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Clinical Pathology in Action > Soft Tissue Tumours > Flashcards

Soft Tissue Tumours Flashcards

1
Q

What is somatic tissue of mesenchymal origin

A

Tissues derived from the embryonic mesoderm, a germ layer that gives rise to a variety of structures including connective tissue, muscle, bone, and blood

  • Adipose tissue
  • Skeletal muscle
  • Nerves
  • Vessels
  • Fibrous tissue
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2
Q

What are the WHO classification of soft tissue tumours

A
  • Adipocytic tumours
  • Fibroblastic and myofibroblastic tumours
  • Vascular tumours
  • Pericytic tumours
  • Smooth muscle tumours
  • Skeletal muscle tumours
  • Tumours of uncertain differentiation
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3
Q

Where do soft tissue sarcomas develop the most

A
  • Connective tissue of the trunk
  • Organs within trunk
  • Limbs
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4
Q

What are adipocytic tumours

A

Neoplasms that arise from adipose tissue, they can be benign or malignant. The benign types are farm more common and generally harmless

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5
Q

What are Benign Adipocytic Tumours

A

The main type of benign adipocytic tumour is lipoma but there are several subtypes:

  • Fibrolipoma: lipoma with fibrous component
  • Angiolipoma: lipoma with numerous small blood vessels
  • Spindle cell lipoma
  • Myolipoma: contains smooth muscle in addition to adipose tissue
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6
Q

What is Lipoma

A

Occurs in adults, typically in the subcutaneous tissue (arms, shoulders, back, neck)

It is slow-growing, soft and usually painless

Can also occur in deep soft tissues and even organs

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7
Q

What is the histology of the lipoma

A
  • Composed of mature adipocytes
  • Cells are uniform in size and shape, with clear cytoplasm and eccentrically placed nuclei
  • No mitoses, no atypia, and no necrosis

-Often encapsulated or well-circumscribed

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8
Q

How is benign lipoma diagnosed

A
  • Clinical exam + imaging
  • Histopathology for confirmation
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9
Q

What are the two types of Malignant adipocytic tumours

A

1) Atypical Lipomatous Tumour/Well-differentiated Liposarcoma

2) Dedifferentiated Liposarcoma

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10
Q

What is Atypical Lipomatous Tumor / Well-Differentiated Liposarcoma (ALT/WDL)

A
  • Most common type of liposarcoma occuring in adults aged 40-60
  • Common sites: deep soft tissues and retroperitoneum
  • It is locally aggressive but does not metastasise
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11
Q

What is the difference between Atypical Lipomatous Tumor and Well-Differentiated Liposarcoma (ALT/WDL)

A

ALT: if it is in surgically accessible sites like limbs

WDL: deep, hard-to-resect sites, due to increased recurrence risk

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12
Q

What is the histology of ALT/WDL

A
  • Composed of mature adipocytes with variation in size
  • Presence of hyperchromatic, atypical stromal cells
  • Fibrous septa containing atypical cells
  • Low mitotic activity
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13
Q

What are the diagnostics for ALT/WDL

A

Amplification of MDM2 and CDK4 on chromosome 12q13-15 — a diagnostic hallmark

These can be detected via FISH or immunohistochemistry

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14
Q

What is Dedifferentiated Liposarcoma

A
  • Arises when a well-differentiated liposarcoma transforms into a higher-grade tumour
  • More likely to occur in the retroperitoneum and has greater metastatic potential than ATL/WDL
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15
Q

What is the histology of DDL

A
  • Shows abrupt transition between well-differentiated (lipoma-like) and dedifferentiated (non-lipogenic, high-grade sarcoma)
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16
Q

What does the dedifferentiated component show

A
  • Undifferentiated pleomorphic sarcoma, or fibrosarcoma
  • High cellularity, nuclear atypia, mitotic figures, necrosis
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17
Q

What are the molecular amplifications present in DDL

A

CDK4 and MDM2 amplification

MDM2 positivity by immunohistochemistry supports diagnosis

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18
Q

What is myxoid Liposarcoma and what is it characterised by

A

Malignant tumor of adipose tissue characterised by:

  • A myxoid (mucoid/gelatinous) extracellular matrix
  • Branching capillaries
  • Immature fat cells (lipoblasts)

