MMR/Lynch syndrome testing of tumour

Hi there Midgey,

Thanks for reaching out to us here at Macmillan Cancer Support. Welcome to the Online Community – I hope you are finding it a warm and welcoming place to ask questions and seek support. I’m sorry to hear about your recent diagnosis of endometrial cancer. It sounds like your hospital team are very optimistic it’s early and very treatable. I wish you a speedy recovery from your upcoming surgery.

It's natural that you might be worried about a genetic link to this, especially if you are not sure about biological family history. I can see you have some understanding already that Lynch syndrome is a (usually) inherited predisposition to develop certain cancers because of alterations to a set of genes that are responsible for one of the repair systems we have in our cells. DNA (and cells) are continually replicating inside of us as part of healthy body functioning, and there are often ‘typing mistakes’ in this process. Our cells are very sophisticated, and they produce proteins that carry out certain jobs. One of these jobs is to identify these mistakes in DNA transcription and repair the mistakes. We call this the Mismatch Repair system or MMR. If the genes that make the proteins are missing or faulty then the MMR system can be deficient (or not working correctly). If your MMR system doesn’t work correctly there can be more errors in some of the cells that can lead to cancer development over time in certain body tissues. Cancer associated with Lynch syndrome is more common in endometrial (womb) or colorectal (bowel) cancers. It might help to know that of all the endometrial cancers or colorectal cancers we would only expect there to be around 6% (6 in 100) cases associated with Lynch Syndrome.

It is only very recently that the guidelines changed to automatically check for the possibility of Lynch syndrome in these two types of cancer. This is because of advances in our understanding of the human genome, and the discovery that we have two very simple and cost effective tests that can be carried out on tumour samples at point of biopsy that let us know if there is an issue with MMR. The initial results that will indicate if Lynch syndrome is a possibility should come back with the tumour biopsy results, usually within 2 - 3 weeks at the most. If positive for MMR deficiency then this will trigger a different type of testing (germline testing or genetic testing of a blood sample) to confirm this suspicion. This is often preceded by conversations with specialist genetic counselling services or sometimes with the specialist nurse in your hospital team if they have taken on that role and undergone the appropriate training. Although it would be preferable if this happened within 4 weeks, at present this type of test is often taking around 8 – 12 weeks to come back. The priority will be to treat your cancer first though and this wait is unlikely to influence outcomes on that overall.

I can understand why you may be anxious to find out so your children can also be tested. Please be assured this will all unfold in due course and allow plenty of opportunity for careful consideration of the implications and understanding of how genetic testing can be helpful, or sometimes lead to confusing information too. Everyone involved will need a chance to explore what this might mean for them both immediately and in the longer term, and ages and life stages of each individual will be taken into consideration as well as what they want to find out or any risk reducing options they would consider. If identified in family members there will be options to help reduce the risk of cancer occurring. It’s normal for this process to take many months, sometimes longer depending on the family dynamic.

I hope this has helped to reassure you that everything will be taken care of appropriately as things progress.

Please do feel free to give us a call or chat with your Clinical Nurse Specialist as they will be able to talk this over with you in more detail and with knowledge of their local processes.

With best wishes,

Kirstine – Macmillan

Cancer Information Nurse Specialist

You can also speak with the Macmillan Support Line team of experts. Phone free on 0808 808 0000 (7 days a week, 8am-8pm) or send us an email. Ref KDf/ LA

Thank you, Kirstine, for your quick and very detailed response. It's much appreciated.