The drug rituximab, marketed as MabThera, has been licensed by the Medicines and Healthcare products Regulatory Agency (MHRA) as a treatment for chronic lymphocytic leukaemia (CLL).
In trials it was found that, combined with standard chemotherapy, the drug doubled the number of patients whose symptoms disappeared and halted disease progression for an extra 10.5 months.
As a firstline treatment, rituximab can now be given to newly-diagnosed patients. More than 20,000 in the UK suffer from CLL, and 3,700 new cases are diagnosed each year.
However, rituximab will have to be cleared for NHS use by NICE, the National Institute for Health and Clinical Excellence, which has already approved it for rheumatoid arthritis and non-Hodgkin's lymphoma.
The drug targets cancerous B-cells, a type of white blood cell in the immune system. When antibodies bind to their surface, the cells are forced to self-destruct.
Professor Andrew Pettitt, consultant haematologist at the Royal Liverpool University Hospital and chairman of the UK CLL Forum, said: "The availability of rituximab as an addition to chemotherapy represents a major medical advance for CLL patients here in the UK, giving them the chance of a symptom-free life for a longer period.
"The approval of this treatment is an important step forward in the management of this generally incurable disease."