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bone tumors form when a bone cell
divides uncontrollably in forms a mass
or tumour if the tumor remains confined
and doesn't spread into surrounding
tissues then it's considered benign but
if the tumor invades into surrounding
tissues and metastasizes or spreads
through blood or lymph then it's
considered malignant malignant tumors
can either be primary which is when they
arise from bone cells or secondary which
is when a tumor develops somewhere else
in the body metastasized and spread to
the bones the most common sources of
tumor cells that affect the bones but
start somewhere else in the body are the
breast prostate the lungs the thyroid in
the kidneys
now even though bones vary in size and
shape they're all made of the same types
of cells in chief among them are
osteoblasts which build up new bone and
osteoclasts which help with bone
breakdown or resorption now in addition
to these there are some more primitive
cells in the bone marrow called human
mesenchymal stem cells and
neuroectodermal cells which have the
ability to differentiate into many cell
types including nerve fat bone and
cartilage cells
now in terms of anatomy looking at a
long bone like the femur it has two
epiphysis which are the ends that
contribute to joints with other bones
between the two epiphysis
is the diaphysis also called the bone
shaft in children and adolescents there
is an additional narrow portion between
the epiphysis in the diaphysis called
the metaphysis the metathesis contains
the growth plate the part of the bone
that grows during childhood in adults
the growth plate has ossified infused
with the diaphysis and the epiphysis
now there are genes that promote normal
cell growth called proto-oncogenes
with mutations proto-oncogenes become
oncogenes and these over stimulate the
cell growth to balance out cell growth
there are other genes called tumor
suppressor genes which promote apoptosis
or cell death of mutated cells so
oncogenes or mutated tumor suppressor
genes allow cells to keep growing
uncontrollably resulting in tumors all
right
primary bone tumors can be divided up
into ones that are most often benign and
those that are most often malignant
let's start with the most common benign
tumor which is an osteochondral and
commonly affects males under 25 years of
age osteochondroma is thought to arise
from mutations in the excess dose in one
or ext one in excess dose and two or
ext2 genes which encode the excess dose
and one in two proteins these proteins
help to synthesize heparin sulfate which
is a protein that regulates the growth
of the growth plate so in osteochondroma
a tumor arises from the growth plate and
it typically results in a lateral bony
projection this bony stalk is called an
excess ptosis and it has a cap made
mostly of heileen cartilage now
osteochondromas typically develop in the
metathesis of long bones most commonly
the distal femur in the proximal tibia
around the knee joint but they can also
occur in flat bones like the ilium one
of the hip bones as well as the scapula
another benign tumor is the giant cell
tumor of the bone quite a name a risk
factor for giant cell tumors is having a
bony trauma like a fracture or radiation
exposure the tumor cells arise from
osteoclast cells but then develop into
cells that have numerous nuclei
typically over 50 nuclei so you can
think of them as destructive little
giants the giant cell tumor typically
arises in the epiphysis of the long
bones like the distal femur in proximal
tibia on rare occasions this tumor can
become malignant especially in elderly
individuals
other benign tumors are osteoblast Oma's
and osteoid osteoma x' both of which
arise from osteoblasts both of these
tumors classically form an itis which is
a disorganized mix of small blood
vessels tiny rods of bone culture Bekele
a nun mineralized bony tissue called
osteoid in osteoid blessed ouma's the
nine died which is plural for nidus are
large with a diameter of over 1.5
centimeters in osteoid osteoma x' the
night i are smaller than 1.5 centimeters
in diameter and are often surrounded by
a ring of sclerotic bone tissue that
ring of sclerotic tissue often produces
prostaglandins which are small molecules
that trigger the sensation of pain Ostia
West Ouma's also tend to affect the
bones of the axial skeleton usually the
mandible and erode the surrounding bone
in comparison osteoid osteoma typically
affect the diaphysis of long bones like
the tibia and don't usually erode the
surrounding bone
now among the lignin tumors the most
common one is osteosarcoma osteosarcoma
z' arise from osteoblasts of different