It lies between well-differentiated and high-grade sarcomas in terms of aggressiveness

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19
Q

What is the epidemiology of myxoid

A
  • Second most common type of liposarcoma after WDL/ALT
  • Typically affects ages between 30-50
  • Commonly found in deep soft tissues of lower extremities, especially the thigh
  • Grows slowly but has a higher risk of metastasis than WDL especially to unusual sites like soft tissue, bone or retroperitoneum
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20
Q

What is the histology of myxoid liposarcoma

A
  • Abundant myxoid stroma with branching vascular pattern
  • Primitive non-lipogenic mesenchymal cells
  • Lipoblasts in various stages of differentiation
  • Some tumours show round cell components called ‘high grade myxoid liposarcoma’ it tends to behave more aggressively
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21
Q

What are the genetic features of Myxoid Liposarcoma

A

Caused by a specific chromosomal translocation that leads to the fusion of FUS-DDIT3 (CHOP) genes which inhibits adipocyte differentiation

This is diagnostic and can be detected via FISH or RT-PCR

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22
Q

What are smooth muscle tumours

A

Originating from vessels and superficially pilar erector muscles

They are cutaneous: superficial, small, multiple, painful

Bland smooth muscle tumour without mitotic figures

They can be associated with immunosuppression and EBV infection

23
Q

What is Leiomyosarcoma

A

This is a malignant tumour of smooth muscle origin. It tends to be aggressive with potential for recurrence and metastasis

24
Q

What are the common primary sites

A

Arms and legs

Large blood vessels especially:
- inferior vena cava
- Saphenous
- Femoral vein/artery
- Pulmonary artery

