More than 400 patients who signed up to take a pioneering oncology detection test developed by US biotech company Grail received erroneous letters last month suggesting they may have developed cancer.

According to an internal company document seen by the Financial Times, 408 patients were incorrectly told they had a signal in their blood suggesting they could have cancer.

Grail said the letters were sent “in error” by its telemedicine provider PWNHealth and that its staff had moved swiftly to contact affected customers to reassure them their test results were wrong.

The incident has generated concern among some insurers who are trialing Galleri, a multi-cancer early detection test that claims to be able to spot more than 50 cancers from a single draw of blood.

MassMutual, one of the biggest US life assurers, said a “small number” of its policyholders had been affected and that it had “paused” its pilot as a result.

“We are aware that Grail proactively reached out to all our participants to address this issue as quickly as possible,” it said.

Principal, another big US life assurer that has customers affected by the error, said it was reviewing its relationship with Grail following the incident.

The episode underlines the risks for insurers in adopting early-detection technologies, which offer the prospect of reducing the amount paid out in claims by keeping customers healthier.

Grail, which is a subsidiary of the world’s biggest gene sequencing company Illumina, is selling Galleri at about $950 per test and marketing it to insurers and large employers. The test scans so-called cell-free DNA for changes caused by cancer cells.

The test has been hailed as “revolutionary” and “cutting edge” by British and US health chiefs, although many experts have urged caution in introducing them before large-scale clinical trials prove they can save lives.

Grail said the erroneous letters were in no way related to or caused by an incorrect Galleri laboratory test result. The letters were inadvertently triggered by a PWNHealth software configuration issue, which had now been disabled, it said in a statement.

PWNHealth said it had promptly launched an investigation and addressed the underlying problem within an hour of becoming aware of it and that it had implemented processes to ensure it did not happen again.

“In partnership with Grail, we started contacting impacted individuals within 36 hours,” it added.

Grail, which is due to make a presentation on Galleri this weekend at the biggest cancer conference in the US, said more than half of individuals who received the letters had not yet had their blood drawn for the Galleri test.

“No patient health information has been disclosed or breached due to this issue, and no patient harm or adverse events have been reported,” the company said.

In February, US life insurance company John Hancock announced it would expand access to Grail’s “first-of-a-kind” test, saying preventive care and early detection was critical to its commitment to help customers live “longer, healthier, better lives.” It collaborated with Munich Re on the pilot announced in September.

A spokesperson for John Hancock said its partnership with Grail had not changed. Munich Re declined to comment.

PWNHealth, which is a subsidiary of Everlywell, a digital health company, is an independent telemedicine vendor which reviews Galleri test requests, prescribes the test and delivers results to patients.

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