Can't remember stuff. Not able to concentrate. Even watching TV is a struggle.
'Chemo brain', also known as 'chemo fog', affects up to half of patients being treated for cancer.
Now a study from the University of Adelaide has opened a door to new strategies for reducing this distressing side effect, referred to by doctors as Cognitive Dysfunction.
The results suggest that the immune system could be to blame, through a gene called MyD88.
"We found that patients were only about half as likely to experience Cognitive Dysfunction if they had an unusual form of MyD88," said Dr Daniel Barratt, a researcher in pharmacology at The University of Adelaide.
Pronounced 'my-dee-eighty-eight', the gene codes for a protein that allows signaling molecules to bind to cells and accelerate immune responses when our bodies detect danger signals. This aspect of immunity is referred to as 'innate'.
The unusual form of MyD88is called a genetic variant, and has a slightly different molecular structure than the most common version.
Variant MyD88 occurs naturally in around a quarter of people to no effect. It's only when cancer strikes that the impact is seen.
"Our results suggest that if you have the variant form of the gene, your innate immune system is less able to become activated through MyD88 and that protects you to some extent from Cognitive Dysfunction associated with cancer," said Dr Barratt.
The study provides the researchers with a new and targeted approach as they look to better understand, treat and prevent Cognitive Dysfunction.
"Cognitive Dysfunction may be due to the cancer itself, to the chemotherapy treatment, to surgery, to radiotherapy or as a result of the use of opioid pain medication," Dr Barratt explained. "Or it could result from a combination of these factors."
"Our results now give us some guidance in terms of where to look to better understand and treat Cognitive Dysfunction in the future: the innate immune system."
Dr Barratt and his colleagues in Australia and Norway plan to conduct more detailed studies, including pre-clinical mechanistic studies of how Cognitive Dysfunction is induced.
They also aim to measure the impact of different opioid pain medications on induction of Cognitive Dysfunction, and to separate different aspects including memory loss and concentration.
"This study gives us a real target to go for," said Dr Barratt.
Dr Barratt is based in the School of Medicine at The University of Adelaide. He conducted this study with Professor Andrew Somogyi, along with colleagues at Norwegian University of Science and Technology, Norway.
The paper was published in the open-access journal PLOS one.