25
How is Leiomyosarcoma
Judged by a combination: 1) Mitotic activity 2) Necrosis 3) Size 4) Tumour location
26
What is each site with criteria for malignancy
Soft tissue: 1-2 mitoses per 10 HPF Skin: >2 mitoses per 10 HPF Retroperitoneum: >5 mitoses per 10 HPF Vascular: 1-4 mitoses per 10 HPF
27
What are skeletal muscle tumours - Rhabdomyoma
This is a benign tumour that originates from mature skeletal muscle cells. It is the non-malignant counterpart to rhabdomyosarcoma
28
What are the three main histological types of rhabdomyomas
1) Fetal Type 2) Adult Type 3) Genital Type
29
What is the Fetal Type Rhabdomyoma
- Occurs in infants in children and is composed of immature skeletal muscle cells that resemble fetal muscle - Occurs in the head and neck - Important to distinguish from embryonal rhabdomyosarcoma, which is malignant
30
What is the Adult Type of Rhabdomyoma
- Composed of well-differentiated, mature skeletal muscle cells - Most commonly found in the head and neck region: - Oral cavity - Pharynx - Larynx
31
What is the Genital type of Rhabdomyoma
- Occurs in females more often - Typically found in the vulva or vagina - Composed of elongated muscle cells but still benign
32
What are the key histological features of Rhabdomyomas
Cells resemble mature skeletal muscle fibers, often showing cross-striations Low cellular atypia, very few mitoses May show signs of degeneration and regeneration, suggesting a possible reactive or reparative origin in some cases
33
What is Embryonal Rhabdomyosarcoma
- Most common sarcoma in the pediatric and adolescent setting - TP53 mutations that lead to the overexpression of p53 protein is associated with anaplasia - There is some degree of myogenic differentiation, including MyoD1 or Myogenin positivity - Displays some recurrent copy number changes
34
What is Embryonal Rhabdomyosarcoma, Botryoid Type
This is a type of cancer that comes from immature muscle cells (rhabdomyoblasts) Botryoid type: grape-like tumour growing underneath the mucosal epithelium
35
Where are the embryonal rhabdomyoblasts botryoid growths found
- Bladder - Vagina - Biliary Tract - Upper respiratory tract
36
What are the genetics of embryonal rhabdomyomas
- They are normally sporadic with no genetic predisposition - In children with predisposing familial syndromes, there are frequently defects in the RAS and Hedgehog pathways
37
What are the syndromes that predispose to soft tissue tumours
- Costello syndrome: Rhabdomyosarcoma - Neurofibromatosis Type 1: Neurofibromas, Malignant Peripheral Nerve Sheath Tumour - Noonan syndrome: Risk of Rhabdomyosarcoma - Li-Fraumeni syndrome: Soft tissue sarcomas
38
What is the alveolar rhabdomyosarcoma (ARMS)
Malignant soft tissue tumour that arises from skeletal muscle progenitor cells and it tends to be more aggressive than other types of rhabdomyosarcomas
39
Where does Alveolar Rhabdomyosarcomas happen
Thighs or arms Can also occur in the trunk, perineum, or head and neck region
40
What is the histology of ARMS
Tumor cells are arranged in clusters separated by fibrous septa, resembling the alveoli of the lungs In central areas of the clusters, the cells may fall away, creating empty spaces—this gives the "alveolar" appearance Cells are small, round, and undifferentiated with high mitotic activity
41
What is the genetics of ARMS
Two fusion proteins can be associated with alveolar rhabdomyosarcoma (ARMS): * PAX3-FOXO1 fusion gene * PAX7-FOXO1 fusion gene
42
What is the 1000 genome project
The 1000 Genomes Project aimed to describe and characterize the variations found in human genomes and served as a way of investigating the relationship between genetic polymorphisms and phenotypes by sequencing 2600 individuals from 26 populations from around the world.
43
What methods were used in the 1000 Genome Project to detect variants
Low coverage whole genome sequencing - sampled DNa more broadly as lower coverage had lower costs but was still useful for identifying common variants SNP arrays - scan specific known locations in the genome where variation often occurs Deep exome sequencing - focused, high-resolution sequencing of the exons
44
How did the 1000 Genome Project improve upon earlier studies
It was designed to capture both common and rare genetic variants, which earlier studies might have missed
45
What is the 100,000 genomes project
- Aims to describe and characterize the variations that are found in the human genome - This serves as a way of investigating the relationship between genetic polymorphisms and phenotypes by sequencing 2600 individuals from 26 populations around the world
46
What is whole genome sequencing
It is the most direct method of detecting mutations, such as single nucleotide polymorphisms and copy number variations For personalised medicine, whole genome sequencing will be an important tool to guide therapeutic intervention
47
What is GWS focused at identifying
1) Germline variation detection 2) Somatic variation 3) Whole genome re-sequencing 4) Copy number variation 5) Structural variant discovery
48
How is the reference genome built
1) Break the genome into large fragments and clone them - The genome is chopped into large pieces and inserted into cloning vectors like bacterial artificial chromosomes 2) Break individual clone into small fragments 3) These small fragments are sequenced, producing short sequence reads 4) The short reads are computationally aligned and overlapped to reconstruct the full genome - this results in a reference genome
49
How is individual's genome sequenced
1) Break the genome into small fragments 2) Generate millions of sequence reads 3) The sequence reads are aligned into a reference genome to detect: - Variations - Mutations - Structural changes
50
What is the purpose of assembling a reference genome
To create a standard genomic sequence that can be used as a baseline for comparing individual genomes
51
Why are individual genome reads aligned to a reference genome
To identify variations such as SNPs, insertions, deletions, structural mutations.
52
What is the point of WGS
- Been used as a research tool - May be an important tool to guide therapeutic intervention - The tool of gene sequencing at SNP level is also used to pinpoint functional variants from association studies and improve the knowledge available to researchers interested in evolutionary biology - This may lay the foundation for predicting disease susceptibility and drug response
53
What are the different uses of genomics in medicine
1) Pharmacogenomics - precision in dosing and avoidance of drug toxicity 2) Early detection of cancer - circulating tumour DNA in blood to detect recurrence early 3) Newborn screening and carrier testing - for severe inherited diseases 4) Identification of people with inherited high risk of cancer - To direct intensive screening, preventive drugs, and risk reducing surgery 5) Rare diseases - Attaining a specific genetic diagnosis to improve patient management.
54
How would WGS help in diagnosing sarcomas
- A better understanding of the genetic background of sarcomas would allow the development of more accurate/effective treatment options which could target specific triggering mutations, possibly shared by more than one tumour - Moreover, identification of germline mutations could promote testing of entire family groups identifying individual at risk of certain conditions

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