A type of immunotherapy could offer hope to Hodgkin's lymphoma patients who have run out of treatment options.
Nivolumab has received its European licence after promising results in a clinical trial of people with the classic form of the aggressive blood cancer.
The data showed that 95% of patients were still alive after a year, with 68% of patients seeing their cancer reduced while on the drug.
Some patients (8%) had a complete response, which meant doctors could find no evidence of cancer after treatment with nivolumab.
All 80 patients on the trial had cancer that was progressing, despite receiving a stem cell transplant and other treatment.
About 1,700 people are diagnosed with Hodgkin's lymphoma in the UK each year.
Nivolumab is already licensed for the treatment of advanced melanoma skin cancer and non-small-cell-lung-cancer (NSCLC).
The National Institute for Health and Care Excellence (Nice) watchdog has approved nivolumab on the NHS for melanoma patients and is appraising it for lung cancer. The organisation hopes to publish its appraisal on nivolumab for Hodgkin's lymphoma patients next year.
Immunotherapy is a type of treatment that stimulates the body's immune system to fight cancer cells.
Nivolumab targets and blocks a protein called PD-1 on the surface of certain immune cells called T-cells. Blocking PD-1 enables T-cells to find and kill cancer cells.
In October, other clinical trial data showed nivolumab might also help people with untreatable head and neck cancers.
After a year of treatment, 36% of patients on the drug were still alive, compared with 17% of those given standard chemotherapy.
Dr Graham Collins, consultant haematologist at Oxford University Hospitals Foundation Trust, said: "This is a significant step forward for Hodgkin's lymphoma patients.
"Historically, once a patient's cancer progresses to this stage, they are generally placed on palliative end-of-life care.
"The launch of nivolumab changes the treatment landscape, offering an innovative approach to treating this cancer."
Jonathan Pearce, chief executive of the Lymphoma Association, said: "It is vital that innovative treatments are being developed and made available to lymphoma patients.
"We want everyone affected by lymphoma to receive the best possible treatment and care, and the more options there are to improve outcomes and quality of life for patients, the better."
The cost of nivolumab for treating lymphoma is £5,700 a month for the average patient.