sizes called pleomorphic and these cells
produce too much osteoid tissue
osteosarcoma is often form in the
metathesis where there's a lot of cell
division occurring they most commonly
affect adolescents some known mutations
that are linked to osteosarcoma include
mutations of the PRV protein also seen
in familial retinoblastoma a childhood
malignant tumor of the eye in the p53
protein which is also seen in
li-fraumeni syndrome a condition where
there are a variety of cancers
throughout the body
another type of malignant bone tumor is
Ewing sarcoma which is also common in
adolescence typically between the age of
10 to 20 years Ewing sarcoma is thought
to arise from neuroectodermal cells
which look like small round blue cells
on microscopy Ewing sarcoma is
associated with chromosomal mutations
specifically a translocation between the
EWS are one gene on chromosome 22 in the
fli one gene on chromosome 11 you can
remember this by 22 plus 11 equals 33
the jersey number of the former
basketball player
Patrick Ewing the EWS are one fli one
fusion results in the expression of an
abnormal protein called you guessed at
the EWS are one FLI one fusion protein
or more simply the Ewing sarcoma protein
this protein causes defects in the
differentiation process of human
mesenchymal stem cell in neuroectodermal
cells resulting in Ewing sarcoma tumor
cells Ewing sarcoma can affect a number
of different bones but most commonly
affects the femur in the sacrum
finally there are chondrosarcoma x'
which tend to affect the elderly
chondrosarcoma arises from the
chondrocytes which are cartilage
producing cells contra sarcoma mainly
affects bones of the pelvis but can also
affect long bones like the proximal
femur and proximal humerus on imaging
the mass is typically within the
medullary cavity
bone tumors commonly cause bone pain
swelling and fractures some unique
symptoms are that the pain of osteoid
osteoma typically gets worse at night
while osteochondromas and osteoblasts
Oma's sometimes press against spinal
nerves causing numbness and limb
weakness they can also cause avascular
necrosis of certain regions within the
bone if the tumor impinges on a major
blood vessel malignant tumors typically
cause a chronic inflammatory response
which leads to fever night sweats and
weight loss bony tumors often
metastasize to the lungs so in that
setting they can cause pulmonary
symptoms like coughing and shortness of
breath
the diagnosis of bone tumors starts with
medical imaging like x-rays CT scans and
MRI imaging or testing for serum tumor
markers that are specific for each type
of tumor some tumors also have some
classic x-ray findings for example
osteochondroma causes excess doses while
the giant cell tumor forms multi cystic
bone lesions that look like soap bubbles
osteosarcoma form lytic bone lesions
referred to as a sunburst appearance
because the radiating tumor streaks look
like sun rays osteosarcoma is also
caused the periosteum to lift and that's
commonly called cogman stri angle in
Ewing sarcoma x-ray shows lytic bone
lesions referred to as an onion skin
appearance because the periosteum looks
like a sliced onion bulb in
chondrosarcoma there are patchy lytic
lesions that make the bone look like a
moth-eaten piece of cloth
the treatment of bone tumors depends on
whether they are malignant or benign
benign tumors can be surgically removed
to reduce pain and the risk of fractures
while malignant tumors are treated with
radiotherapy chemotherapy in surgery
depending on the type and the spread of
the tumor all right as a quick recap
benign tumors include osteochondroma
which presents with excess ptosis giant
cell tumor which has giant cells and
looks like soap bubbles on x-ray osteoid
osteoma characterized by an itis less
than 1.5 centimeters in osteoblasts toma
whose 9 s is greater than 1.5
centimeters
the primary malignant tumors include
osteosarcoma that are made of large
pleomorphic cells and have a sunburst
appearance on x-ray Ewing sarcoma that
has round blue cells in a sliced onion
appearance on x-ray and chondrosarcoma
which has large multinucleated
chondrocytes in a moth-eaten appearance
on x-ray there are no known causes of
the bone tumors but among risk factors
we have rapid bone growth bone trauma
exposure to radiation z' and positive
family history of bone tumors
osteosarcoma is linked to our be one in
tp53 gene mutations while Ewing sarcoma
is thought to arise when there are EWS R
1 and FLI 1 gene mutations benign tumors
can be surgically removed if they're
causing symptoms while the treatment for
malignant tumors requires radiotherapy
chemotherapy and surgery
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