My Malignant Melanoma

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Wednesday, 16 February 2011


Genetic transmission of MM to kids

Someone asked me today on behalf of a mother with MM if she might have transmitted the B-RAF mutation to her kids. Short story- nope.

Longer explanation:

In order for a cancer to spread, a number of the things which prevent uncontrolled growth in normal cells have to go wrong. There are things which repair damage to DNA, limit the number of times a cell can divide, things which cause cells to suicide if they are defective, things which make the immune system kill cells, and so on.

All cancer cells have to have a range of these faults to progress even to a stage 0 cancer. You can be born with faults inherited from your parents that help things along like BRCA, you can pick them up from the action of viruses as in cervical cancer, or from the effect of radiation on DNA as is believed to be the case with the B-RAF mutation, and so on. More commonly, it is thought that a number of these things come together to make cancer.They sequenced MM tumours quite recently, and there were thousands of mutations.

We all have the B-RAF gene, which essentially acts as a check on cell growth. The mutant B-RAF gene's ineffectiveness takes the brakes off cell growth. It exists only in the cancer cells themselves. Blocking this effect is how the B-RAF drugs work. The mutant form is not likely to be in a person with MM's egg or sperm cells, and if it were, there are in any case processes which kill any sex cells with mutations. You don't pass on the mutation.

There is evidence of a familial form of MM, known as dysplastic naevus syndrome, but the suspect gene there is called p16, and the evidence is nowhere near as strong as it is for BRCA- they think other (presently unidentified) genes are involved. Only around 10% of MM has this suspected basis, and those affected have a 50% risk of MM by age 50.

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