A genetically engineered herpes virus, designed to kill cancer cells but leave normal tissue unharmed, has shown early promise in clinical tests, scientists said on Saturday.

The idea of injecting cancer patients with a live virus may seem bizarre, but researchers believe viruses -- which are experts at killing cells -- could one day become a valuable addition to the medical armory against cancer.

The latest progress in a small study using MediGene AG's virus NV1020 was presented at the annual European Society for Medical Oncology conference in Lugano, Switzerland.

NV1020 is a modified version of the herpes simplex virus, which causes cold sores. Its genetic make-up has been altered that so it only replicates in cancer cells, killing them in the process, and leaves ordinary cells alone.

The German biotech company had already announced positive results from an interim analysis of a 13-patient Phase I/II study of NV1020 in September, but efficacy data from a case study was unveiled for the first time at the Swiss meeting.

Axel Mescheder, MediGene's research head, described the case of one very late-stage patient whose cancer had spread to 10 different places around the liver and four in the lungs.

He was given four weekly infusions of the virus followed by two cycles of chemotherapy, and six months after treatment scans showed that his liver tumors had nearly disappeared. The patient survived for 12 months following the intervention.

The reduction in the tumor masses was really impressive in this patient. The hepatic (liver) masses almost disappeared, Mescheder said in a statement.

The results are really quite encouraging at this early stage.

Treating cancer in the liver is notoriously difficult, and the prognosis for patients is very poor. Many people with colorectal cancer, in particular, face the risk that their cancer will metastasize, or spread, to the liver.

The encouraging results with the virus in early human studies follow tests in animals, which showed that NV1020 was effective at killing colorectal and liver cancer cells.

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