More research is needed on a "promising treatment" for aggressive blood cancer before it can be prescribed on the NHS, a watchdog has said.
The National Institute for Health and Care Excellence (Nice) said nivolumab (Opdivo) - a type of immunotherapy which has shown promise in other cancers - cannot be recommended until more evidence is presented.
It has called on manufacturer Bristol-Myers Squibb (BMS) to provide more UK-based information on the drug's effectiveness for treating people with classical Hodgkin lymphoma.
Clinical trial data on patients with the cancer who have run out of treatment options shows 95% were still alive after a year, with 68% seeing their cancer reduced while on the drug.
Some 8% of patients in the trial 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 lymphoma in the UK each year.
Professor Carole Longson, director of the centre for health technology evaluation at Nice, said: "We recognise that nivolumab is a promising treatment for classical Hodgkin lymphoma, but we need to make sure what the potential benefits are to patients in the UK so that it represents value for money for use in the NHS.
"We are inviting the company to provide more information, including revised analyses, to enable the independent appraisal committee to make a decision based on all the relevant evidence."
Benjamin Hickey, general manager for the UK and Ireland at BMS, said: "Whilst recognising that nivolumab is an innovative and promising medicine, Nice has requested further analyses using UK-specific data for the comparator arm as the original submission relied on US data.
"In order to address questions raised by Nice, BMS are gathering UK-specific data to support the clinical trial data already provided to Nice."
Jonathan Pearce, chief executive of the Lymphoma Association, said: "The news that Nice is minded not to recommend nivolumab, which has shown to be effective in clinical trials, is of concern.
"To not make this treatment available on the NHS will mean limiting treatment options for this group of patients, many of whom are from a younger population, and whose remaining option may only be palliative care.
"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."
'We would urge BMS, Nice and clinicians to work together to reassess the decision and find a solution that would ensure Hodgkin lymphoma patients in England, who are without an alternative, have access to the best possible treatment."
Nivolumab is already licensed for the treatment of advanced melanoma skin cancer and non-small cell lung cancer (NSCLC).