Chemotherapy given to women with advanced ovarian cancer boosts the ability of tumour cells to shield themselves from the immune system, research has shown.
The discovery suggests that patients might benefit more from new immunotherapy drugs if they are administered straight after chemo.
So-called "checkpoint inhibitor" drugs target the ability of cancers to exploit a mechanism designed to prevent "friendly fire" from the immune system.
They could be especially useful to women with advanced ovarian cancer undergoing chemotherapy, scientists believe.
This is because chemotherapy drugs appear to help tumours evade the immune system via the checkpoint mechanism.
Cancers exposed to chemotherapy had higher levels of a protein called PD-L1 that prevented them being recognised and destroyed by immune system T-cells.
Lead author Professor Frances Balkwill, from Barts Cancer Institute at Queen Mary, University of London, said: "Our study suggests that to give patients the best results not only do the immunotherapy drugs need to be given straight after chemotherapy but they also have to able to block PD-L1.
"Clinical trials are now needed to test this theory. This same approach could also be extended to other kinds of cancer where the same types of chemotherapy are used, such as lung cancer."
The findings are published in the journal Clinical Cancer Research.
Each year around 7300 women are diagnosed with ovarian cancer and long-term survival remains just 35 per cent.
Professor Peter Johnson, chief clinician at Cancer Research UK, which funded the study, said: "Treating advanced ovarian cancer is difficult, and in many women unfortunately the cancer returns after initial surgery and chemotherapy treatments. We urgently need new treatments to change this.
"This interesting information about how the immune system may change after chemotherapy may point us to the best way of using new immunotherapy drugs in ovarian cancer."
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