Melanoma

Question 1

What is the survival rate for melanoma after diagnosis?

Answer 1

90% will live for 10 or more years.

Question 2

What is the female:male ratio of melanoma?

Answer 2

Female:Male, 2:1 BUT mortality is higher in men. This may be due to behavioural characteristics.

Question 3

What subtypes of melanoma are there?

Answer 3

Cutaneous

Superficial spreading melanoma

Modular melanoma

Aural melanoma Uveal melanoma

Question 4

From which cells does melanoma arise?

Answer 4

Melanocytes - Predominant in the skin and eye tissue

Question 5

What is the most common form of melanoma?

Answer 5

Cutaneous melanoma - Arises from epidermal melanocytes on the skin

Question 6

Why are brain metastases hard to treat?

Answer 6

The blood brain barrier makes treatment by chemotherapy difficult. Brain tumours can impinge on vital organs and tissues of the body which can be fatal.

Question 7

What factors contribute to risk of melanoma?

Answer 7

Family history of melanoma

Multiple large moles and atypical moles

Sun exposure

Race and skin type

Xeroderma Pigmentosum - rare AR condition, mutation of genes involved in nucleotide excision repair

Question 8

What is MITF?

Answer 8

Melanocyte specific transcription factor

Activated pigmentation genes and cell survival genes Important player- can often be mutated in melanoma

Question 9

Where are melanocytes located?

Answer 9

At the bottom of the epidermis.

Question 10

How do melanocytes respond to UV damage?

Answer 10

They produce pigment.

Question 11

What is MSH?

Answer 11

MSH - Melanocyte Stimulating Hormone

Produced in response to sunlight and UV damage It binds to a G-coupled protein receptor - MC1R This signals to melanocytes via cAMP signalling pathway Variants in MC1R are what regulates pigmentation. Mutation in MSH increases RISK of melanoma, but is not a driving mutation.

Question 12

What is GNAQ?

Answer 12

GNAQ is an accessory protein to a G-coupled protein receptor. Driving mutations in this region are found in ‘Uveal melanoma’ (in the eye). Mutations in GPCR/GNAQ feeds into the RAS pathway, a key pathway where there are mutations that drive melanoma.

Question 13

What mutations can leads to Cutaneous Melanoma?

Answer 13

Mutations in the NRAS pathway or its components. Also components of the PI3K pathway, particularly PTEN and AKT.

Question 14

How is tanning related to DNA damage?

Answer 14

Tanning is a sign that DNA in keratinocytes has been damaged. Pigment production is activated, melanosomes are transferred into the keratinocyte.

Question 15

What inheritance pattern does familial melanoma demonstrate?

Answer 15

Autosomal Dominant Inheritance

Question 16

What is CDKN2A?

Answer 16

CDKN2A is a gene that encodes p16 Many families that suffer from familial melanoma have mutations in this gene. Carriers are heterozygous.

Question 17

What is p16?

Answer 17

p16 is an inhibitor of Rb phosphorylation, acts at a restriction point in the cell cycle. It is encoded by the gene CDKN2A.

Question 18

What is an important genetic locus for familial melanoma?

Answer 18

p16 (CDKN2A) It is an inhibitor of the D-CDK4/6 complex. Acts to hyperphosphorylate Rb in G1 and primes it for transmission through the R point by cyclin E and CDK2.

Question 19

What mutations in CDK4 can interrupt interaction with p16?

Answer 19

Arg24Cys or Arg24His These point mutations disrupt the interaction with p16 and act as a dominant oncogene (only need one mutation). This mutation prevents interaction with the inhibitor.

Question 20

Why is the CDKN2 locus unusual?

Answer 20

It has two alternative exon 1s that encode different gene products. p16ink4A is the inhibitor of CDK46 and it uses the 1α exon. The 1β exon shares the same exon 2 and 3 as 1α but encodes for p14ARF. These use different reading frames. The ATG start codons are located in different locations between the two exons.

Question 21

Within which exon of CDKN2 do most mutations of melanoma occur?

Answer 21

Within exon 2 thus affecting both p16 and p14ARF.

Question 22

What is ARF?

