# How much can chemotherapy distort one's DNA? **URL:** \ **Category:** Factual Questions\ **Created:** [March 8, 2009, 5:16am UTC](https://boards.straightdope.com/t/how-much-can-chemotherapy-distort-ones-dna/488710 "2009-03-08T05:16:47Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![GrizzRich](https://avatars.discourse-cdn.com/v4/letter/g/7ba0ec/32.png) [@GrizzRich](https://boards.straightdope.com/u/GrizzRich)\ **Post date:** [March 8, 2009, 5:16am UTC](https://boards.straightdope.com/t/how-much-can-chemotherapy-distort-ones-dna/488710/1 "2009-03-08T05:16:47Z")
I have a friend who’s adopted brother (age 16?) has questions regarding his parentage. Basically, he wants to find out if the man he knows as his birth-father is INDEED his birth father. This young man has undergone chemotherapy to treat a non-hodgkins lymphoma and he’s been told (by whom, I don’t know) that the chemo has rendered any DNA testing useless. While I don’t think that’s right, might it be true? ---
**Author:** ![wunderkammer](https://avatars.discourse-cdn.com/v4/letter/w/ed8c4c/32.png) [@wunderkammer](https://boards.straightdope.com/u/wunderkammer)\ **Post date:** [March 8, 2009, 6:01am UTC](https://boards.straightdope.com/t/how-much-can-chemotherapy-distort-ones-dna/488710/2 "2009-03-08T06:01:58Z")
Your friend-of-a-friend-of-a-friend has probably heard the most simplified version of the chemotherapy story–that chemo kills fast dividing cells (including cancerous cells), either by interrupting the machinery of cell division or by messing with their DNA. What your FOAFOAF probably didn’t know is that anticancer drugs don’t work by changing DNA’s nucleotide sequence (that’d be a recipe for more cancer!), but by messing around with DNA’s ability to replicate. Many anticancer drugs work by methylating the DNA, thereby preventing it from uncoiling, by attacking the enzymes (topoisomerases) that untwist the DNA, or by doing other nasty things that completely stop cell division and cause the fast-dividing cells to die off. Paternity testing can’t see any of these epigenetic changes. It’s only concerned with the nucleotide sequence, and that should be pretty much intact in your friend’s remaining healthy cells. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [March 8, 2009, 7:58am UTC](https://boards.straightdope.com/t/how-much-can-chemotherapy-distort-ones-dna/488710/3 "2009-03-08T07:58:26Z")
I think someone may be getting things confused with bone marrow transplants, which are used to treat leukemia. A bone marrow transplant would cause the DNA of the donor to show up in the DNA test. ---
**Author:** ![rekkah](https://avatars.discourse-cdn.com/v4/letter/r/ee59a6/32.png) [@rekkah](https://boards.straightdope.com/u/rekkah)\ **Post date:** [March 8, 2009, 12:18pm UTC](https://boards.straightdope.com/t/how-much-can-chemotherapy-distort-ones-dna/488710/4 "2009-03-08T12:18:27Z")
I think bone marrow transplants are also used sometimes to treat lymphoma. If he had a BMT then the DNA in his blood cells would come from the DNA of the bone marrow donor\*. However, the rest of his tissues would still have his own DNA, so something like a bucchal swab (wiping a swab round the inside of the cheek to collect loose skin cells) would still provide DNA that could be used in a paternity test. \*Unless it was an autologous BMT where the patients own cells are used for the transplant. ---
**Author:** ![Goblinboy](https://avatars.discourse-cdn.com/v4/letter/g/3be4f8/32.png) [@Goblinboy](https://boards.straightdope.com/u/Goblinboy)\ **Post date:** [March 8, 2009, 5:03pm UTC](https://boards.straightdope.com/t/how-much-can-chemotherapy-distort-ones-dna/488710/5 "2009-03-08T17:03:50Z")
Chemotherapy drugs are purged from your system within days, if not hours, of taking them as well. The aftereffects linger for weeks, of course. Maybe he was told that he couldn’t donate blood and he got the impression that it was damaged? My doctor told me it wasn’t even an option once I’d had cancer. ---
**Author:** ![The\_Second\_Stone](https://avatars.discourse-cdn.com/v4/letter/t/bbe5ce/32.png) [@The\_Second\_Stone](https://boards.straightdope.com/u/The_Second_Stone)\ **Post date:** [March 8, 2009, 6:20pm UTC](https://boards.straightdope.com/t/how-much-can-chemotherapy-distort-ones-dna/488710/6 "2009-03-08T18:20:08Z")
I think that your friend of the brother may be talking to someone who suspects or knows that the “birth” father is not the real father.