Grail's flagship cancer detection blood test Galleri is designed to detect more than 50 types of cancer before symptoms appear.

The company, owned by Illumina Inc, said the letters were mistakenly sent by PWNHealth due to a software issue and that it "was in no way related to or caused by an incorrect Galleri test result".

Grail said it had reached out to the patients immediately after the issue, adding that no patient health information has been disclosed or breached due to this.

The software issue being faced by PWNHealth has now been resolved, it said.

Illumina is currently appealing regulatory orders in the U.S. and EU, which are asking the gene sequencing company to divest Grail after it jumped regulators to close its acquisition of the cancer test maker.