Answer 22

If there is inappropriate proliferation due to viral infection (E1A from adenovirus), inappropriate expression of c-MYC or Ras a large amount of E2F is produced because Rb is phosphorylated. E2F drives the cell through proliferation and initiates DNA synthesis but it also turns on the negative feedback protein, ARF. ARF binds to Mdm2 and releases its inhibition of p53. This triggers either apoptosis or cell cycle arrest.

Question 23

How do mutations in E1A, c-Myc or Ras affect their pathway?

Answer 23

They can lead to a large build up of E2F because Rb is phosphorylated. E2F drives the cell through proliferation and initiates DNA synthesis but also turns on the negative feedback protein ARF. ARF bind to Mdm2 and releases its inhibition of p53 thus triggering either apoptosis or cell cycle arrest.

Question 24

What is Mdm2?

Answer 24

Mdm2 is an important regulator of p53. Mutations in E1A, c-Myc or Ras can lead to production of E2F which activates the negative feedback protein ARF which binds to Mdm2 releasing its inhibition of p53.

Question 25

What can mutations in CDKN2A lead to?

Answer 25

Mutations, typically in exon 2, knock out p16 and regulation of the restriction checkpoint but also it knocks out ARF and compromises the ability of the cell to respond to inappropriate levels of proliferation.

Question 26

What does a mutation in the hTERT gene trigger?

Answer 26

The mutation creates a binding site for Ets family of transcription factors. These are a family that are known to be active in melanocytes and thus this generates a binding site which switches on expression of the hTERT gene in melanocytes, increasing the likelihood of developing tumours.

Question 27

What do mutations in hTERT result in?

Answer 27

Mutations in the hTERT promoter creates binding sites for ETS transcription factors. Dominant mutations- oncogenic. Activates hTERT expression which can lead to increased telomerase activity and immobilisation.

Question 28

How does the Ras pathway function?

Answer 28

In response to the binding of a ligand to a RTK (receptor tyrosine kinase), there is localisation of receptor molecules such as GRB2, SOS and Ras at the cytoplasmic side of the cell membrane. RAS binds to GTP and activates a signalling pathway by phosphorylation. RAF molecules act as dimers, they become phosphorylated and in turn phosphorylate MEK kinase, in melanocytes this acts downstream of ERK. ERK activates a number of genes, either directly via a transcription factor or by phosphorylation that are involved in cell proliferation and survival.

Question 29

What activates the Ras pathway?

Answer 29

Typically the binding of a ligand to a RTK (receptor tyrosine kinase)

Question 30

What percentage of melanomas have an inactivating mutation in BRAF?

Answer 30

About 50%

Question 31

Why are mutations in NRAS or BRAF mutually exclusive?

Answer 31

One mutation is enough to drive the pathway appropriately and switch on proliferation.

Question 32

What mutation is common in BRAF?

Answer 32

90% of BRAF tumours are V600E (Valine to Glutamic Acid)

Question 33

What pathways can mutations in NRAS affect?

Answer 33

The BRAF>MEK pathway The PI3K cell survival pathway.

Question 34

What genes are downstream of ERK?

Answer 34

Cyclin D1 (drives the cell cycle) Negative regulators of MAPK pathway (negative feedback loop) MITF (cell survival factor, melanocyte specific).

Question 35

The activation of which pathway is critical for the development of melanoma?

Answer 35

The Ras/Raf pathway - BRAF mutation in about 50% melanomas - NRAS mutation in 15-20% melanomas - c-KIT in 40% of acral and mucosal melanomas - Loss of NF1 in 4% melanomas - AKT/PTEN mutations often co-occur with BRAF mutations

Question 36

What is NF1?

Answer 36

NF1 is a negative regulator of NRAS activation. GTP phosphatase About 4% of melanomas have a mutation in NF1

Question 37

What are PTEN and AKT?

Answer 37

PTEN and AKT are key regulators of the PI3K pathway. Loss of PTEN, a tumour suppressor OR activating mutations of AKT are often associated with BRAF mutations.

Question 38

What do BRAF mutations mimic?

Answer 38

BRAF mutations mimic the phosphorylation event that activates kinase. Recurrent mutation V600E.

Question 39

Where are BRAF mutations clustered?

Answer 39

BRAF mutations are clustered with the kinase domain.

Question 40

44.50

Answer 40

f