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• Neoplasia 1.1 & 1.2 - Pathology and genetic background of skin tumours

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• Which two type neoplasms are there?

  Benign and Malignant neoplasm

• Characteristics of benign neoplasm

  • Only local growth
    
  • no invasion in other tissue
  • no metastases
  • often slowly growing
  • cell without 'atypia'

• Characteristics of Malignant neoplasm

  • Invasion into other tissue
    
  • can metastasise
  • often rapid cellular growth, mitosis and meiosis
  • cell with 'atypia' 

• Types of genetic alterations leading to neoplasia:

  • Mutations
  • structural chromosomal alterations translocations
  • copy number variations: losses or gains of parts or whole chromosomes.
  • viral transformation (not discussed in detail)
    

• Mutation = a nucleotide change in DNAforms of mutations: 

  Substitution 
  
  Frameshift:
  insertion
  deletion

• 3 types of genes can be involved in oncogenesis:

  1. (proto)oncogenes
  

  • funcion: promotion of cell proliferation and survival
  • mutation/amplification: gain of function/ activation/ over expression

  
  2. tumor suppressor genes
  

  • Function: inhibition of cell proliferation of induction of apoptosis
  • Mutation/loss: inactivation/loss of function

  3. mutation / mismatch repair genes
  
  

  • Function: repair of DNA replication errors
  • Mutation: loss of function (accumulation of DNA errors)

• Two types of mutations are:

  Somatic
  

  • acquired
  • present only in certain cells of the body, dependent on cause
  • e.g. UV induced TP53 mutation in epithelial cells of the skin

  
  Germline mutations
  

  • Hereditary, congenital
  • present in all cells of the body

• What are some simple alterations of Benign neoplasia's?

  • Most common nevi (moles) have only one mutation. 60% BRAF, 20% NRAS
    
  • Spitz nevi (non pigmented moles in children) have one chromosomal translocation. ALK, ROS of NTRK translocation
  • Some spitz nevi have one HRAS mutation and one gain of chromosome 11p

• Cancer is a multistep process: clonal evolution model

  • Several mutations (usually at least 6 steps) in different genes controlling cell growth, different and death.
    
  • often starting with a precancerous genetic change
  • addition genetic changes lead to cancerous growth
  • autonomous cell proliferation
  • loss of cell contact inhibition: invasion occurs
  • new vessels develop
  • growth in to vessels and metastasis can occur

• What is the largest organ of the body?

  The skin. About 4 kg. That's why skin cancer rising, life long exposure to UV light.