The Shard is marking Christmas and the New Year by lighting up the top 20 storeys of the London Bridge skyscraper with a series of beams, stripes and sparkles every night.
This year's Shard Lights series began on Monday evening and special displays are planned for Christmas Eve and New Year's Eve.
"Shard Lights is becoming a fixture in London over the Christmas period," said Michael Baker, chief executive of REM, the company that manages the Shard for its owners.
"The installation designed by Woodroffe Bassett creates the capital's highest piece of public art for every Londoner to enjoy.
"The state-of-the-art Guy's Cancer Centre will treat around 6,500 people a year and become a vital hub for the development of new therapies."
Dr Majid Kazmi, clinical director of Guy's Cancer, said: "Guy's and St Thomas' is nearly a thousand years old and has a heritage of providing world-class treatment.
"Moreover, with its location near London Bridge station, Guy's is the best-connected hospital in the UK.
"The recent opening of the state-of-the-art Cancer Centre will enable us to offer pioneering treatments and undertake cutting-edge research to find new solutions for cancer patients across the UK.
"However, to finance the latest technologies and equipment, invest in trials and employ world-leading clinicians, we still need to raise funds. By partnering with The Shard this Christmas, we are raising the funding we need to set a new standard for cancer treatment and honour our heritage as a provider of world-class medical care."