
level of differentiation of cancer is determined. The cancers are died in
grade- to grade IV with increasing
Staging a method by which the extent
of spread of a cancer is determined. It is based on.
Size of primary lesion
Is extent of spread to regional
nodes
Presence or absence of metastasis.
TNMs
TNM system is used for staging the
cancer. It is characterized by:
T- for primary tumor
N for regional lymph node M for
metastasis
T1, T2, T3 and T4 describe
increasing size of the primary tumor.
N.NI N2. and NJ indicate
progressively advancing lymph node involvement MO and MI reflect absence or
presence of metastasis
Note: Grading is done on
pathological ground while staging is done on clinical ground
Changes In Cell Due to Malignancy
The changes in a cell when it
becomes malignant are the following
Changes in growth property
The cell escapes from regulatory
control, fails to become mature and acquires the capacity of transplantation
(can grow in artificial media).
Morphological changes Variation in
size and shape occurs
Karyotypical changes :Changes occur
in genes eg change in the
Philadelphia chromosome in chronic
myelogenous leucxkemia
Antigenic changes
The tumor cells best antigens that
are different from those of normal cells, which are recognized by the host
immune system that produces immune response to destroy the tumor. The tum
antigens may be of three types
Tumor specific antigens: They are
only present on tumor cells and not on any normal cells eg melanoma associated
antigen-1 6
Tumor associated antigen: They are
present on tumor cells and also on some normal cells eg prostate-specific
antigen
Oncofetal antigens: This group of
antigen consists of substances normally produced in quantity during fetal life
hat not to any great extent by adult cells Le, they are produced by tumors eg
carcinoembryonic antigen and alpha fetoprotein
Metabolic changes:
The more anaplastic and
undifferentiated the tumor cell, the greater the deviation from the enzyme
system of the normal cells.
Cell membrane changes
There is loss of adhesiveness to
other cells. Synthesis and release of growth factor
Impaired cell-to-cell communication.
Elaboration and release of
degradative enzymes
Tumor cell products
The synthesis and secretion of
various tumor cell products are important for two reasons. Their presence may
indicate the existence of a neoplasm in the body ie . they act as tumor
markers.
They may produce clinical effects
called paraneoplastic syndromes:
Tumor Markers
Oncofetal antigen
These are antigens that are normally
expressed only in fetal life, but may be produced by neoplastic cells, eg
Carcinoembryonic antigen (normally
present in embryonic and fetal endodermal tissue) is found in most malignant
neoplasms arising from tissues that develop from embryonic endoderm such as
colon and pancreatic cancers
Alpha Fetoprotein They are
synthesized by normal yolk sac and fetal liver-and then by carcinoma of liver
and yolk sac carcinoma of gonads.
- Example is increased serum acid phosphatase in carcinoma of prostate.
- Raised in multiple myeloma.
- Excessive hormone production
- In neoplasm of endocrine cells. Ectopic hormone production.
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