Hello Vicki_76 and thanks for posting, 

Only a small proportion of all breast cancers are due to inherited (germline) gene mutations, most breast cancers are sporadic which means their development is influenced by genetic damage that is picked up over time rather than because of a major inherited mutation. 

In breast cancer, I think germline genetic testing tends to be mostly considered in people who have a strong family history, as this is a predictor of who may be carrying a specific gene mutation. The purpose of testing is often to calculate risk to be able to look into surveillance and preventative measures. In addition genetic testing might be considered for very young women without much of family history and also to look for BRCA 1 and 2 mutations in women under 50 with a type of breast cancer called triple negative. 

It is possible to look for gene mutations in cancer cells but this isn't the same as germline testing. 

Germline mutations in the BRCA1 and BRCA2 genes are far the most common causes of hereditary breast cancer, but overall they are still uncommon and TP53 germline mutations are even rarer.

Germline TP53 mutation are associated with a family predisposition to cancer and in particular Li Fraumeni syndrome. People with Li Fraumeni syndrome have an increased risk of developing a number of cancers including breast and bone cancers, cancer of the adrenal gland, brain tumours, soft tissue sarcomas and a type of leukaemia called acute myeloid leukaemia (AML). This means that carriers usually have a characteristic family history.

A possible but rare late effect of having radiotherapy is that the radiation could contribute to the development of a second new cancer in the area that was treated.  If a person has Li Fraumeni syndromes, this risk is increased so radiotherapy is considered very carefully and used with caution, but there could be situations when it might still be recommended. I think it would be a case by case decision.  

If you have any concerns about your family history or treatment do talk to your own specialist team. 

Please give us a call if you want to talk anything over. Our number is  Freephone 0808 800 4040 and we are here weekdays, 9-5.

Best wishes,

Julia